sports medicine Volume 40 Issue 2 February 2010

Sports Med 2010; 40 (2): 95-111 0112-1642/10/0002-0095/$49.95/0 CURRENT OPINION ª 2010 Adis Data Information BV. All r...

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Sports Med 2010; 40 (2): 95-111 0112-1642/10/0002-0095/$49.95/0

CURRENT OPINION

ª 2010 Adis Data Information BV. All rights reserved.

Recommendations for Improved Data Processing from Expired Gas Analysis Indirect Calorimetry Robert A. Robergs,1,2 Dan Dwyer3 and Todd Astorino4 1 2 3 4

Exercise and Sports Sciences, University of Western Sydney, Sydney, New South Wales, Australia Exercise Physiology Laboratories, University of New Mexico, Albuquerque, New Mexico, USA Exercise Science, University of Newcastle, Newcastle, New South Wales, Australia Department of Kinesiology, California State University, San Marcos, California, USA

Abstract

There is currently no universally recommended and accepted method of data processing within the science of indirect calorimetry for either mixing chamber or breath-by-breath systems of expired gas analysis. Exercise physiologists were .first surveyed to determine methods used to process oxygen consumption (VO2) data, and current attitudes to data processing within the science of indirect calorimetry. Breath-by-breath datasets obtained from indirect calorimetry during incremental exercise were then used to demonstrate the consequences of commonly used time, breath and digital filter post-acquisition data processing strategies. Assessment of the variability in breath-by-breath data was determined using multiple regression based on the independent variables ventilation (VE), and the expired gas fractions for Based on the oxygen and carbon dioxide, FEO2 and FECO2, respectively. . results of explanation of variance of the breath-by-breath VO2 data, methods of processing to remove variability were proposed for time-averaged, breathaveraged and digital filter applications. Among exercise. physiologists, the strategy used to remove the variability in sequential VO2 measurements varied widely, and consisted of time averages (30 sec [38%], 60 sec [18%], 20 sec [11%], 15 sec [8%]), a moving average of five to 11 breaths (10%), and the middle five of seven breaths (7%). Most. respondents indicated that . they used multiple criteria to establish maximum VO2 (VO2max) including: the attainment of age-predicted maximum heart rate (HRmax) [53%], respiratory exchange ratio (RER) >1.10 (49%) or RER >1.15 (27%) and a rating of perceived exertion (RPE) of >17, 18 or 19 (20%). The reasons stated for these strategies included their own beliefs (32%), what they were taught (26%), what they read in research articles (22%), tradition (13%) and the influence of their colleagues (7%). The combination of VE, FEO2 and FECO2 removed . breath-by-breath variability in incremental and steady-state 96–98% of VO 2 . . exercise VO2 data sets, respectively. Correction of residual error in VO2 datasets to 10% of the raw variability results from application of a 30-second time average, 15-breath running average, or a 0.04 Hz low cut-off digital filter. Thus, we recommend that once these data processing strategies are

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used, the peak or maximal value becomes the highest processed datapoint. Exercise physiologists need to agree on, and continually refine through empirical research, a consistent process for analysing data from indirect calorimetry.

Exercise testing that incorporates the use of indirect calorimetry to calculate whole body rates . of oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory exchange ratio (RER) and energy expenditure has a long history dating back to the late 19th century.[1] Hill[1] and Hill and Lupton[2] further consolidated the scientific base of the application of indirect calorimetry to study body metabolism and physiology during exercise in the 1920s. Hill introduced the scientific community to the presence of a plateau . in VO2 during discontinuous incremental exercise testing, . the measure of the maximal rate of . VO2 (VO2max), and provided at that time an interpretation, based on logic and not empirical evidence, of the central cardiovascular and . pulmonary determinants of VO2max. Numerous reviews and both supportive[3-7] and critical commentaries[8-11] have been written on the historic work of Hill and his contributions to the academic field and developing professions of exercise physiology and the exercise and sports sciences. Within the first 60 years after Hill’s pioneering work, researchers identified the need to establish . criteria to classify VO2 responses to incremental exercise as being truly maximal.[12-17] The most notable and influential of these studies was published in 1955 by Taylor et al.[17] In this study, men (n = 115) were required to complete multiday discontinuous treadmill testing characterized by both walking and running. To confirm attain. ment. of VO2max, these scientists used a change in VO2 500 datapoints/test for a typical VO2max protocol. However, today many researchers are now sufficiently trained in electronics and computer programming to write their own software based on a variety of software platforms, develop their own systems, and use a myriad of software applications to easily process large data files generated from indirect calorimetry. Today, more than ever before, scientists need direction for how to process data from indirect calorimetry. Unfortunately, research and explanation of how to process this increasing volume of data has not kept up with the technological progress experienced in the field of indirect calorimetry and the training of many of today’s physiological scientists. Sports Med 2010; 40 (2)

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. 4. Breath-by-Breath VO2 Data: Deciphering Signal from Noise

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To acquire data from every breath involves the collection of approximately 12 datapoints/min at rest, to more than 60 datapoints/min during exercise at volitional fatigue. Any user of a breathby-breath system of indirect calorimetry will attest to the high degree of variability in the data, and recognize the obvious dilemma that follows: what is the most valid way to decrease this variability, and to what extent should this variability be decreased? An important first step prior to answering these questions is to present and explain the contributing factors causing variability in the typical breath-by-breath response to incremental exercise testing. A clear understanding of the

origin and magnitude of this variability is essential for recognizing the need to reduce the variability via one of several processing options. Figure 1 presents steady-state breath-by. breath data for VO2, ventilation, tidal volume, breathing frequency, heart rate (HR), oxygen pulse and expired gas fractions for oxygen (FEO2) and carbon dioxide (FECO2). Data from figure 1 reveal that there is considerable variability in all signals. Close visual inspection also reveals a similar pattern of variability between . variables. With reVO2 and ventilation-derived . spect to the VO2 data, the constant metabolic demand of this exercise condition resulted in . breath-by-breath VO2 data that averaged (mean – SD) 2.17 – 0.3 L/min, with a range of 1.4–3.3 L/min. To assume that breath-by-breath . VO2 data reflect body metabolism resolved to

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Fig. 1. Stack plots of pertinent variables measured . and computed from expired gas exchange indirect calorimetry during steadystate exercise (calculated from oxygen consumption [VO2] and heart rate). FEO2 = oxygen pulse, and expired gas fractions for oxygen; FECO2 = oxygen pulse, and expired gas fractions for carbon dioxide; STPD = Standard Temperature and Pressure, Dry; VE = ventilation.


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each breath is to assume that body metabolism deviates by as much as 86% during steady-state exercise. Although data at this frequency of col. lection for muscle VO2 has never been collected due to methodological constraints, we feel that it is logical to conclude that such a magnitude of muscle metabolic variability does not occur. For example, application of the Fick equation reveals that if such variability was real, then either muscle blood flow or oxygen extraction, or a combination of the two, would need to collectively change by this magnitude and cause similar oscillatory perturbations in alveolar ventilation and external respiration. We know of no evidence to support this interpretation. This assumed non-metabolic origin of the varia. bility in breath-by-breath VO2 means that a large . portion of the VO2 variability is caused by other variables/conditions. What variables account for this variability, and how much of the variability can be accounted for, are questions that have been addressed and adequately answered by past research. [29] measured breath-by-breath . Potter et al. VO2 in children and showed that tidal volume accounted . for a large proportion of variability for each of VO2 (43%) and VCO2 (49%), with additional variance explanation provided by breath. ing frequencies (22%) for both VO2. and VCO2. Myers et al.[30,31] reported 51% of VO2 variance due to tidal volume, with smaller contributions from breathing frequencies (25%). Data from LaMarra et al.[22] corroborated these findings,. as these scientists stated that breath-by-breath VO2 variability was due to natural breathing imperfections (irregularities). Clearly, past research shows that the variability in ventilation on a breathby-breath basis causes the majority of variability, close to 70%, in any gas volume computation in indirect calorimetry. As this past research has by no means been thorough, or included all possible ª 2010 Adis Data Information BV. All rights reserved.

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Pred VO2 = (0.0495(VE)) − (26.2398(FEO2)) + 4.2202 R2 = 0.984 SEE = 0.07 L/min

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variables that may alter metabolic computations (such as expired gas fractions), it is also likely that ventilatory parameters may account for an even larger proportion of explained variance. We completed a multiple regression analysis of . the data from figure 1, where VO2 was the dependent variable, and ventilation, breathing frequency, FECO2 and FEO2 were independent variables. We assumed that steady-state data reflect random signal generation, where each datapoint has independence from one .another in reflection of the actual whole body VO2. Based on a step-wise data entry model, multiple regression analysis produced the results presented in table I. Figure 2a presents the raw and predicted . VO2 data from figure 1, and. the resulting line of best fit. Breath-by-breath VO2 variability was

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Table I. Results from the multiple regression analysis of breath-bybreath oxygen consumption variability

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. Fig. 2. (a) Prediction of oxygen consumption (VO2) based on the independent variables ventilation (VE) and expired gas fractions for oxygen (FEO 2). The two independent variables accounted for 98% of the . raw VO2 variability. (b) Residuals analysis shows the near-even error distribution across the range of measurement, with a mean – SD residuals error = 0.000 – 0.069 L/min. SEE = standard error of estimate.

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98% explained by a two-factor model comprising ventilation and FEO2. Figure 2b presents the residual distribution from the prediction. Such variability is magnified in the . breath-by-breath computation of ventilation, VO2 and VCO2 due to the convention of expressing this data relative to minute time intervals, thereby multiplying the breath-by-breath volume error by a factor (60/breath interval time [s]) that can range from 12 (rest) to 75 (peak exercise). . We applied the same statistical logic to a VO2 dataset from the linear segment obtained during a ramp incremental exercise protocol (figure 3a). Linear regression was applied to this data segment to derive the line of best fit and the computation of residuals (figure 3b). Multiple regression gave similar results to the steady-state

4.1 Options for Attenuating Variability . in Breath-By-Breath VO2 Data

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There are three general approaches that one can use to . attenuate the variability in breathby-breath VO2: time averages, breath averages and digital filtering.

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data, where a three-variable model of ventilation, accounted for FECO2 and FEO2 (p < 0.0001) . 99.46% of the variability in VO2, with a standard error of estimate (SEE) of 0.09 L/min. Given the clear evidence from our data, as well all of as from other researchers,[22,29-31] almost . the breath-by-breath variability for VO2 during both steady state and incremental exercise is caused by irregularities in the rate and depth of ventilation, which by definition and physiology also influences HR, FEO2 and FECO2, especially during low to moderate exercise intensities. The obvious question is how to remove this variability to better reflect what we . assume to be the smoother muscle VO2 response to metabolic demand?

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. Fig. 3. (a) Data for oxygen consumption (VO2) from the linear segment of an incremental exercise test, with the line of best fit based on multiple regression prediction from ventilation and expired gas fractions for carbon dioxide and oxygen. (b) The remaining residuals from the multiple regression prediction (mean – SD residuals = -0.0005 – 0.1991).


Based on our preliminary survey, time averages remain . the most common approach to processing VO2 data. Such averaging is typically a fixed time period such as 15, 30 or 60 seconds. All breaths within the time window are used for the calculation. Breath averages are computed for a fixed number of breaths and these data are plotted versus time. Figures 4 and 5 present data for one individual during cycle ergometry exercise to volitional fatigue. The data were processed by time averages (figure 4a–e) and breath averages (figure 5a–e), with time-averaged data aligned to the end of the time interval based on what we view to be the current conventional, not necessarily correct (alignment should occur to the centre of the time interval), presentation. As revealed by the data in figures 4 and 5, time and breath averaging approaches are crude smoothing tools and have weaknesses in how they represent the measures of interest. For example, because the time interval between Sports Med 2010; 40 (2)


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the protocol increased from 2 to 10 and 12 to 38, respectively. Conversely, when using breath averages, the time period in an averaging window shrinks during transitions from rest to maximal exercise. The data in figure 5 reveal that for the 5- and 21-breath averages, the range of time included in each average decreased from 0.51 to 0.1

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. adjacent breaths decreases as VO2 increases, the number of breaths/unit time increases with increases in exercise intensity. For the 15-second to 1-minute average comparison, the number of breaths/time interval from the start to the end of ª 2010 Adis Data Information BV. All rights reserved.

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and from 1.62 to 0.44 minutes, respectively. In addition, both approaches involve no attempt to determine what specific component of variability is attenuated and what information should remain. The net result from time and breath averaging is an uneven degree of processing across the data set. In addition, how well do time and breath averages remove the ventilationinduced variability, and leave what may actually . reflect muscle- or cardiopulmonary-derived VO2 characteristics? When does breath and time averaging become too crude and actually remove important data and trends that have physiological meaning to oxygen supply and demand, .and perhaps even.to the ability to validly detect a VO2 plateau and VO2max? 4.1.2 Digital Filtering

Use of techniques such as digital filtering are common in engineering and biomechanics, but are not . typically used in processing breath-bybreath VO2 data. This is unfortunate, as the data in figures 1–3 revealed that there. are multiple explanations for the variability of VO2 data when acquired breath-by-breath, with the majority of this variability accounted for by ventilation and related parameters. These multiple contributors . to the final VO2 data signals have the potential to be independently removed if they occur at different rates, or frequencies, . to the variability introduced to whole body VO2 by muscle metabolism or cardiopulmonary physiology. To illustrate the multiple components that re. side within breath-by-breath VO2 at an absolute steady-state exercise intensity, we present data in figure 6a–e based on the assumptions and simulation of a relatively rapid low magnitude oscil. lation in muscle VO2, a slow medium magnitude cardiovascular oscillation that will influence gas delivery and removal from muscle, and a very slow high magnitude ventilatory oscillation profile. Each component (muscle, cardiovascular and ventilatory) has a unique frequency with a different time offset, which when combined and sampled randomly reveal the overall variability . that we might see when quantifying in VO 2 . VO2 from expired gas analysis indirect calorimetry. Figure 6d is not that dissimilar from the ª 2010 Adis Data Information BV. All rights reserved.

real data presented in figure 1a. Furthermore, and as expected based on the simulated data, the digital filtering removed all of the high magnitude ventilatory variability, most of the cardiovascular variability, and left a dataset pre. dominantly influenced in theory by muscle VO2 kinetics (figure 6e). The most . valid method to process breathby-breath VO2 data would be to specifically remove as much extraneous variability as possible, while minimally altering the variability inherent within the remaining data signal. The problem here though is that in reality we do not know . what the muscle VO2 kinetics are across the signal sampling range of 0.2–1.5 Hz (typical range for breathing frequency across an incremental protocol to volitional fatigue). Furthermore, this muscle response may be irrelevant given the mixing of metabolic gases in the central mixed venous blood volume, which would provide a physiological smoothing function driven by ventilation. As such, when using expired gas analysis indirect calorimetry, the cause of the remaining variability is likely to be cardiopulmonary rather than muscular. 4.1.3 Data Distortion

Although it would be convenient to assume . that a digital filter is the perfect answer to VO2 data processing, the fact is that no method of data processing is perfect. For the digital filter, the lower cut-off frequency selected for the processing can have a profound influence on the resulting data trend. A cut-off filter too high does not remove enough variability. A cut-off filter too low can alter, or distort, the data trend. Data distortion also results from time averages, as shown in figure 7a, with no distortion for breath averages if this is done incrementally and not as a block average (figure 7b). To show the results . of data distortion from digital filtering of VO2 data from incremental exercise, figure 7c presents the raw and resulting digitally filtered data for different low cut-off frequencies. Such low cut-off frequencies can be interpreted as allowing only variability to remain in the data at a frequency lower than the cutoff value. As such, all variability resonating at Sports Med 2010; 40 (2)


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frequencies higher than the cut-off are excluded and the datapoints of these higher frequency variability responses are changed to fit a lower frequency smaller magnitude profile tolerated by the low frequency cut-off value. The data in figure 7c reveal that low cut-off frequencies above 0.08 . Hz do not provide adequate reduction in VO2 data variability, but clearly fit the raw data well. On the other extreme, cut-off frequencies lower than 0.03 Hz provide dramatic reductions in data variability, yet induce a clear distortion of ª 2010 Adis Data Information BV. All rights reserved.

the data seen as a downward-right adjustment of the data and trend. The obvious question is when does the digital filtering begin to alter the true trend of the raw data? We decided to base our procedures on the methods used within the field of biomechanics. For example, Winter[32] has recommended that the optimal cut-off frequency can be determined from the line of best fit resulting from a linear regression applied to a subset of the range of residuals versus a range of low cut-off frequencies. Sports Med 2010; 40 (2)

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Fig. 7. Data distortion resulting from processing with (a) a 60-second time average, (b) a 21-breath running average and (c) multiple examples of a .low frequency cut-off digital filter (Butterworth third order). The data used .in these figures are from a linear portion of oxygen consumption (VO2) data from a cycle ergometry ramp incremental protocol to maximum VO2.

The residuals are computed from the expected data value (from line of best fit) and that obtained after applying the low frequency cut-off digital filter. Presumably, the residuals error from digital filtering at higher cut-off frequencies induces a small negative change in the mean residual, with this error increasing as the lower cut-off frequency is decreased. Winter[32] has explained that this increasing error fits a linear function until ª 2010 Adis Data Information BV. All rights reserved.

the lower cut-off frequency is decreased to a certain frequency, after which dramatic increases in error result. It was proposed that the y-intercept of this linear regression can be used to extend out horizontally, and where it intersects the residuals plot reveals the recommended lower cutoff frequency. . We present this graphic for the . linear VO2 segment of data from a test to VO2max for a Sports Med 2010; 40 (2)


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representative subject during cycle ergometry in figure 8. The data in figure 8 clearly show that the residuals error response over a range of cut-off frequencies is nonlinear, and is accurately modelled by a two-segment exponential decay function. As no initial linear relationship exists, the recommendations of Winter[32] for objectively detecting the lower . cut-off frequency does not have validity for VO2 data. An alternate approach is to predetermine what is an acceptable level of signal variability reduction based on residuals analysis from a line of best fit. Previously, we demonstrated that measures of ventilation, FECO2 and FEO2 account for approximately 96–98% of variability in breath. by-breath VO2. Conversely, prior research has shown variance explanation closer to 90%.[22,29-31] Given the lack of research on this topic, and especially research using multiple prediction variables

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Fig. . 9. Data for (a) measured and predicted oxygen consumption (VO2) based on the independent variables ventilation and oxygen pulse, and expired gas fractions for oxygen. The residuals error was then decreased by (b) 80% and (c) 95% to reveal smoothed graphical presentations of the data set.

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Fig. 8. The increase in mean residuals resulting from a comparison of digital filtering at cut-off frequencies ranging from 0.001 to 0.25 Hz. The data for this presentation are . from a subject with a linear increase in oxygen consumption (VO2) during incremental exercise to . maximum VO2. The residuals represent the difference between the digital . processed datapoints and the linear regression prediction of the VO2. The inner plot shows the curvilinear nature of the relationship throughout even for the higher values of the cut-off frequency range.


that also adjust for expired gas fractions (as we do in this report), at this time it seems prudent to develop a processing strategy that removes approximately 90% . of the original breath-by-breath variability in VO2. To illustrate this recommendation, figure 9a presents the raw . (dataset used for figure 1a) and predicted VO2 data from the regression prediction with the independent Sports Med 2010; 40 (2)

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. Fig. 10. Data for (a) measured and predicted oxygen consumption (VO2) based on 90% residuals error as described in the text. The same raw . VO2 data are presented as (b) 30-second averages, (c) 15-breath averages, and (d) after a 0.04 Hz digital filter.

variables of ventilation and FEO2. We then adjusted for 80% and 95% of the residual error (20% and . 5% of each residual, respectively) for each VO2 datapoint and plotted each result in figure 9b and c. To assess how such residuals error reduction . alters VO2 data from incremental exercise, we then applied a 90%.residual error reduction to the linear . segment of VO2 data acquired from a test to VO2max (figure 10 for data from figure 3). The data processing required to approximate 90% error reduction (SScorr = SS raw · 0.1, where SScorr = sum of squares corrected, and SS = sum of squares) [figure 10a] results from a time average of 30 seconds (figure 10b), a 15-breath running average (figure 10c), and a low cut-off frequency digital filter of 0.04 Hz (figure 10d). ª 2010 Adis Data Information BV. All rights reserved.

5. Recommendations for Processing Data from Indirect Calorimetry Based on the prior content, we are now ready to recommend strategies for processing data acquired from indirect calorimetry. If a time-averaged system has to be used, we recommend no longer than a 30-second time average (figure 4b) where the data are aligned to the central time of the interval period, which is 15 seconds, and thereby require time representation of 0, 0.25, 0.75, 1.25, 1.75, 2.25 minutes, etc. We also recommend that exercise physiologists who currently use expired mixing chamber systems, with no choice of other sampling and processing options, strive to equip themselves with software that will support acquisition and data processing Sports Med 2010; 40 (2)


as breath averages. While a 30-second average provides reasonable reductions in data variability, it provides unreasonable decreases in data frequency, which will detract from how the data can be used to assess important physiology measurements and trends. For breath-by-breath systems and averaging systems suited to breath averages, we recommend a 15-breath running average, aligned to the time of the central breath, which is the eighth breath (figure 10c). Although we identified several theoretical problems with a breath average, the alternative of a digital filter requires a degree of mathematical computation and software dependence that simply does not exist in software of all commercial systems of indirect calorimetry. Furthermore, given that the 15-breath average induces minimal data loss (lose initial seven and last seven datapoints), has no data and trend distortion, can be accomplished with the software of many commercial indirect calorimetry systems, and, if not, can be easily applied to datasets with post-acquisition spreadsheet computation, it is a reasonable expectation that all scientists and practitioners can do this data processing. For scientists able to implement digital filters in their data processing, we recommend a low cut-off frequency digital filter of 0.04 Hz. 5.1 Recommendations for Detecting the Highest Value Datapoint

Once the recommended data processing strategies are used, then the task of detecting the peak or maximal value of any variable is simple. The highest, peak or maximal value becomes the highest processed . Thus, for time. datapoint. or VO averaged systems, VO2max 2 peak would be . for. the test. the highest 30-second VO2 average . or VO2 peak For breath-by-breath data, VO2max . would be the highest 15-breath VO2 average for the test. For exercise physiologists who can apply a 0.04 Hz low frequency cut-off digital. filter, the . largest single datapoint is VO2max or VO2 peak. Exercise physiologists need to agree on a consistent process for analysing data from indirect calorimetry. We feel that our recommendations are valid, based on empiricism, and if adopted ª 2010 Adis Data Information BV. All rights reserved.

109

can improve the quality of research and data interpretation in exercise physiology, sport and exercise science, and both basic and applied physiology. We encourage researchers to further assess our recommendations and rationale, to scientifically test our methods and recommendations, and thereby contribute to the refinement of these recommendations. As with any science, we acknowledge the need to continually improve on methods of data acquisition and interpretation, and we see this commentary as a major step forward in this . continually evolving process. Once VO2 data is more consistently processed and presented in peer-review research, perhaps we will then be in a better position to more validly comment . on such topics. as the validity of or need for the VO2 plateau at VO2max.[33,34,36,37] Acknowledgements No sources of funding were used to assist in the preparation of this review. The authors have no conflicts of interest that are directly relevant to the content of this review.

Appendix A Original Data Acquisition from Indirect Calorimetry

All original data presented in this manuscript were collected using a custom-developed indirect calorimetry system. Subjects ventilated air through a standard one-way mouthpiece configuration (Hans Rudolph, Shawnee, KS, USA). Expired air passed through a unidirectional flow turbine (KL Engineering, Van Nuys, CA, USA) connected to the expired port of the mouthpiece, and then inseries to a compliant 3 L mixing bag (Erich Jaeger, Friedberg, Germany). Mixed expired air was sampled from the mixing bag and analysed for oxygen and carbon dioxide content using electronic analysers (AEI Technologies, Pittsburg, PA, USA) with a time delay of 2.5 seconds. Analogue signals from the turbine and analysers were acquired in real time using commercial hardware (National Instruments, Austin, TX, USA), and processed in real time using custom-developed software (LabVIEW, National Instruments, Austin, TX, USA). Sports Med 2010; 40 (2)

Robergs et al.

110

Steady-State Simulated Data

. It was assumed that breath-by-breath VO2 data is influenced by three inherent sine-wave rhythms: muscle metabolism, cardiovascular function and ventilation. The respective signal features of these rhythms were as follows. Muscle: sine-wave frequency = 0.5 Hz, phase = 0, amplitude = 0.1 L/min, mean = 2.17 L/min, sampling frequency = 5 Hz, total samples = 250. Cardiovascular: sine-wave frequency = 0.225 Hz, phase = 45, amplitude = 0.25 L/min, mean = 2.17 L/min, sampling frequency = 5 Hz, total samples = 250. Ventilation: sine-wave frequency = 0.1 Hz, phase = 90, amplitude = 0.8 L/min, mean = 2.17 L/min, sampling frequency .= 5 Hz, total samples = 250. The final simulated VO2 response was derived by interleaving the three data arrays (muscle, cardiovascular, ventilation) and then completing 250 random samples from this larger array by computer-generated random sampling (LabVIEW, National Instruments, Austin, TX, USA).

References 1. Lusk G. The elements of the science of nutrition. Philadelphia (PA): WB Saunders, 1928 2. Hill AV. Muscular activity. London: Tindall and Cox, 1925 3. Hill AV, Lupton H. Muscular exercise, lactic acid, and the supply and utilization of oxygen. Q Q J Med 1923; 16: 135-71 4. Bassett DR, Howley ET. Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exerc 2000; 32: 70-84 5. Bassett DR, Howley ET. Maximal oxygen uptake: ‘‘classical’’ versus ‘‘contemporary’’ viewpoints. Med Sci Sports Exerc 1997; 2: 591-603 6. Bergh U, Ekblom B, Astrand P. Maximal oxygen uptake ‘‘classical’’ versus ‘‘contemporary’’ viewpoints. Med Sci Sports Exerc 2000; 32: 85-8 7. Howley ET, Bassett DR, Welch HG. Criteria for maximal oxygen uptake: review and commentary. Med Sci Sports Exerc 1995; 27: 1292-301 8. Noakes TD. Implications of exercise testing for prediction of athletic performance: a contemporary perspective. Med Sci Sports Exerc 1988; 20: 319-30 9. Noakes TD. Challenging beliefs: ex Africa semper aliquid novi. Med Sci Sports Exerc 1997; 9: 571-90 10. Noakes TD. Maximal oxygen uptake: ‘‘classical’’ versus ‘‘contemporary’’ viewpoints: a rebuttal. Med Sci Sports Exerc 1998; 30: 1381-98 11. Robergs RA. An exercise physiologist’s ‘‘contemporary’’ interpretations of the ‘‘ugly and creaking edifices’’ of the . VO2max concept. JEPonline 2001; 4 (1): 1-44


12. Cumming GR, Borysyk LM. Criteria for maximum oxygen uptake in men over 40 in a population survey. Med Sci Sports Exerc 1972; 4: 18-20 13. Froelicher Jr VF, Brammell H, Davis G, et al. A comparison of three maximal treadmill exercise protocols. J Appl Physiol 1974; 36: 720-5 14. McArdle WD, Katch FI, Pechar GS. Comparison of continuous . and discontinuous treadmill and bicycle tests for maxVO2. Med Sci Sports Exerc 1973; 5: 156-60 15. Mitchell JH, Blomqvist G. Maximal oxygen uptake. New Engl J Med 1971; 284: 1018-22 16. Mitchell JH, Sproule BJ, Chapman CB. The physiological meaning of the maximal oxygen intake test. J Clin Invest 1958; 37: 538-46 17. Taylor HL, Buskirk E, Henschel A. Maximal oxygen intake as an objective measure of cardio-respiratory performance. J Appl Physiol 1955; 8: 73-80 18. American College of Sports Medicine. ACSM’s guidelines for exercise testing and prescription. Philadelphia (PA): Lippincott Williams and Wilkins, 2005 19. Wyndham CH, Strydom NB, Maritz JS, et al. Maximal oxygen intake and maximum HR during strenuous work. J Appl Physiol 1959; 14: 927-36 20. Beaver WL, Wasserman K, Whipp BJ. On-line computer analysis and breath-by-breath graphical display of exercise function tests. J Appl Physiol 1973; 34: 128-32 21. Beaver WL, LaMarra N, Wasserman K. Breath-by-breath measurement of true alveolar gas exchange. J Appl Physiol 1981; 51 (6): 1662-75 22. Lamarra N, Whipp BJ, Ward SA, et al. Effect of inter-breath fluctuations on characterizing exercise gas exchange kinetics. J Appl Physiol 1987; 62 (5): 2003-12 23. Roecker K, Prettin S, Sorichter S. Gas exchange measurements with high temporal resolution: the breath-by-breath approach. Int J Sports Med 2005; 26: S11-8 24. Whyte GP, Sharma S, George K, et al. Exercise gas exchange responses in the differentiation of pathologic and physiologic left ventricular hypertrophy. Med Sci Sports Exerc 1999; 31 (9): 1237-41 25. Day JR, Rossiter HB, Coats EM, et al. The maximally . attainable VO2 during exercise in humans: the peak vs. maximum issue. J Appl Physiol 2003; 95 (5): 1901-7 26. Duncan GE, Howley ET, Johnson BN. Applicability of . VO2max criteria: discontinuous versus continuous protocols. Med Sci Sports Exerc 1997; 29: 273-8 27. Dwyer DB. A standard method for determination of maximal . aerobic power from breath-by-breah VO2 data obtained during a continuous ramp test on a bicycle ergometer. JEPonline 2004; 7 (5): 1-9 28. Pearce DH, Milhorn HT, Holoman GH, et al. Computerbased system for analysis of respiratory responses to exercise. J Appl Physiol 1977; 42: 968-75 29. Potter CR, Childs DJ, Houghton W, et al. Breath-to-breath ‘‘noise’’ in the ventilatory and gas exchange responses of children to exercise. Eur J Appl Physiol Occup Physiol 1999; 80 (2): 118-24 30. Myers J, Walsh D, Buchanan N, et al. Can maximal cardiopulmonary capacity be recognized by a plateau in oxygen uptake? Med Sci Sports Exerc 1989; 96: 1312-6

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31. Myers J, Walsh D, Sullivan M, et al. Effect of sampling on variability and plateau in oxygen uptake. J Appl Physiol 1990; 68: 404-10 32. Winter DA. Biomechanics and motor control of human movement. 3rd ed. Hoboken (NJ): Wiley Publishers, 2005 33. Astorino TA, Robergs RA, . Ghiasvand F, et al. Incidence of the oxygen plateau at VO2max during exercise testing to volitional fatigue. JEPonline 2000; 3 (4): 1-12 34. Doherty M, Nobbs L, Noakes TD. Low frequency of the ‘‘plateau phenomenon’’ during maximal exercise in elite British athletes. Eur J Appl Physiol 2003; 89: 619-23 35. Freedson P, Kline G, Porcari J, et al. Criteria for defining . VO2max: a new approach to an old problem [abstract]. Med Sci Sports Exerc 1986; 18: S36


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. 36. Weir JP, Koerner S, Mack B, et al. VO2 plateau detection in cycle ergometry. JEPonline 2004; 7 (2): 55-62 . 37. Howley ET. VO2max and the plateau: needed or not? Med Sci Sports Exerc 2007; 39 (1): 101-2 38. Macfarlane DJ. Automated metabolic gas analysis systems: a review. Sports Med 2001; 31 (12): 841-61

Correspondence: Robert A. Robergs, Head of Program: Sport and Exercise Science, School of Biomedical and Health Sciences, Building 20, The University of Western Sydney – Campbelltown Campus, Locked Bag 1797, Penrith South DC, NSW 1797, Australia. E-mail: [email protected]

Sports Med 2010; 40 (2)

Sports Med 2010; 40 (2): 113-139 0112-1642/10/0002-0113/$49.95/0

REVIEW ARTICLE


Guidelines for Glycerol Use in Hyperhydration and Rehydration Associated with Exercise Simon Piet van Rosendal,1 Mark Andrew Osborne,2 Robert Gordon Fassett1,3 and Jeff Scott Coombes1 1 School of Human Movement Studies, The University of Queensland, Brisbane, Queensland, Australia 2 Queensland Academy of Sport, Brisbane, Queensland, Australia 3 Royal Brisbane and Women’s Hospital, Brisbane, Queensland, Australia

Contents Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Considerations for Glycerol Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Glycerol Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Volume of Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Type of Fluid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Timing of Fluid with Glycerol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Duration of Hyperhydration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 Guidelines for Pre-Exercise Glycerol Hyperhydration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Glycerol Ingestion during Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Glycerol Ingestion during Exercise, after Pre-Exercise Hyperhydration . . . . . . . . . . . . . . . . . . . . . . 2.2 Glycerol Ingestion during Exercise, without Pre-Exercise Hyperhydration. . . . . . . . . . . . . . . . . . . . 2.3 Guidelines for Glycerol Ingestion during Exercise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Glycerol as a Rehydrating Agent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Areas for Further Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Side Effects from Glycerol Consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Summary and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Abstract

113 115 115 115 127 130 131 131 132 132 133 134 134 135 135 136

Dehydration in athletes alters cardiovascular and thermoregulatory function and may inhibit endurance exercise capacity if fluid loss exceeds 2% of bodyweight (BW). If this level of dehydration cannot be prevented when starting from a state of euhydration, then athletes may create a state of hyperhydration by consuming extra fluid prior to exercise. From this hyperhydrated situation, individuals have a greater capacity to tolerate fluid loss before becoming dehydrated. Furthermore, excess pre-exercise fluid intake enhances thermoregulatory ability, as well as increasing plasma volume to maintain cardiac output. However, hyperhydrating before exercise is difficult, because a large fluid intake is typically accompanied by diuresis. Glycerol-containing beverages create an osmotic gradient in the circulation favouring fluid retention, thereby facilitating hyperhydration and protecting against dehydration. Many studies have shown that increases in body water by 1 L or more are achievable through glycerol hyperhydration. This article analyses the evidence for glycerol use in

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facilitating hyperhydration and rehydration, and provides guidelines for athletes wishing to use this compound. An analysis of the studies in this area indicates that endurance athletes intending to hyperhydrate with glycerol should ingest glycerol 1.2 g/kg BW in 26 mL/kg BW of fluid over a period of 60 minutes, 30 minutes prior to exercise. The effects of glycerol on total body water when used during rehydration are less well defined, due to the limited studies conducted. However, ingesting glycerol 0.125 g/kg BW in a volume equal to 5 mL/kg BW during exercise will delay dehydration, while adding glycerol 1.0 g/kg BW to each 1.5 L of fluid consumed following exercise will accelerate the restoration of plasma volume. Side effects from glycerol ingestion are rare, but include nausea, gastrointestinal discomfort and light-headedness. In summary, glycerol ingestion before, during or following exercise is likely to improve the hydration state of the endurance athlete.

Mechanisms that regulate body water are complex. Fluid intake factors such as volume, temperature and composition of ingested fluid, together with gastrointestinal absorption rate, need to be balanced against fluid loss factors such as sweat and renal excretion rates.[1] These can be extensively influenced by environmental conditions, with heat and humidity significantly increasing the rate of fluid loss and altering the distribution of body fluid to aid in heat dissipation.[1] Fluid losses, or shifts between compartments with dehydration, reduce plasma volume and cardiac stroke volume, with concomitant increases in heart rate.[2-4] Peripheral blood supply may be reduced to maintain central blood pressure, leading to a reduction in heat dissipation and increased core temperature.[5,6] These physiological changes may contribute to exertional heatstroke, which may be fatal.[7-9] Furthermore, endurance performance may be impaired when fluid losses exceed approximately 2% bodyweight (BW) during exercise,[10,11] or when subsequent exercise commences when an athlete is still hypohydrated by 2% BW or greater.[12-16] Throughout this review, ‘hyperhydration’ is defined as body water excess beyond normal fluctuations and is characterized by a urinespecific gravity under 1.010.[17] ‘Euhydration’ refers to normal body water and ‘hypohydration’ implies body water deficits beyond normal fluctuations (urine specific gravity over 1.023).[18] Furthermore, ‘dehydration’ refers to losing and ‘rehydration’ to gaining body water. ª 2010 Adis Data Information BV. All rights reserved.

When used predominantly as a preparatory mechanism for subsequent endurance exercise, especially in thermally stressful environments, it is accepted that pre-exercise hyperhydration will delay, prevent or attenuate the effects of dehydration.[19,20] However, ingesting a large bolus of fluid before exercise, even in dehydrated subjects, is typically ineffective at inducing hyperhydration, due to a rapid decrease in antidiuretic hormone (arginine vasopressin), leading to augmented diuresis.[21,22] Therefore, any substance that increases fluid retention before, during or after exercise may have beneficial effects on fluid homeostasis and assist the endurance athlete. Glycerol is a metabolite released during the breakdown of triglycerides, and is distributed in low concentrations throughout all body cells.[23] Its osmotic properties have generated interest in hydration research where the primary focus has been pre-exercise glycerol hyperhydration. Glycerol ingestion with fluid during exercise has also been investigated as a means of attenuating dehydration, while most recently glycerol has been investigated as an agent to assist rehydration. Several previous reviews[23,24] have discussed the pharmacokinetics and mechanisms by which glycerol assists in fluid retention and endurance performance.[25] The primary aim of this review is to provide athletes with specific guidelines for the use of glycerol for pre-exercise hyperhydration, or in beverages consumed during exercise (with and without pre-exercise hyperhydration) and during post-exercise recovery. There are a number of Sports Med 2010; 40 (2)

Guidelines for Glycerol Use

factors that need to be considered when formulating guidelines for athletes wishing to explore the use of glycerol in preparation for exercise. These are discussed with reference to previous studies (table I) that have investigated these issues. To more accurately compare and contrast these studies, they were evaluated using a scale that assessed a number of factors associated with the minimization of bias in areas such as subject selection, performance and data analysis (table II). The results of this process are shown in table III, and more emphasis has been placed on studies with less experimental bias when formulating the guidelines. The scoring system itself was developed using items from a number of extensively evaluated and validated tools[48-51] used to assess the quality of randomized, controlled clinical trials. Items were chosen from those used in the Jadad scoring system,[48] the PEDro scale[49] and the Delphi List,[50] in addition to recommendations contained in the CONSORT statement.[51] Finally, items five and 16 were added because of their perceived importance in studies used to assess exercise performance. It should be noted that the final version of the current scale has yet to be rigorously evaluated and validated on its own merit. From their assessment of construct validity, Jadad et al.[48] indicate that scores of 4/6 and 2/3 on their scales separate the bulk of studies into poor and excellent categories. Based on this, many subsequent studies have used a cut-off of >60% to classify a study as excellent.[52,53] From table III it can be seen that only a few publications contained a high number of important elements. Indeed, only five studies scored >60%, each of which found glycerol hyperhydration to be beneficial. 1. Considerations for Glycerol Use The following sections discuss factors that are fundamental to the use of glycerol in pre-exercise hyperhydration. 1.1 Glycerol Dose

Riedesel et al.[1] investigated the dose-response relationship for glycerol doses of 0.5, 1.0 or ª 2010 Adis Data Information BV. All rights reserved.

115

1.5 g/kg BW. All doses increased water retention; however, the hyperhydration achieved with the 0.5 g/kg glycerol dose was not significantly different from water intake alone. Subsequent analysis supports these findings that glycerol doses higher than 0.5 g/kg BW are required to maximize fluid retention. Robergs and Griffin[23] indicate that a glycerol dose of 1.0–1.5 g/kg BW will be required to elevate plasma glycerol levels to 15 mmol/L. This is the concentration above which blood glycerol levels stabilize, thereby maximizing the osmotic gradient for fluid retention.[23] In the Riedesel et al.[1] study, the level of fluid retention was not further increased following consumption of 1.5 g/kg BW over the 1.0 g/kg BW condition. This disproportion between glycerol dose and fluid retention may have occurred because of the direct relationship between plasma concentration and glycerol catabolism/excretion, which increases glycerol removal from the circulation with higher glycerol doses. Urinary glycerol excretion was doubled and tripled in the 1.5 g/kg condition compared with the 1.0 g/kg condition after 2 and 4 hours, respectively.[1] Consequently, the concentration of glycerol remaining in the body and acting to increase the osmotic gradient to assist in fluid retention was similar between the 1.0 and 1.5 g/kg trials.[1] The top five scoring studies from the quality analysis used glycerol doses of 1.0[35,40] or 1.2 g/kg BW.[34,36,38] All three studies using a dose of 1.2 g/kg BW had fluid retention levels >1 L after 2 hours, compared with 350–500 mL when 1.0 g/kg BW was used. This represents the volume by which total body water is increased above euhydration, which may then be used to convey thermoregulatory and performance benefits. Therefore 1.2 g/kg BW is the recommended dose, which is slightly higher than the average dose of 1.1 g/kg BW given across all pre-exercise hyperhydration studies.[25] 1.2 Volume of Fluid

The total volume of fluid used in glycerol hyperhydration studies ranges from 20 to 29 mL/kg BW. Goulet et al.[25] conducted a meta-analysis on fluid retention associated with glycerol hyperhydration Sports Med 2010; 40 (2)

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Table I. Summary of studies using glycerol in beverages for hyperhydration, during exercise or rehydration Study, year

Subjects

Treatments

Fluid vol with glycerol (mL/kg BW)

Mean total fluid vol (mL)

Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

In GIH, ~780 (55%), 850 (60%), 920 mL (65%) of ingested fluid retained after 120 minutes for 0.5, 1.0 and 1.5 g/kg BW, respectively. GIH fl urine vol through › plasma osmolality, no effect on plasma vol, little additional hyperhydration with 1.5 g/kg compared with 1.0 g/kg, especially after 2 h

No exercise component

Fluid retention ~850 mL (53%) after 120 min. Similar (% fluid retained) to results from 0.5 g/kg glycerol with fluid consumed within 40 min. Indicates little additional benefit from consuming fluid over extended period


Glycerol hyperhydration without exercise Riedesel et al.,[1] 1987 Series I

Riedesel et al.,[1] 1987 Series II

4 M + 3 F, healthy adults

Glycerol Placebo

0.5

21.4

1412

Initial glycerol bolus at time 0, then fluid consumed over 40 min; no exer

H2O with 0.1% NaCl


Glycerol Placebo

1.0

21.4

1412


H2O with 0.1% NaCl


Glycerol Placebo

1.5

21.4

1412


H2O with 0.1% NaCl


Glycerol Placebo

1.0

25.7

1593

Initial glycerol bolus at time 0, with full fluid vol consumed over 210 min; no exer

H2O with 0.1% NaCl

Continued next page

van Rosendal et al.

Sports Med 2010; 40 (2)

Glycerol dose (g/kg BW)

Study, year

Subjects

Treatments




Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

Fruend et al.,[26] 1995

11 M, healthy adults

Glycerol H2O Control

1.5 g/L TBW (= 0.9)

37.0 mL/kg TBW (= 22.2)

1765


H2O (flavoured)

In GIH, ~1250 mL (70%) and ~1200 mL (68%) of ingested fluid retained after 90 and 120 min. GIH fl urine flow rates, fl free H2O clearance rates and › fluid retention (~250 mL at 90 min and ~500 mL at 120 min) vs WIH (p < 0.05). ADH rose (p > 0.05) with glycerol at the same time urine flow and free H2O clearances differed, indicating a possible relationship


Melin et al.,[27] 2002 Koulmann et al.,[28] 2000

8M

Glycerol Control

1.1

21.4

1562


Mineral H2O (0.1% NaCl)

In GIH, ~1200 mL (77%) of ingested fluid retained after 2 h. This half-persisted (~560 mL) a further 90 min later. GIH › plasma osmolality. No effect on renin, aldosterone, ADH or ANP


1.0 initial + 0.1 every h after 2 h

Initial bolus 3.3, 24.7 total in first h, total of 28.4 after 4 h

1729 in 1 hb 1988 after 4 hb

Initial glycerol bolus at time 0, then fluid consumed over 60 min. Exer began 90 min after final fluid intake. Additional glycerol and fluid each h after 2 h

OJ + H2O

In GIH, ~1470 mL (85%) and ~1380 mL (80%) of ingested fluid retained after 90 and 150 min vs ~1300 mL (75%) and ~860 mL (50%) in WIH. GIH fl urine vol before exercise, no effect on haemoglobin, haematocrit or serum

Treadmill walking at 60% . VO2max, with 5 min rest every 30 min (lab based)



Table I. Contd

Pre-exercise glycerol hyperhydration Lyons et al.,[20] 1990a


Glycerol Placebo 1 (large fluid) Placebo 2 (small fluid)

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Continued next page

118


Table I. Contd Study, year

Subjects

Treatments




Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

electrolyte concentrations. GIH › sweat rates, fl rectal temperature during exer 10 M, nonacc

4% CHOelectrolyte drink with 1% glycerol H2O 5% CHOelectrolyte drink

Unknown (estimated at 0.125 g/h over 60 h)

26

1742 initial then encouraged to drink 1 L/h over 60 h

Initial glycerol solution consumed over 90 min, then additional glycerol solution and fluid consumption variable over 60 h; exercise variable over 60 h

Ad libitum 4% CHOelectrolyte drink with 1% glycerol

H2O alone appeared to provide adequate hydration during submaximal exer in simulated desert conditions. Glycerol showed a nonsignificant trend to › sweat rates

Treadmill walking: 3 · 40 min protocols at 4.8 km/h daily (carrying army pack weighing ~16.5 kg) [lab based]

Montner et al.,[30] 1996 Series I

11, endurance trained

Glycerol H2O

1.2 (1.0 initial + 0.2 at 60 min) as 20% solution

26

1749

Initial 20% (5 mL/kg BW) glycerol solution consumed over 30 min, then additional glycerol dose at 60 min mark; total fluid ingestion over 90 min; exer began 60 min after final fluid intake

H2O (aspartameflavoured)

In GIH, ~800 mL (45%) of ingested fluid retained pre-exer (60 min after final fluid consumption) vs ~70 mL in WIH (p < 0.05). Pre-exer urine vol fl 666 mL with GIH vs WIH (p < 0.05). Glycerol ingestion fl heart rate but no effect on rectal temperature. GIH › endurance time (p < 0.05) in both Series I and Series II

Cycle to exhaustion at 61% Wmax (lab based)

Montner et al.,[30] 1996 Series II

5 M + 2 F, endurance trained

Glycerol H2O

1.2 (1.0 initial + 0.2 at 60 min)

26 + 3 every 20 min during exercise

1749 + 605.6 mL/h during exercise

Same pre-exer hyperhydration regimen as for Series I.


The additional fluid consumed during exer prolonged endurance

Cycle to exhaustion at 61% Wmax (lab based)

Continued next page

van Rosendal et al.

Sports Med 2010; 40 (2)

Meyer et al.,[29] 1995

Study, year

Subjects

Treatments




Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

time in both GIH & WIH trials

Additional fluid (CHOelectrolyte solution) consumed during exer

8 M, endurance trained, heat-acc

Euhydration (control) Glycerol Glycerol + rehyd H2O H2O + rehyd

~1.0 (1.2 g/kg LBM)

~24.1 (29.1 mL/kg LBM); additional fluid consumed during exer

1862

Initial glycerol bolus at time 0, then fluid consumed over 30 min; exer began 30 min after final fluid intake


No difference in physiological or thermoregulatory responses between treatments, no difference in total urine vols between GIH & WIH

Treadmill walking at 1.56–1.65 m/s at 4–9% grade . (= 45% VO2max) [lab based]

Latzka et al.,[32] 1998


Euhydration (control) Glycerol H 2O

~1.0 (1.2 g/kg LBM)

~24.1 (29.1 mL/kg LBM)

1862

Initial glycerol bolus at time 0, then fluid consumed over 30 min; exer began 30 min after final fluid intake


No differences between GIH and WIH for › total body water. No difference in physiological or thermoregulatory responses between treatments. Glycerol › endurance time 14.5% compared with control (33.8 vs 29.5 min). Both GIH and WIH fl heart rate over control

Treadmill walking to exhaustion at 1.56–1.65 m/s at 4–9% grade wearing chemical protective clothing (~55% . VO2max) [lab based]

Hitchins et al.,[33] 1999


Glycerol Placebo

1.0

22

1628

Glycerol solution consumed over 30 min; exer began 120 min after final fluid intake

Diluted CHOelectrolyte solution

In GIH, ~650 mL (48%) and 500 mL (38%) of ingested fluid retained after 90 and 120 min. GIH ingestion › fluid retention by 250 mL (90 min) and 600 mL

Cycle for 30 min fixed power output, + 30 min self-paced variable power output (lab based)

Continued next page

119

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Latzka et al.,[31] 1997



Table I. Contd

120



Subjects

Treatments




Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

(120 min) vs WIH (p < 0.05), › performance by 5% in variable workload phase 4M + 2 F

Glycerol pre+ 5% glucose during exer; Glycerol pre+ 0.5% glycerol, 5% glucose during exer; Glycerol pre+ 1.5% glycerol, 5% glucose during exer; H2O pre- + 5% glucose during exer

1.2 (1.0 initial + 0.2 at 60 min)

26

1768

Initial glycerol solution consumed over 30 min, then additional glycerol dose at 60 min mark. Total fluid ingestion over 120 min from the start of the glycerol solution intake; exer began immediately after final fluid intake

H2O

In GIH, ~1000 mL (57%) of ingested fluid retained after 2 h. Fluid retention › with GIH vs WIH (~600 mL; p < 0.05), serum osmolality › with glycerol, no effect on ADH. Continued glycerol ingestion during exercise › stroke vol, fl heart rate

Semirecumbent cycling at 44% . VO2max for 110 min (lab based)

Anderson et al.,[35] 2001

6 M, endurance trained

Glycerol H2O

1.0

20 + CHOelectrolyte drink during exercise

1440


Low joule cordial mixed with H2O

In GIH, ~350 mL (25%) of ingested fluid retained after 2 h. GIH fl pre-exercise urine vol vs WIH (~400 mL; p < 0.05), › forearm blood flow, fl heart rate during exercise, fl rectal temperature late in exercise, fl skin temperature late in exercise, fl ANP, › performance by 5%

Cycle at 98% LT for 90 min, followed by max effort for 15 min (lab based)

Continued next page

van Rosendal et al.

Sports Med 2010; 40 (2)

Montner et al.,[34] 1999a

Subjects

Treatments




Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

Coutts et al.,[36] 2002


Glycerol Placebo

1.2

25

1955



In GIH, ~920 mL (47%) of fluid was retained after 2 h on the warm day and ~1080 mL (55%) on the hot day. GIH › fluid retention 350 mL ( › plasma vol, fl urine) vs WIH (p < 0.05). Glycerol reduced the › in completion time between hot and warm conditions for ODT, no difference in sweat rates

ODT (1.5 km swim, 40 km cycle, 10 km run) [field based]

Magal et al.,[37] 2003


Three phases (i) 1.0 per trial: (ii) – (i) hyperhydration (iii) 0.5 with/without glycerol (ii) dehydration (iii) rehyd with/without glycerol

(i) 22 (iii) 10 (iii) 11

(i) 1703 (iii) 774 (iii) 851

Glycerol solution consumed over 15 min, then fluid consumed over the next 135 min. Exer began immediately after final fluid intake. Additional fluid consumed during exer. During rehyd, glycerol solution consumed over 15 min with total fluid consumption over 90 min

(i) H2O (flavoured) (ii) CHOelectrolyte solution (iii) H2O (flavoured)

In GIH, ~1100 mL (65%) of ingested fluid retained after 2.5 h. GIH › fluid retention ( fl urine production by ~900 mL) vs WIH (p < 0.05), › plasma vol (~7%), no performance benefits

Specific skill and agility tests followed by 75 min tennis match (field based)

Continued next page

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Study, year



Table I. Contd

122


Table I. Contd Subjects

Treatments




Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

Marino et al.,[38] 2003


Glycerol Placebo

1.2

21

1655

Glycerol solution consumed over 150 min; exer began immediately after final fluid consumption

Concentrated OJ mixed with H2O

In GIH, ~1350 mL (82%) of ingested fluid retained after 2.5 h. GIH fl urine output (~118 mL) vs WIH (p < 0.05), › % change in blood vol after 60 min, › heart rate during high-intensity efforts, › sweat rates. No difference between trials for total distance cycled, rectal temperature, mean skin temperature, power produced, perceived exertion, lactate or glucose

Cycle 60 min with aim to complete greatest distance possible. 1 min sprints at 10, 20, 30, 40, 50, 60 min marks (lab based)

Wingo et al.,[17] 2004


H2O + glycerol pre- + H2O during exer H2O prebut not during exer; H2O pre+ during exer;

1.0

2.8% BW

2153 (+ up to 1200 mL per 10mile loop (3600 mL total ad libitum)c


H2O (flavoured)

In GIH, ~1350 mL (63%) of ingested fluid retained after 130 min. GIH fl pre-exercise urine vol (~200 mL) vs WIH (p < 0.05), fl post-exer thirst, fl dehydration postexercise, fl postexercise environmental symptoms questionnaire score, fl time for final 10 miles by 5 min (p > 0.05); heart rate and rectal temperature not altered during exercise

3 · 10 mile loop mountain bike race (8 min break between loops) [field based]

Continued next page

van Rosendal et al.

Sports Med 2010; 40 (2)

Study, year

Subjects

Treatments




Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

Goulet et al.,[39] 2006


Glycerol H2O

1.2

26 mL/kg BW before exer + 500 mL/h during exer

1781 + 830 during exer

Glycerol and fluid intake over 110 min (glycerol solution given at 0, 40 and 80 min marks, H2O given at 20 and 60 min marks); exer began 10 min after final fluid consumption


GIH › TBW ~800 mL (45% of ingested fluid) after 110 min. GIH fl urine production by 271 mL pre-exercise (not significant) and 246 mL during exercise (p < 0.05) vs WIH. No effect on sweat rate, rectal temperature, perceived exertion, endurance performance (time to exhaustion) or peak power output

Cycle at 65% . VO2max for 120 min, followed by 5 min break then an incremental cycle to exhaustion (lab based)

Easton et al.,[40] 2007


Placebo/glycerol Placebo/placebo Creatine/glycerol Creatine/placebo

1.0

~28.6/dayb

2000 mLd

On day of trial, glycerol solution consumed over 60 min, then additional fluid over the next 180 min; further 60 min until exer begand

H2O

GIH › H2O retention vs WIH by 500 mL in placebo trial & by an additional 240 mL in creatine trial (p < 0.05). Glycerol fl heart rate, rectal temperature and perceived exertion. No performance benefit

Cycle at 63% Wmax for 40 min, followed by 16.1 km (10 mile) time trial (lab based)

Nishijima et al.,[41] 2007 Experiment 1

10 M, healthy adults

Glycerol 1 Glycerol 2 Placebo

1.2

25

1651

Placebo and glycerol 1 solution (glycerol mixed in the full vol of fluid) consumed over 60 min. Glycerol 2 was


In GIH, ~600–800 mL (36–48%) of ingested fluid retained after 3 h. GIH 1 fl urine vol by 671 mL vs WIH (p < 0.05). GIH 2 fl urine vol by 843 mL vs WIH (p < 0.05) but GIH 1 & GIH 2 were not

No exer component

Continued next page

123

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Study, year



Table I. Contd

124



Subjects

Treatments




Hydration regimen

Fluid with glycerol

6 middledistance runners

Glycerol Placebo

1.2

Dini et al.,[42] 2007a

14 M, national level oarsmen

Glycerol pre+ H2O during exer Glycerol pre+ glycerol during exer H2O pre- + H2O during exer

1.0 pre28.5 pre- + 4.5 during exer + 1.0 during exer

25

Exercise protocol

significantly different (p > 0.05)

1.0 g/kg BW glycerol in 8 mL/kg BW fluid bolus within 30 min, then additional fluid over the next 60 min (with additional glycerol 0.2 g/kg BW ingested with fluid 60 min after starting hydration) Nishijima et al.,[41] 2007 Experiment 2

Major findings

Placebo solution consumed over 90 min. Glycerol was the glycerol 2 protocol from experiment 1


In GIH, ~850 mL (51%) of ingested fluid retained after 3 h. GIH › BW by 790 mL vs WIH (p < 0.05), and › average power by 9% (p > 0.05) vs WIH

Cycle for 40 min fixed power output, + 30 min self-paced variable power output (lab based)

2500 pre- + 400 during exer

Pre-exercise glycerol solution consumed over 90 min, then 180 min until exer began. Additional 2 · 200 mL solutions consumed at ~30 and 60 min marks during exer

H2O

Following the exercise test, fluid retention › 630 mL in GIH compared with WIH (p < 0.05). Glycerol to the rehydration beverages during exercise significantly fl fluid loss (~300–525 mL), and improved work capacity at the anaerobic threshold, compared with both of the other hydration regimens

89 min rowing protocol: 6 · 3 min blocks, with 1 min rest between each, starting at 250 W and › to 400 W in 30 W increments; repeated 3 times with 15 min break between each (lab based)

Continued next page

van Rosendal et al.

Sports Med 2010; 40 (2)

1651

Study, year

Subjects

Treatments




Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

Goulet et al.,[43] 2008


Glycerol Control (euhydration)

1.2

26 pre- + 12.5 during exer

1776 pre- + 853 during exer

At 0 and 20 min, subjects drank 9 and 6 mL/kg BW fluid, each with 0.6 g/kg BW glycerol, then drank 6 mL/kg BW H2O at 40 and 60 min marks; further 30 min until exercise


In GIH, ~1100 mL (62%) of ingested fluid retained 30 min after final fluid consumption. Glycerol › endurance time and peak power and fl HR and thirst. No effect on rectal temperature (tended to stay lower with glycerol), sweat rate, thermal stress or RPE

Cycle for 120 min at 65% . VO2max with 5 · 2 min intervals at 80% . VO2max performed at 12, 32, 52, 72 and 92 min marks); then incremental test to exhaustion (lab based)



Table I. Contd

Glycerol consumption during exercisea 4 M + 5 F, healthy adults

H2O 10% glycerol; 6% CHO; 6% CHO + 4% glycerol

~0.94 (1.2 g/kg LBM)

3/kg LBM

647

Glycerol solution consumed over initial 60 min of exer

CHOelectrolyte solution

Glycerol fl the % change in plasma vol and fl overall mean ratings of perceived thirst but no substantial urine, metabolic, hormonal, cardiovascular or thermoregulatory advantages to the consumption of solutions containing 4% or 10% glycerol during exercise

Cycle at 51.8% . VO2peak for 90 min (lab based)

Siegler et al.,[45] 2008e

10 M, experienced soccer players

Glycerol (5.2% solution) Placebo

~0.7

13.4

1000

500 mL of glycerol or placebo solution consumed within 30 min before training, then a further 500 mL consumed after 30 min of training

CHOelectrolyte solution

Glycerol solution attenuated the drop in plasma vol and BW during the training session. No effect on HR during exercise or fatigue test

Variable intensity training drills followed by intermittent endurance test (field based)

Continued next page

125

Sports Med 2010; 40 (2)

Murray et al.,[44] 1991

126



Subjects

Treatments




Hydration regimen

Fluid with glycerol

Major findings

Exercise protocol

Glycerol use in rehydrationf Scheett et al.,[46] 2001

8 M, non-acc

Glycerol Placebo

1.0

3% BW (100% fluid lost during dehydration)

2487

Glycerol solution consumed over initial 30 min, then fluid consumed over the next 150 min; exer began immediately after final fluid consumption

1st 30% aspartameflavoured H2O, remaining 70% H2O

Glycerol ingestion fl urine production, › plasma vol and BW restoration, better rehyd index with glycerol. Also, fl rectal temperature (but no thermoregulatory benefits) and significantly longer exer time to exhaustion (12.6%) with glycerol

Cycle to exhaustion at . 50% VO2peak, cadence 60 rpm (lab based)

Kavouras et al.,[21] 2005


Glycerol H2O No fluid

1.0

3% BW (75% of fluid lost during dehydration)

2103

Glycerol solution consumed over initial 15 min, then fluid consumed over the next 80 min; exer began 30 min after final fluid consumption

1st 1/3 (glycerol solution) aspartameflavoured H2O, remaining 2/3 was plain H2O

Plasma vol › more and remained higher with glycerol, cutaneous vascular conductance was › with glycerol but no other thermoregulatory mechanisms. No effect on fluid-regulating hormones with glycerol. Glycerol ingestion significantly › time to exhaustion (18%)

Cycle to exhaustion at . 74% VO2peak, cadence 80–100 rpm (lab based)

a

Lyons et al.,[20] Montner et al.[34] and Dini et al.[42] also gave glycerol during exercise following glycerol-induced hyperhydration.

b

Assuming average 70 kg subjects.

c The full 1200 mL of fluid was consumed at the end of the loop on only three occasions out of the 72 trials. Average fluid consumed ranged from 693 mL to 842 mL across the trials. Average total fluid consumed was 4458 mL for water trial, 4643 mL for glycerol trial and 2240 mL for no fluid during exercise trial. Easton et al.[40] 2 · 500 mL daily of treatment solution for 6 days pre-trial + 500 mL of treatment solution with 2 · 500 mL H2O on day of trial. Siegler et al.[45] also gave 500 mL of glycerol solution before exercise.

f

Magal et al.[37] also gave glycerol during rehydration following hyperhydration and dehydration in their three-part study.

ADH = antidiuretic hormone; ANP = atrial natriuretic peptide; BP = blood pressure; BW = bodyweight; CHO = carbohydrate; exer = exercise; F = females; GIH = pre-exercise glycerol hyperhydration; H2O = water; heat-acc = heat acclimated; HR = heart rate; lab = laboratory; LBM = lean body mass; LT = lactic threshold; M = males; non-acc = non-heat acclimated; ODT = Olympic distance triathlon (1.5 km swim, 40 km bicycle, 10 km run); OJ = orange juice; rehyd = rehydration; RPE = rating of perceived exertion; rpm = revolutions per minute; . TBW = total body water; VO2max = maximum oxygen consumption; vol = volume; WIH = pre-exercise water hyperhydration; Wmax = reported as maximal workload; › indicates increase; fl indicates decrease.

van Rosendal et al.

Sports Med 2010; 40 (2)

d e


127

Table II. Scale to evaluate original investigations for factors associated with the minimization of bias in selection of subjects, performance and analysis of resultsa 1

A clear description of the inclusion and exclusion criteria was provided

Yes &

No/not sure &

NA &

2.

The trials were randomized

Yes &

No/not sure &

NA &

3.

The method used to generate the random allocation sequence, including details of any restrictions (e.g. blocking, stratification) was described

Yes &

No/not sure &

NA &

4.

Sample size was justified (e.g. by power calculation)

Yes &

No/not sure &

NA &

5.

Attempts were made to control and/or monitor pre-trial conditions (e.g. diet, exercise)

Yes &

No/not sure &

NA &

6.

Design incorporated measures of important baseline variables

Yes &

No/not sure &

NA &

7.

There was blinding of all subjects

Yes &

No/not sure &

NA &

8.

There was blinding of all investigators involved in the trials

Yes &

No/not sure &

NA &

9.

Both the method of blinding and the evaluation of the successfulness of blinding were described

Yes &

No/not sure &

NA &

10.

Details were provided regarding the inability of a subject to complete study requirements

Yes &

No/not sure &

NA &

11.

Statistical methods used to compare groups for primary outcome measure(s),b and methods for additional analyses, such as subgroup analyses and adjusted analyses, were described

Yes &

No/not sure &

NA &

12.

Both point measures and measures of variability for the primary outcome measure(s)a were provided

Yes &

No/not sure &

NA &

13.

The results of between-group statistical comparisons were reported for the primary outcome measure(s)b [e.g. an estimated effect size], and its precision (e.g. 95% CI)

Yes &

No/not sure &

NA &

14.

The method used to assess adverse effects was described

Yes &

No/not sure &

NA &

15.

Reproducibility of the primary outcome measure(s)b was reported

Yes &

No/not sure &

NA &

16.

If a performance test was used, a familiarization trial was conducted

Yes &

No/not sure &

NA &

a

Scoring: the final percentage score is determined by dividing the number of ‘yes’ scores by total number of applicable items (16 minus the number of NA items).

b

If primary outcome measure not stated then key measure used.

NA = not applicable.

and found that a fluid volume of 26 mL/kg BW would maximize fluid retention. The current recommendations will therefore be based upon this volume. Two other studies have investigated the inclusion of glycerol with common pre-exercise hydration regimens.[45,54] While these are not specifically categorized as pre-exercise hyperhydration studies because of the small total fluid intake, they do provide a practical application for athletes. The first study investigated glycerol (1.0 g/kg BW) consumption with a typical pre-race fluid intake.[54] There were no hydration or performance benefits, most likely due to the smaller total fluid intake (1250 mL) combined with the bulk of the fluid being ingested 4 hours before exercise, allowing considerable time for fluid to be cleared by the kidneys before exercise commenced.[54] However, when consuming 500 mL of a glycerol ª 2010 Adis Data Information BV. All rights reserved.

solution within the 30 minutes preceding a 60-minute training session, and another 500 mL half way through training, Siegler et al.[45] showed that glycerol solutions can attenuate the BW and plasma volume losses during exercise. Thus, if an athlete is unable to tolerate the large volumes of fluid (26 mL/kg BW) and glycerol required to induce pre-exercise hyperhydration, then they may consider consuming smaller volumes of fluid and glycerol closer to the commencement of activity. 1.3 Type of Fluid

Carbohydrate-electrolyte beverages (sports drinks) may provide better hydration potential than water alone during prolonged endurance exercise.[55,56] The major factors affecting the absorptive potential of fluids include: type and concentration of carbohydrate, solution osmolality, Sports Med 2010; 40 (2)

128


Table III. Evaluation of the studies investigating glycerol use for pre-exercise hyperhydration and for rehydration during and after exercise Stats Data Eligibility Randomizationa,b Power Pre-trial Baseline Blindingc,d,e NonAdverse Reproducibility Familiarization reported performance calc. conditions measures completers described reportingf,g effects test described described

% score Reference

Pre-exercise hyperhydration 1

1a

0

0

1

0

NA

0

2f,g

0

0

NA

29

1

0

1

a

0

0

1

0

NA

1

2f,g

0

0

NA

36

20

0

1

a

0

0

1

1

1

1

2

f,g

0

0

1

50

29

0

0

0

1

1

2c,d

NA

1

2f,g

0

1

NA

57

26

0

0

0

1

0

0

NA

1

2f,g

0

0

NA

29

47

f,g

c

c

0

0

0

1

0

1

NA

1

2

0

0

NA

36

47

0

1a

0

1

1

2c,d

NA

1

1f

0

0

0

47

30

0

1a

0

1

1

2c,d

NA

1

1f

0

0

0

47

30

0

1

a

1

2

c,d

1

1

2f,g

0

0

0

56

31

1

1

a

0

1

1

2

c,d

NA

1

2

f,g

0

0

0

60

32

0

1a

1

1

0

2c,d

NA

1

2f,g

0

1

NA

64

34

0

0

0

1

1

2c,d

NA

1

2f,g

0

0

1

53

33

0

2a,b

0

1

1

3c,d,e

NA

1

2f,g

1

0

0

73

35

0

1

a

1

c,d

NA

1

2f,g

1

0

1

67

36

0

1

a

0

1

0

0

NA

1

2

f,g

0

0

NA

36

27

0

1a

0

1

1

3c,d,e

NA

1

2f,g

0

1

1

73

38

0

1a

0

1

1

2c,d

NA

1

2f,g

0

0

1

60

37

0

1

a

0

0

1

2

c,d

NA

1

2f,g

0

0

0

47

17

0

1a

0

1

1

2c,d

NA

1

2f,g

1

0

0

60

39

1

1

a

0

1

1

3

1

1

2

f,g

0

1

1

81

40

0

1a

0

1

1

2c,d

0

1

2f,g

0

0

0

50

41

0

1

a

0

1

0

0

NA

1

2

f,g

0

0

0

33

42

0

1a

0

1

1

0

NA

1

2f,g

1

1

0

57

43

0

0

1

1

2

c,d,e

0

0

0

1

1

1c

NA

1

2f,g

1

0

1

53

44

0

1a

0

1

1

2c,d

NA

1

2f,g

0

0

1

60

45

Continued next page

van Rosendal et al.

Sports Med 2010; 40 (2)

Glycerol during exercise


Reporting group comparisons (item 13).

f

g

calc. = calculation; NA = not applicable; stats = statistics.

Blinding described (item 9).

Reporting point measures (item 12).

e

Blinding of subjects (item 7).

Blinding of investigators (item 8). d

Randomization described (item 3).

c

Randomization (item 2).

b

129

a

21

46

Scoring: Each column, except the randomization, blinding and data reporting columns, have a maximum score of 1 point. The randomization column has a maximum score of 2 points as it combines items 2 and 3 from table II. The blinding column has a maximum score of 3 points as it combines items 7, 8 and 9 from table II. The data reporting column has a maximum score of 2 points as it combines items 12 and 13 from table II. The following denotes which specific criteria were fulfilled for the columns combining more than 1 item:

60

53 0

0 0

0 0

0 2f,g 1 NA 2 1 1 0 1 1

2f,g 1 NA 2c,d 1 1 0

c,d a

1a 0

Glycerol during rehydration

Baseline Blindingc,d,e NonAdverse Reproducibility Familiarization Eligibility Randomizationa,b Power Pre-trial Stats Data calc. conditions measures completers described reportingf,g effects reported performance described described test

Table III. Contd

% score Reference


pH, electrolyte concentration, volume of fluid and palatability (flavour, temperature, colour).[56] Given that glycerol alters the osmolality and caloric density of solutions it is dissolved in, it is also pertinent to understand the effect it will have on fluid absorption. Two studies have demonstrated that glycerol may provide a pro-absorptive effect, evidenced through enhanced intestinal water and sodium absorption in rat intestinal perfusion models.[57,58] Wapnir et al.[58] found that glycerol solutions attenuated water secretion into the perfused segment of the small intestine and significantly reduced the outflow of sodium into the lumen, when compared with sports drinks without glycerol. Furthermore, glycerol solutions had a higher influx-to-efflux ratio resulting in a net influx of water (from the intestinal lumen to the circulation), while glucose solutions had a lower influx-to-efflux ratio resulting in a net efflux of water (into the intestinal lumen).[58] Allan et al.[57] tested the absorption of oral rehydration solutions containing 0.75 mmol/L sodium and the following combinations of glucose : glycerol: 75 : 0, 50 : 25, 37.5 : 37.5, 25 : 50, 10 : 65 and 0 : 75 (mmol/L). Substituting glycerol for glucose enhanced both net sodium and water absorption in rat perfusion models, with peak absorption of both sodium and water occurring with the glucose : glycerol ratio of 25 : 50. Thus, the combination of glycerol and glucose enhanced absorption of fluid from the intestinal lumen to the circulation compared with the solution containing glycerol without glucose, and vice versa.[57] While further investigation in humans is required, the similarity of the physiological process associated with sodium and water movement from the intestinal lumen in rats and humans suggests that the results from these trials can be applied to humans with some confidence,[58] although a published abstract indicates that this may not be the case.[59] In addition, the inclusion of sodium in sports drinks might improve gastrointestinal glucose and fluid absorption,[56] and offer some protection against hyponatraemia. Hyponatraemia typically results from over-hydration with hypotonic fluids during exercise (i.e. drinking water and losing sodium in the sweat).[60-63] The risk of Sports Med 2010; 40 (2)

van Rosendal et al.

130

hyponatraemia is very high when so much fluid is consumed that weight gain during exercise exceeds 2.5% BW.[63,64] It has been advocated that drinking sports drinks containing high levels of sodium during prolonged (>2 hours) exercise may help to stabilize the sodium content of the extracellular fluid and assist in the prevention of hyponatraemia.[65-67] One proposed negative effect of drinking sports drinks prior to exercise is the possible development of hypoglycaemia. However, a recent series of experiments showed that glucose (75 g) consumed 45 minutes prior to exercise resulted in the stabilization of plasma glucose at a level that was not considered hypoglycaemic and was unaffected by exercise intensity.[68] Subsequent trials showed that rebound hypoglycaemia was (i) more evident following glucose ingestion when compared with carbohydrates with a lower glycaemic index;[69] (ii) equally evident following glucose doses of 25, 75 and 200 g;[70] and (iii) more evident when glucose was consumed longer before exercise (75 > 45 > 15 minutes).[71] However, in all of these conditions, hypoglycaemia was only present for the initial 10–20 minutes during steady-state exercise and had no negative effects on subsequent time trial performance lasting approximately 40 minutes.[69-71] Hargreaves et al.[72] have stated that if ingesting carbohydrate pre-exercise, then a reasonable amount (100 g) should be consumed to provide a supply of glucose later in exercise to offset the suppression of fat oxidation. Most glycerol hyperhydration studies have used aspartame-flavoured water as the hyperhydrating beverage and have consistently induced hyperhydration. Given the rationale that carbohydrate-electrolyte drinks may provide a better hydration potential than water alone, as well as providing sodium to attenuate hyponatraemia, it could also be proposed that consuming carbohydrate-electrolyte beverages with glycerol could further enhance the hyperhydration benefits of glycerol. 1.4 Timing of Fluid with Glycerol

Two different fluid ingestion protocols are used to promote pre-exercise hyperhydration. ª 2010 Adis Data Information BV. All rights reserved.

The first involves quickly ingesting a small concentrated bolus of glycerol solution, then consuming the remaining fluid over a longer duration. The second involves mixing the glycerol within the full volume of fluid, thereby ingesting glycerol with fluid throughout the pre-exercise hyperhydration period. Study methodologies differ greatly in the duration over which these fluids are provided, making it difficult to determine the optimal protocol for fluid consumption relative to glycerol intake. Table I provides details of different protocols used. One study investigated the difference between these styles of fluid and glycerol delivery and found that the change in bodyweight and urine volume were similar with either mode.[41] However, the results might be confounded by the fact that the duration over which fluids were consumed was longer in the glycerol bolus trial (90 vs 60 minutes).[41] Thus, the optimal period for fluid consumption in relation to the glycerol bolus intake also needs to be considered. The second protocol used in the abovementioned study by Riedesel et al.[1] provided the glycerol bolus that was optimal in the first series of trials (1.0 g/kg BW), with a larger volume of fluid (25.7 mL/kg BW of 0.1% NaCl solution) over a longer duration (3.5-hour period). This fluid regimen reduced hyperhydration to a level similar to the ingestion of 0.5 g/kg BW of glycerol and fluid within 40 minutes (21.4 mL/kg BW of 0.1% NaCl solution) used in the first protocol. However, others have used similar methods with much greater success.[28,37] Mixing the glycerol through the entire hyperhydration beverage in order to spread the glycerol consumption over a longer period also results in fluid retention.[17,38,41] However, these longer protocols tend to measure hyperhydration immediately after fluid ingestion is completed, while the shorter fluid intakes tend to measure hyperhydration after lengthy equilibration periods. It is not surprising that the percentage of fluid retained is higher if you measure immediately after fluid consumption. Of the five studies scoring highest in the quality assessment, glycerol and fluid were given over 15,[35] 60,[36] 120,[34] 150[38] or 300 minutes.[40] Fluid retention Sports Med 2010; 40 (2)


was greatest when glycerol and fluid was ingested over 60–150 minutes. Noakes et al.[73] highlighted the importance of gastric volume in regulating gastric emptying. Briefly, the maximum rate at which fluid can be delivered from the stomach is significantly influenced by the volume of fluid in the stomach, and therefore by the rate of fluid consumption.[73] The data from Noakes et al. indicate that the rate of water delivery from a 7% carbohydrate solution will be approximately 400 mL per 10 minutes if a gastric volume of approximately 800 mL is maintained.[73] Therefore, an individual should aim to consume 600–800 mL within about 10 minutes of starting the hydration period, and then a further 400 mL each 10- to 15-minute period during the next 50 minutes. This will result in a volume of fluid equal to 26 mL/kg BW (approximately 1820 mL for a 70 kg individual) being consumed within 60 minutes and absorbed within approximately 90 minutes from the onset of fluid intake. If an individual is unable to stomach volumes of this magnitude, then a smaller volume of fluid should be consumed in each 10-minute period, focusing on drinking the fluid as rapidly as possible. 1.5 Duration of Hyperhydration

Glycerol ingestion has been associated with hyperhydration for periods of up to 4 hours.[1,17,20,26,30,33,35-38,74] Peak hyperhydration is determined by the relationship between glycerol and fluid absorption, and clearance. It is difficult to determine when peak hyperhydration occurs, because the timing of measurements of fluid retention varies greatly between studies. Several studies have mapped fluid retention for periods of up to 3 hours after ingestion, without the confounding of an exercise protocol beginning within this period. After 2 and 3 hours, 60–80%[1,20,26] and 45–60%,[1,20,26] respectively, of the ingested fluid was still retained in the glycerol trial (compared with 40–60% and 10–30%, respectively, in the water hyperhydration trial).[26] Because the absorption of a large volume of fluid will occur rapidly when fluid intake is rapid (as discussed in section 1.4),[73] exercise should ª 2010 Adis Data Information BV. All rights reserved.

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commence 30 minutes after final fluid consumption. Waiting for an extended period will result in unnecessary water loss and reduce overall hyperhydration. Waiting 30 minutes after fluid intake should allow sufficient time for the sensation of stomach fullness to subside, while ensuring that exercise begins when hyperhydration is close to maximal. It has been demonstrated that it is possible to maintain hyperhydration using glycerol for up to 49 hours.[47] For prolonged hyperhydration, water needs to be consumed at either the same or a greater rate than it is lost. Glycerol may assist in this process by decreasing water loss. However, during this time, glycerol would also need to be ingested at rates in excess of its rate of catabolism/ excretion. Although the study by Koenigsberg et al.[47] has demonstrated prolonged hyperhydration with glycerol, until further research into sustained hyperhydration (i.e. >4 hours) is completed, the authors would strongly advise against this practice, as it will theoretically increase the risk of hyponatraemia. Whether this could be overcome by using a carbohydrate-electrolyte beverage has not been studied (see section 4). 1.6 Guidelines for Pre-Exercise Glycerol Hyperhydration

Pre-exercise glycerol hyperhydration will be most advantageous when sweat losses cannot be replaced during exercise. However, if euhydration can be maintained during exercise, then preexercise hyperhydration may not provide any additional advantage. If an athlete commences exercise in a hyperhydrated state, they must ensure that they do not over-drink during exercise. The additional fluid retained with pre-exercise hyperhydration will act to dilute plasma sodium before commencing exercise. If additional large volumes of hypotonic fluid are consumed during exercise, there exists an increase in the potential risk of dilutional hyponatraemia.[18] Given the hypotonic composition of sweat, the extra fluid stored with pre-exercise hyperhydration may be lost during exercise without a concomitant increase in the loss of sodium, assuming that aggressive fluid intakes are not made during exercise. In addition, Sports Med 2010; 40 (2)

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Table IV. Guidelines for glycerol and fluid ingestion to promote preexercise glycerol hyperhydration Only undertake a pre-exercise glycerol hyperhydration protocol if the exercise is likely to induce a reduction in bodyweight (BW) >2% Consume a glycerol dose of 1.2 g/kg BW with a volume of fluid equal to 26 mL/kg BW. If this volume is too high for an individual, then consider personalizing the protocol by consuming a smaller volume of fluid and glycerol closer to the commencement of activity Consume the glycerol solution over a period of 60 min Use the normal choice of beverage. Carbohydrate-electrolyte beverages with a relatively high sodium content might provide an additional advantage, however this requires further investigation Commence exercise approximately 30 min after the total hyperhydration fluid volume has been consumed Consider the increased metabolic cost associated with undertaking weight-bearing exercise with elevated BW

the increased chance of having to void during competition should be considered.[18] From the preceding sections, guidelines for glycerol and fluid ingestion to establish preexercise hyperhydration have been formulated and are presented in table IV. 2. Glycerol Ingestion during Exercise The goal of ingesting fluid during exercise should be to replace enough of the fluid lost as sweat to avoid incurring a fluid deficit of >2% BW and/or an electrolyte imbalance that may lead to hyponatraemia.[18] The volume of fluid to be consumed will therefore depend on the sweat rate during the activity. This is determined by the mode and intensity of exercise, the environmental conditions, exercise duration and individual variation.[18] However, guidelines for glycerol consumption during exercise will also depend upon whether the athlete has hyperhydrated preexercise, as this will delay the body water deficit reaching 2% BW. The following sections discuss the use of glycerol during exercise based on whether pre-exercise hyperhydration has taken place. 2.1 Glycerol Ingestion during Exercise, after Pre-Exercise Hyperhydration

Glycerol pharmacokinetics indicate that only small additional doses during exercise are needed to maintain elevated plasma glycerol levels for several hours, when pre-exercise hyperhydraª 2010 Adis Data Information BV. All rights reserved.

tion has been undertaken. For example, when a glycerol dose of 1.2 g/kg BW is used to hyperhydrate pre-exercise, plasma glycerol levels should be elevated to saturation kinetics for around 3 hours.[75] Glycerol will then be half eliminated approximately 140 minutes later,[23,75] although this will be more rapid if exercise begins 30 minutes after fluid ingestion, due to increased metabolism. Three studies have investigated glycerol consumption with fluid during exercise following pre-exercise glycerol hyperhydration (table I).[20,34,42] Montner et al.[34] required subjects to ingest a total of 1.2 g/kg BW of glycerol with water (26 mL/kg BW) pre-exercise in three hyperhydration trials. Subjects ingested a further 5 mL/kg BW every 20 minutes (total 25 mL/kg BW) of solutions containing either (by volume) 5% glucose, 0.5% glycerol (0.125 g/kg BW) in 5% glucose, or 1.5% glycerol (0.375 g/kg BW) in 5% glucose, during 110 minutes of semi-recumbent cycling. While the maintenance of bodyweight during exercise with continual glycerol ingestion was slightly better than with glycerol hyperhydration alone, the benefit was not significant. However, glycerol ingestion during exercise did result in an increased stroke volume and decreased heart rate, indicating improved cardiovascular performance. In support of the above pharmacokinetic data, there was no difference between the 0.5% and 1.5% (0.125 or 0.375 g/kg BW) glycerol solutions.[34] Dini et al.[42] showed that the addition of glycerol to rehydration beverages during exercise significantly increased fluid retention (~525 mL) and improved work capacity at the anaerobic threshold, compared with other hydration regimens. In the Lyons et al.[20] study, the effect of glycerol ingestion during exercise is difficult to establish as no trial existed in which subjects were given glycerol before but not during exercise. Furthermore, no blood samples were taken between the hyperhydration period and the commencement of exercise, so it is impossible to distinguish between the effects of the pre-exercise glycerol bolus and the doses given during exercise. It is recommended that athletes only consume glycerol during exercise if they are going to incur a fluid deficit >2% BW. A 70 kg athlete Sports Med 2010; 40 (2)


(with a total body water volume ~42 L) can lose ~1.4 L of fluid (so that total body water would drop to 40.6 L) in order to reach the ‘dehydration threshold’ of a 2% reduction in BW. However, the extra fluid retained with hyperhydration is also available to be lost as sweat, thereby delaying the progression of dehydration. If the same 70 kg athlete hyperhydrated preexercise by ~900 mL (the average volume retained with pre-exercise glycerol hyperhydration for a 70 kg athlete[25]), then their total body water would increase to approximately 42.9 L. This additional fluid is also available to be lost as sweat before they reach their ‘dehydration threshold’ of a reduction in total body water to 40.6 L. Now the athlete can lose ~2.3 L of fluid (1.4 L + the additional 0.9 L stored through hyperhydration) before reaching the same relative level of dehydration compared with when they are normally euhydrated. Based on a sweat rate of 1.5 L/h, exercise durations of approximately 90 minutes would be needed to achieve this fluid deficit. For continued glycerol ingestion with fluid during exercise following pre-exercise hyperhydration, it is recommended the athlete consume a small amount of glycerol (0.125 g/kg BW) in a volume equal to 5 mL/kg BW when exercise is of sufficient duration to dehydrate them by >2% BW. The specific dose is based on the Montner et al.[34] study, as it scored highly (64%) on the scale of research quality compared with the Dini et al.[42] study (33%). Furthermore, it is imperative that athletes avoid drinking any more fluid than a volume that is sufficient to replace sweat loss, so there is no net weight gain during exercise. Thus, if athletes have hyperhydrated pre-exercise, and exercise duration is £75 minutes, then very little fluid would be needed during exercise, and the consumption of glycerol with any fluid is not recommended. The American College of Sports Medicine’s (ACSM) position stand on fluid replacement also advocates the consumption of beverages containing sodium and/or salted snacks to help stimulate thirst and retain fluids.[18] Carbohydrate in rehydration solutions, while not further facilitating rehydration, may slightly improve the intestinal uptake of sodium and water.[76] Replacement of electroª 2010 Adis Data Information BV. All rights reserved.

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lytes, particularly sodium, is crucial and the inclusion of electrolytes in ingested fluids will help maintain plasma volume.[44,45] 2.2 Glycerol Ingestion during Exercise, without Pre-Exercise Hyperhydration

Athletes starting exercise in a normal euhydrated condition might also benefit from adding glycerol to fluid consumed during exercise, as a means to prevent or delay dehydration by enhancing retention of the ingested fluid. Murray and colleagues[44] are, to our knowledge, the only group to study the specific effects of glycerol on hydration during exercise without any pre-exercise glycerol and fluid ingestion. Siegler et al.[45] gave 500 mL 30 minutes preexercise and a further 500 mL during exercise. The small total volume of fluid consumed (647[44] to 1000 mL[45]) in each of these protocols prohibits them being described as hyperhydration studies. Between them, they provided solutions with glycerol concentrations ranging from 4% to 10% of the fluid volume (4% glycerol with 6% carbohydrate and 10% glycerol;[44] and 5.2% glycerol with 4% carbohydrate[45]). The resulting glycerol doses were 0.38 and 0.94 g/kg BW for the 4% and 10% solutions of Murray et al.[44] and 0.7 g/kg BW for the 5.2% beverage of Siegler et al.,[45] respectively. . Over 90 minutes of cycling at 50% VO2 peak (in 30C, 45% relative humidity environment), both the 4% and 10% glycerol solutions reduced thirst sensation and attenuated the decrease in plasma volume seen with the water placebo and sports drink solutions.[44] From 60 to 80 minutes during exercise the 10% glycerol solution provided better maintenance of plasma volume than did the 4% solution; however, they were similar at all other timepoints. The protocol of Siegler et al.[45] resulted in a 40% reduction in BW loss with the glycerol solution. This reflects equal or improved thermal tolerance in the glycerol trials with less dehydration, as no difference was observed between trials for variables such as core temperature and heart rate. Siegler et al.[45] also showed a 55% reduction in the change in plasma volume over 60 minutes of exercise compared Sports Med 2010; 40 (2)

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with the sports drink. Thus, the addition of glycerol to beverages consumed during exercise has the potential to maintain fluid balance to a greater extent than sports drinks or water alone. Guidelines for glycerol use during exercise need to consider the duration of the event. Glycerol metabolism is relatively slow (~8–9 g/h).[77,78] No studies have investigated the continual ingestion of glycerol during longer (e.g. ultra-endurance) events. However, because glycerol is slowly metabolized, it may be expected that continual administration over prolonged periods (e.g. >4 hours) will lead to an accumulation of glycerol in the circulation resulting in multiple side effects, some of which may be health threatening.[44,45] Therefore, we recommend athletes consume glycerol 0.4 g/kg BW with fluid during each of the first 4 hours of exercise. This would provide a similar dose to that recommended during hyperhydration, with adjustment for increased metabolism with exercise. After this time, individuals should consume fluid alone where necessary. The volume consumed each hour will depend on sweat rate, exercise duration and opportunities to drink.[18,79] For an event such as the marathon, the ACSM recommend that smaller persons exercising at a lower intensity in cooler environments need to replace around 0.4 L/h, and this is increased to 0.8 L/h for heavier individuals exercising at higher intensities in warmer environments.[18] Finally, similar to all guidelines presented here, glycerol use should only be considered when dehydration is likely to exceed 2% BW. Thus, using the example of the 70 kg athlete starting exercise in a normal euhydrated condition (i.e. who hasn’t hyperhydrated pre-exercise), glycerol use is recommended if fluid losses are likely to exceed 1.4 L. Based on a sweat rate of 1.5 L/h, an exercise duration of approximately 60 minutes would be required to achieve this fluid deficit. 2.3 Guidelines for Glycerol Ingestion during Exercise

Guidelines for glycerol ingestion will depend on the extent of dehydration during the activity. Because sweat rates are highly variable, athletes should estimate their sweat rate in conditions simiª 2010 Adis Data Information BV. All rights reserved.

lar to those in which performance will take place, to assist in determining a hydration protocol. To do this, weight loss during a session mimicking typical performance should be monitored and corrected for fluid intake, then divided by the duration of the activity. For simplicity, 1 kg weight loss is considered equal to approximately 1 L of fluid. Glycerol use during exercise is then advocated by following the guidelines in table V. 3. Glycerol as a Rehydrating Agent To date, only three studies have explored the role of glycerol in rehydration (table I).[21,37,46] Most recently, Scheett et al.[46] and Kavouras et al.[21] dehydrated subjects via exercise (by -3% and -4% BW, respectively) before rehydrating (3% BW each) with or without glycerol (1 g/kg BW). The third study to investigate glycerol consumption with rehydration fluid was conducted by Magal et al.,[37] employing a protocol that had three stages: (i) hyperhydration with or without glycerol; (ii) exercise-induced dehydration; and (iii) rehydration with or without glycerol (0.5 g/kg BW).

Table V. Guidelines for the inclusion of glycerol in rehydration fluids given during exercise Glycerol use should be considered when exercise is of sufficient duration to dehydrate by >2% bodyweight (BW) If pre-exercise hyperhydration with glycerol has taken place, then consume 0.125 g/kg BW of glycerol in a volume equal to 5 mL/kg BW Drinking fluid at a rate greater than that required to replace sweat loss (leading to a net weight gain during exercise) should be avoided. Therefore, if an athlete is hyperhydrated before exercise lasting £75 min, very little fluid would be needed during exercise under most conditions, and the consumption of glycerol with any fluid is not recommended If no pre-exercise hyperhydration has taken place, then a larger dose of glycerol with fluid during exercise is warranted. Therefore, we recommend athletes consume 0.4 g/kg BW glycerol with fluid during each of the first 4 h of exercise After 4 h, individuals should consume fluid alone where necessary It is recommended that smaller persons exercising at a lower intensity in cooler environments need to replace around 0.4 L/h, and this goes up to 0.8 L/h for heavier individuals exercising at higher intensities in warmer environments Continual administration of glycerol over prolonged periods (e.g. >4 h) may lead to an accumulation of glycerol in the circulation. As such, continuing glycerol ingestion after 4 h is not advised

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Each of these studies found that beverages containing glycerol were associated with significantly more rapid and complete restoration of plasma volume than water alone. In the Magal et al. study,[37] subjects became dehydrated by -2% and -3% BW for the glycerol and placebo trials, respectively, with corresponding plasma volume changes of -11% and -13%. Following rehydration, plasma volume remained at -4% compared with euhydrated baseline for the water alone trial, but increased to +2% for the glycerol trial. This restoration and expansion of plasma volume to greater than baseline levels in the glycerol trial occurred even though the subjects were still in a state of whole body dehydration (at the end of rehydration, subjects were still -1.5% BW for the glycerol trial and -2.5% BW for the water trial).[37] As such, plasma volume is restored before the interstitial and intracellular fluid compartments.[37] The effect of glycerol on total body water is less defined. In the Magal et al.[37] study, urine volume was higher (by ~50 mL) and percentage fluid retention was lower (~5%) with glycerol compared with water. In the Kavouras et al.[21] study, urine volume was 385 mL lower with glycerol (p > 0.05), and in the Scheet et al.[46] study there was no difference in urine volume between the conditions. However, the influence of glycerol on total fluid retention might be related to rehydration duration. Kavouras et al.[21] and Magal et al.[37] monitored passive rehydration over 80 and 90 minutes, respectively. The data of Scheet et al.[46] indicate that benefits might be more pronounced with longer rehydration periods. In the glycerol trial, approximately 100 mL of urine was produced during each of the 3 hours. In the water trial, 25 symptoms

Mobility Physical activity Social activity symptoms

10–30

Nil

Can be converted to QALYs Useful for policy development Only measures function or symptom-based problems Does not address high levels of function

EuroQol

6 plus a visual analogue scale

Mobility Self-care Usual activity Pain/discomfort Anxiety/depression

1

Nil

Brief and simple to administer Has wide applicability Can be used to calculate QALYs Large ceiling effects likely in a sport and active recreation population

AQoL

15

Illness Independent living Social relationships Physical senses Psychological well-being

5

General injury population[101]

Increased sensitivity over the EuroQol and QWB Can be used to calculate QALYs Likely to have large ceiling effects Only measures low levels of function

SF-36

36

Physical function Role-physical Bodily pain Social functioning General health Vitality Role-emotional Mental health

5–10

Athletic injuries[6,75,102,103] Traumatic brain injury[104,105] Multi trauma + head injury[106] Orthopaedic injury[107,108]

Only generic measure with some validation in a sport and recreation population Does not measure change in sport and recreation Poor responsiveness for mental health subscale

SF-12

12

Physical function Role-physical Bodily pain Social functioning General health Vitality Role-emotional Mental health

2

General trauma[109]

Brief and simple to administer Omits items most relevant to a sport and active recreation population

SIP-136

136

Sleep/rest Emotional behaviour Body care and movement Household management Mobility

20–30

Rehabilitation patients[110] General trauma[20,21] Lower extremity trauma[111]

Comprehensive measure Has questions specific to active recreation Ceiling effects demonstrated Long completion time

Continued next page

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Outcome instrument

Measuring the Burden of Sports Injury


Table II. Summary of outcome measures

Outcome instrument

148


Table II. Contd No. of items

Domains

Time to complete (min)

Injury populations where it has been validated

Advantages and disadvantages

Social interaction Ambulation Alertness/behaviour Communication Recreation and pastimes Eating Work 68

Somatic autonomy Mobility control Communication and psychological autonomy Social interaction Emotional behaviour Mobility range

10–15

Head injury[105]

Reduced responder burden compared to the SIP-136 Omits many of the questions considered to be most relevant to a sport and active recreation population

FIM and FAM

18 (FIM) +12 additional (FAM)

Motor Cognitive Behavioural Communication Community functioning

FIM + FAM = 35

General trauma[112] Head injury[113,114]

Designed for use in inpatient rehabilitation programmes Only measures low levels of function Ceiling effects likely to be a problem

FCI

10

Excretory function Eating Sexual function Ambulation Hand/arm movement Bending/lifting Speech Auditory function Visual function

8

General trauma[21] Lower limb trauma[115]

Designed specifically for trauma patients Does not contain items specifically relevant to a sport and active recreation population Focuses on low levels of function

GOS and GOSE

7

Level of consciousness Independence in the home Independence outside the home Work Social and leisure activities Family and friends Return to normal life

15 min duration Does not cover domains outside leisure time

AQoL = Assessment of Quality of Life; FAM = Functional Assessment Measure; FCI = Functional Capacity Index; FIM = Functional Independence Measure; GLETQ = Godin LeisureTime Exercise Questionnaire; GOS = Glasgow Outcome Scale; GOSE = Glasgow Outcome Scale Extended; IPAQ = Short International Physical Activity Questionnaire; MFA = Musculoskeletal Function Assessment; PPAQ = Paffenbarger Physical Activity Questionnaire; QALYs = quality-adjusted life-years; QWB = Quality of Well-Being; SF-12 = 12-item Short Form Health Survey; SF-36 = Short Form-36 Health Survey; SIP-68 = the Sickness Impact Profile-68; SIP-136 = Sickness Impact Profile-136; SMFA = Short Musculoskeletal Function Assessment.

149

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Outcome instrument



Table II. Contd

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functions such as senses, sleep, emotions and pain. Environmental factors relating to medications, devices and treatment are addressed, as are activities and participation, but with a focus on low levels of functioning. The AQoL can also be used to calculate QALYs using the items contained in the last four domains (table II). The AQoL has been validated in an injury population.[101] However, its exclusion of activity and participation items and levels of function most relevant to a sport and active recreation population are likely to result in underestimation of the impact of injury in this group. This is reflected in a study in which 45% of a normal population reported scores in the highest decile.[127] A later version of the AQoL (AQoL Mark 2) has been extended to 20 items. High level mobility functions such as running are included and vitality is assessed. Community roles are addressed with sporting groups included in the examples. Though this version is better suited to a sport and active recreation or injury population, it has yet to be validated or used in these groups. 3.4 Short Form-36

The SF-36 has been widely used in sport and active recreation populations.[5,7,74-80] It contains 36 items over eight domains (table II) and provides a separate score for each subscale and mental component summary (MCS) and physical component summary (PCS) scores. Many of the items in the SF-36 are applicable to a sport and active recreation population, especially in the ICF domains of activities and participation relating to mobility, recreation and leisure and mental functions. The lack of cognitive and upper limb subscales could result in underestimation of the impact of injury in these areas. There is limited assessment of the psychometric properties of the SF-36 in sport and active recreation populations. A study of elite athletes found that serious injury was a predictor of lower PCS, MCS and subscale scores, and that mild injury was a predictor of lower PCS scores.[6] Another study on retired professional footballers found that those with clinical depression had lower MCS and PCS scores compared with those without depression.[75] ª 2010 Adis Data Information BV. All rights reserved.

These results, however, cannot readily be extrapolated to recreational athletes. Criterion validity was assessed in knee-injured sporting populations.[102,103] Good correlations (r = 0.57–0.72) were found between physical function measured by the SF-36 and knee function tests, with divergent validity demonstrated between the other subscales of the SF-36 and the knee function tests.[102,103] Ceiling effects were noted in the SF36 role physical subscale.[102] Good criterion validity was also demonstrated in general injury and traumatic brain injury (TBI) patients.[21,104,128] The reliability of the SF-36 demonstrated high variability between subscales (ICC = 0.04–0.77) in a sport and active recreation population with patella dislocation;[102] however, there was a median interval of 21 days between tests and factors particular to patella dislocation such as fluctuations of symptoms could have affected the results, as could the inclusion of children.[102] In TBI patients, good reliability was demonstrated across all subscales of the SF-36 for one study[104] and in less than half the subscales in another.[105] In sport and active recreation populations, improvements in the PCS and MCS have been demonstrated 2 years after surgery,[79] and changes in physical function, role function, bodily pain and social function subscales have been demonstrated as early as 5–6 weeks after injury.[5] High SRMs (0.5–1.1) were reported for the physical subscales but not the mental health subscales[128] in general injury patients. It is likely that the physical components of the SF-36 are more responsive than the mental components in this group. The SF-36 is suitable for use in a sport and active recreation population. Its main limitations are the potential for ceiling effects in some subscales and the lack of responsiveness of the mental health subscales. The suitability of the SF-36 for upper limb injuries requires further investigation, and further psychometric testing is required in sport and active recreation populations.[129] 3.5 Short Form-12

The SF-12 was derived by selecting 12 items that provided a >90% correlation with the SF-36 and covered each of the eight subscales. Selection Sports Med 2010; 40 (2)


was based on predictions from US population data and validated in chronic medical patients.[130] Though the SF-12 appears to be a valid alternative to the SF-36 in general, trauma and medical populations,[109,130] its omission of items relevant to sport and active recreation populations such as vigorous activities and walking long distances are likely to underestimate the impact of injury in this group. Therefore, the SF-36 would be preferable to the SF-12 in sport and active recreation populations. 3.6 Sickness Impact Profile-136

The SIP-136 has not been used in specific sport or active recreation studies; however, it has been used in studies of injuries commonly seen in sporting populations.[131,132] The SIP-136 assesses sickness-related behaviours and is designed to have broad applicability across a variety of illnesses and demographics. The SIP-136 contains 136 questions over 12 domains giving it increased content validity over shorter measures,[133] and contains a large number of concepts that can be linked to the ICF.[134] Those most relevant to a sport and active recreation population are related to energy, psychomotor function, exercise tolerance, muscle function and physical recreation.[135,136] The SIP136 can be scored to give physical, psychosocial well-being and individual category scores (table II). The psychometric properties of the SIP-136 have been established in a range of patients, including rehabilitation patients, but have not been assessed in a sport and active recreation population. One study, however, found that certain aspects of the SIP-136 had a much higher degree of relevance to sporting populations, especially those aspects relating to pain and recreational activities.[132] In trauma patients, good convergent validity (r > 0.60) was demonstrated between the PCS of the SIP-136 and the Functional Capacity Index (FCI),[21] and a moderate correlation (r = 0.41) was demonstrated between the SIP-136 and clinical measures of physical impairment.[111] A ceiling but not a floor effect was also demonstrated in trauma patients.[20] The SIP-136 was able to discriminate between treatment groups in conservatively managed ª 2010 Adis Data Information BV. All rights reserved.

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ankle sprains[131] and was responsive to changes that occurred after anterior cruciate ligament reconstruction at 3 and 12 months.[132] The SIP-136 was also sensitive to improvements in function in trauma patients with lower limb fractures over 6, 12 and 30 months.[91,111] The comprehensiveness of the SIP-136 and its inclusion of relevant subscales make it suitable for a sport and active recreation population. The main disadvantage of the SIP-136 is its long completion time, and further psychometric testing is required in a sport and active recreation population. 3.7 Sickness Impact Profile-68

The SIP-68 has been used in two studies involving general sport and active recreation populations[1,2] and has reliability, validity and responsiveness similar to that of the SIP-136 in rheumatology and medical patients.[137-139] The main disadvantage of the SIP-68 is that it omits many of the questions that are most relevant to a sport and active recreation population.[91,111,132] Fourteen of the 24 questions in the SIP-136 considered to be most relevant to a sport and active recreation population are omitted,[132] limiting the potential usefulness of this instrument in a sport and active recreation population. 4. Functional Outcome Measures Functional measures identified in our search and used in sport and active recreation populations were the Glasgow Outcome Scale (GOS)[85] and the Short Musculoskeletal Functional Assessment (SMFA).[86] Other suitable measures used in general injury studies include the Glasgow Outcome Scale Extended (GOSE),[140] Musculoskeletal Functional Assessment (MFA),[118,141-143] Functional Independence Measure (FIM) and Functional Assessment Measure (FAM),[112,113,144] and the FCI.[21,145,146] 4.1 The Functional Independence Measure and the Functional Assessment Measure

The FIM is an 18-item scale designed to measure change over the course of inpatient rehabilitation programmes and has motor and cognitive Sports Med 2010; 40 (2)

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components. The FAM consists of 12 additional items and was designed for use with the FIM. The questions focus on performance of activities relating to self-care and independence and do not contain items relevant to high levels of function. This is reflected in follow-up studies involving general trauma and TBI patients in which ceiling effects were reported for between 80% and 95% of subjects.[100,112-114] Therefore, the FIM and FAM are unlikely to measure outcomes meaningful to a sport and active recreation population. 4.2 The Functional Capacity Index (FCI)

The FCI was initially designed to predict 12-month outcomes for the injury descriptions contained in the abbreviated injury scale (AIS). The AIS is primarily a threat-to-life scale and does not accurately identify injuries that have high morbidity. The FCI was developed to rectify this.[147] The FCI questionnaire was later developed as an evaluative tool, utilizing these predictive weights in its scoring system.[21] The FCI has the advantage of being specifically designed for use in injury populations and has been validated in this group,[21] though further psychometric evaluation is required.[148] The FCI covers ten dimensions each with between three and seven categories of capacity that are weighted depending on their impact on everyday living[147] (table II). The FCI focuses on body functions with some dimensions such as ambulation and hand/arm movement also containing sub-categories relating to activities and participation and environmental factors. The FCI focuses on tasks necessary for everyday living and does not cover areas such as sport and active recreation.[21] As such, it is not suited to a sport and active recreation population. 4.3 Glasgow Outcome Scale and Glasgow Outcome Scale-Extended

The GOS was developed as a global measure of outcome following head injury, has been recommended for use in general injury studies,[149] and has been used in one study involving sport and active recreation participants.[85] The GOS is designed to reflect disability as defined by the ª 2010 Adis Data Information BV. All rights reserved.

WHO[150] and covers multiple aspects of the ICF relating mainly to activities and participation, across five domains.[116] The GOS is scored by allocating the patient to one of five broad categories ranging from dead to ‘‘resumption of normal activity despite minor deficits’’. The GOS contains a section on social and leisure activities but measures quantity, rather than quality, of participation.[150] This and the allowance of minor deficits in its highest category means that the impact of injury in a sport and active recreation population could be underestimated. Importantly, pre-injury status is considered when scoring the GOS. An extended version of the GOS was developed to increase sensitivity and reduce ceiling effects.[151,152] The upper three categories of good recovery, moderate disability and severe disability are subdivided to provide eight categories (table II). The GOSE has greater suitability over the GOS for sport and active recreation populations due to additional categories and allowing qualification of whether or not a patient has returned to ‘normal life’. Nevertheless, the GOSE has yet to be used in a sport and active recreation population. The psychometric properties of the GOSE have only been assessed in head injured populations. Its content validity is evidenced by good correlations with other functional measures (r = 0.46–0.89)[116,117,152] and the Beck depression inventory (r = 0.64) for all patients except the most severely disabled.[116] Modest associations were also demonstrated with various cognitive tests.[116,153] Administration by an interviewer using a structured interview is recommended for the GOSE to increase reliability.[150] Good intrarater reliability was found for face-to-face versus telephone interviews (Kw = 0.92).[154] Inter-rater reliability results were more variable. One study found low reliability (Kw = 0.56–0.57) both at discharge and 12 months after injury,[105] whereas other studies found acceptable levels (Kw = 0.84–0.98) through various modes of administration;[117,150,154] however, some studies were limited by small patient numbers.[154,155] Good reliability (Kw = 0.92) was also demonstrated for Sports Med 2010; 40 (2)


postal interviews.[155] Agreement on the GOSE was slightly better for those with severe injuries compared with those with minor injuries,[154] which could reduce its reliability in a sport and active recreation population. The GOSE was able to demonstrate change in a cohort of head-injured patients at 5–7 years after injury as compared with 12 months after injury.[117] Change was also demonstrated in a sample of TBI and general trauma patients at 3 and 6 months after injury,[151] and predicted increases in scores were also demonstrated over a 12-month period.[105] The categorical nature of the GOSE may reduce its sensitivity compared with continuous measures; however, this is yet to be established. Though predominantly used in TBI populations, the use of the GOSE in general trauma populations and its inclusion of relevant items suggests that it may be a suitable global measure of function for sport and active recreation populations. Further psychometric evaluation of the GOSE is required in this population, especially for minor injuries. Further evidence of reliability of the GOSE is needed. 4.4 Musculoskeletal Functional Assessment

The MFA is a self-reported measure developed to assess musculoskeletal disorders of the extremities, including fractures and soft tissue injuries, making the MFA particularly relevant to sport and active recreation populations.[1,2,156] The MFA includes 101 items over ten categories. The MFA contains many ICF sub-categories relevant to a sport and active recreation population. Activities and participation, and to a lesser extent body functions and body structures, are covered and include items such as running, changes in physical recreation activities and changes in physical fitness due to disability[157] (table II). Scoring allows for a total score as well as category sub-scores.[20] Despite use in injury studies,[118,141-143] the MFA has not been used in sport and active recreation injury studies. Validity of the MFA has been established in trauma patients.[20,118] Good correlations have been demonstrated between physician ratings of extremity function and MFA extremity function ª 2010 Adis Data Information BV. All rights reserved.

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(r = 0.40–0.66), but not between other subscores.[20,118] Convergent validity was demonstrated between various clinical measures and the relevant lower extremity and upper extremity MFA items, and between self-ratings of health and changes in activity.[20,118] Construct validity relating to injury and demographic characteristics and predicted MFA scores were also demonstrated.[118] The total score of the MFA does not have floor or ceiling effects,[20,157] though ceiling effects were noted within individual categories.[20] The MFA has demonstrated good reliability (ICC = 0.70–0.92) for self-administration and inter-rater reliability, with the MFA more reliable in injury than in arthritis groups.[20,157] Good responsiveness (SRM = 0.74) has been demonstrated over a 6-month period for the overall MFA score, but was variable between categories with the categories of family relationships and mobility showing the lowest levels of responsiveness.[20] The MFA could be an appropriate outcome measure for musculoskeletal sport and active recreation injuries. The ability of the MFA to accurately assess function in non-musculoskeletal sport and active recreation injuries is unknown; however, the inclusion of a cognitive component and general function questions suggest that it is likely to be acceptable for broader injury groups. Psychometric analysis of the MFA in a sport and active recreation population is needed. 4.5 The Short Musculoskeletal Functional Assessment

The SMFA was developed to reduce respondent burden for the MFA whilst maintaining important items. It has been used in one sport and active recreation study.[86] Though the SMFA has been shown to be reliable, valid and responsive in patients with extremity disorders,[119] the questionnaire does not include many of the MFA items most relevant to a sport and active recreation context such as those related to running and the category relating to leisure and recreational activities. As such, the SMFA is likely to be a less appropriate measure Sports Med 2010; 40 (2)

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of function than the MFA in a sport and active recreation context.

5. Physical Activity Measures 5.1 The Short International Physical Activity Questionnaire

The short International Physical Activity Questionnaire (IPAQ) measures physical activity over the previous 7 days or a typical week over four domains (table II). Time spent in highintensity, medium-intensity and walking activities and sitting is recorded and MET scores are obtained for each category where 1 MET is the resting metabolic rate during quiet sitting. A total score is derived as well as separate scores for each category except sitting. The questionnaire was designed for physical activity surveillance across a variety of cultures in response to the need for a standardized physical activity measure. The short IPAQ has been validated in general populations across a number of countries. Validity has been assessed against accelerometers or motion detecting devices with only fair agreement (p = 0.30–0.39);[158-160] however, this may be due to accelerometers not measuring all aspects of physical activity and consequently underestimating physical activity in some people.[161] Good convergent validity (r ‡ 0.5) was demonstrated between the IPAQ and other physical activity questionnaires and physical activity logs.[160,162,163] Though not validated in injury populations, one study showed that patients with greater severity of osteoarthritis of the knee and hip had lower activity levels as measured by the short IPAQ.[120] A similar relationship may exist between disability due to injury and the short IPAQ. A large international study found good test-retest reliability (p = 0.74) for telephone-administered and self-administered questionnaires,[158] with lower reliability in rural and undeveloped areas. Another study found moderate reliability (ICC = 0.68);[164] however, two European studies found low reliability (ICC = 0.45–0.54).[160,165] Physical activity can vary from week to week, hence differences may be partly related to different administration periods as ª 2010 Adis Data Information BV. All rights reserved.

studies with longer re-administration periods reported lower reliability.[160,165] The short IPAQ has the advantage of measuring physical activity across a number of domains and is suitable for use in a variety of cultures. The responsiveness of the short IPAQ in an injury context is unknown and consequently the developers do not recommend its use in smallscale intervention studies.[166] The variability of the results obtained from reliability studies suggests that further evaluation is required. 5.2 Paffenbarger Physical Activity Questionnaire

The Paffenbarger Physical Activity Questionnaire (PPAQ) or College Alumnus physical activity questionnaire was developed for use in exercise and chronic disease epidemiology studies. The PPAQ measures calories expended in sport, leisure and recreational activities, as well as flights of stairs climbed and city blocks walked. Sport and recreation activities are listed as weeks in the past year that each activity was performed, whereas other areas are recorded for the previous week (table II). This allows for variation in sporting participation habits but in the context of injury will limit the time frames for which it can be used. The PPAQ does not measure physical activity across multiple domains; however, it does allow time spent in each sport or recreation activity to be listed separately.[167] Validity and reliability studies have involved general adult populations and university students. Only fair agreement was demonstrated between the PPAQ and accelerometer readings (r = 0.29–0.30)[168,169] and activity logs that measured total activity (r = 0.31).[168] However, when only the activity log items included in the PPAQ were compared, a high level of correlation was found (r = 0.60).[169] Another study found good agreement (r > 0.50) between the PPAQ and five of seven other physical activity questionnaires.[170] Two studies found good test-retest reliability when administered within a time frame of 1 month,[168,169] whereas a study that used a time frame of 7–12 weeks found poor test-retest reliability (r = 0.58). When the reliability results Sports Med 2010; 40 (2)


were recalculated using only participants who reported no change in their activity levels, the correlation increased significantly (r = 0.69).[171] The PPAQ appears to be valid and reliable in populations with similar demographics to a sport and active recreation population; however, the use of selected domains and activities means that some aspects of physical activity such as cycling to and from work or work-based activities may be missed. The 12-month time frame for recording sport and recreation activities is only appropriate for measuring recovery over very long periods. Nevertheless, the scoring system could be modified to cover activities over the last month or week. 5.3 Godin Leisure-Time Exercise Questionnaire

The Godin Leisure-Time Exercise Questionnaire (GLETQ) is a four-item questionnaire used to assess the number of times in an average week participants spend in strenuous, moderate and mild physical activity for more than 15 minutes[172] (table II). A score is obtained that can be converted to METs. Though not used specifically as an outcome measure, the GLETQ has been used to measure physical activity in patients with existing lower limb and spinal cord injuries.[173,174] The GLETQ has undergone minimal psychometric testing. Accelerometer correlations were fair (r = 0.32–0.35).[168,175] Correlations between the GLETQ and a 4-week activity diary were lower than the other questionnaires (r = 0.36).[168] High test-retest reliability was reported (r = 0.75–0.82) when administered within a 2-week period.[175,176] The GLETQ has demonstrated changes in activity levels across phases of treatment and recovery in breast cancer patients[177] and could show changes in activity associated with injury and its phases of recovery. The GLETQ measures aspects of physical activity relevant to a sport and active recreation population but it does not account for physical activity across other domains. The GLETQ measures exercise episodes per week greater than 15 minutes rather than actual time spent and thus may underestimate overall activity levels. The reliability of the GLETQ is good and its brevity is ª 2010 Adis Data Information BV. All rights reserved.

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a desirable trait for a sport and active recreation population. 6. Conclusion Despite the plethora of outcome measures available, none have been specifically designed to measure injury outcomes in a general sport and active recreation population. In the absence of a purpose-designed instrument, there are existing generic measures that could, alone or in combination with others, be useful for measuring outcomes in this group. The SF-36 covers many of the areas of HR-QOL relevant to a sport and active recreation population and enables comparison with other disease and injury populations. Where a detailed measure of function is required, the MFA could be useful, while the GOSE may have merit as a global measure of function. Physical activity measures present a standardized method for measuring return to activity in sport and active recreation populations with the short IPAQ appearing to be the most comprehensive of this group. Ultimately, the choice of outcome measure will depend on the requirements of the users. So far there is no core set for sport and active recreation injury patients and though the ICF can provide a general framework in which to assess the appropriateness of existing measures, the development of a core set would assist researchers and clinicians in selecting the combination of outcome measures that would provide the most comprehensive assessment of disability and recovery in this group. Future research should focus on validating existing generic measures suitable for sport and active recreation populations as well as developing a measure specific to their requirements based on an ICF core set. Only through improved measurement of outcomes will gains be made in quantifying the burden of sport and active recreation injury outcomes. Acknowledgements Dr Belinda Gabbe was supported by a Career Development Award from the National Health and Medical Research

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Council of Australia during the preparation of this review. The authors have no conflicts of interest that are directly relevant to the content of this review.

19. 20.

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167. Paffenbarger R, Hyde R, Wing A, et al. Physical activity, all-cause mortality, and longevity of college alumni. New Engl J Med 1986; 314 (10): 605-13 168. Jacobs D, Ainsworth B, Hartman T, et al. A simultaneous evaluation of 10 commonly used physical activity questionnaires. Med Sci Sports Exerc 1993; 25 (1): 81-91 169. Ainsworth B, Leon A, Richardson M, et al. Accuracy of the College Alumnus Physical Activity Questionnaire. J Clin Epidemiol 1993; 46 (12): 1403-11 170. Albanes D, Conway J, Taylor P, et al. Validation and comparison of eight physical activity questionnaires. Epidemiology 1990; 1 (1): 65-71 171. Washburn R, Smith K, Goldfield S, et al. Reliability and physiologic correlates of the Harvard Alumni Activity Survey in a general population. J Clin Epidemiol 1991; 44 (12): 1319-26 172. Godin G, Shephard R. A simple method to assess exercise behaviour in the community. Can J Appl Sports Sci 1985; 10 (3): 141-6 173. Godin G, Colantonio A, Davis G, et al. Prediction of leisure time exercise behavior among a group of lower-limb disabled adults. J Clin Psychol 1986; 42 (2): 272-9


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Correspondence: Dr Belinda J. Gabbe, Department of Epidemiology and Preventive Medicine, Monash University, Alfred Hospital, Commercial Rd, Melbourne, VIC 3004, Australia. E-mail: [email protected]

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Sports Med 2010; 40 (2): 163-178 0112-1642/10/0002-0163/$49.95/0

RESEARCH REVIEW


Match and Training Injuries in Rugby League A Review of Published Studies Doug A. King,1,2 Patria A. Hume,2 Peter D. Milburn3 and Dain Guttenbeil4 1 Emergency Department, Hutt Valley District Health Board, Lower Hutt, New Zealand 2 Sports Performance Research Institute New Zealand, School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand 3 School of Physiotherapy and Exercise Science, Gold Coast Campus Griffith University, Gold Coast, Queensland, Australia 4 New Zealand Rugby League Inc., Penrose, Auckland, New Zealand

Abstract

Rugby league is an international collision sport played by junior, amateur, semiprofessional and professional players. The game requires participants to be involved in physically demanding activities such as running, tackling, passing and sprinting, and musculoskeletal injuries are common. A review of injuries in junior and senior rugby league players published in Sports Medicine in 2004 reported that injuries to the head and neck and muscular injuries were common in senior rugby league players, while fractures and injuries to the knee were common in junior players. This current review updates the descriptive data on rugby league epidemiology and adds information for semiprofessional, amateur and junior levels of participation in both match and training environments using studies identified through searches of PubMed, CINHAL, Ovid, MEDLINE, SCOPUS and SportDiscus databases. This review also discusses the issues surrounding the definitions of injury exposure, injury rate, injury severity and classification of injury site and type for rugby league injuries. Studies on the incidence of injuries in rugby league have suffered from inconsistencies in the injury definitions utilized. Some studies on rugby league injuries have utilized a criterion of a missed match as an injury definition, total injury incidences or a combination of both timeloss and non-time-loss injuries, while other studies have incorporated a medical treatment injury definition. Efforts to establish a standard definition for rugby league injuries have been difficult, especially as some researchers were not in favour of a definition that was all-encompassing and enabled non-time-loss injuries to be recorded. A definition of rugby league injury has been suggested based on agreement by a group of international researchers. The majority of injuries occur in the match environment, with rates typically increasing as the playing level increases. However, professional level injury rates were reportedly less than semiprofessional participation. Only a few studies have reported training injuries in rugby league, where injury rates were reported to be less than match injuries. Approximately 16–30% of all

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rugby league injuries have been reported as severe, which places demands upon other team members and, if the player returns to playing too early, places them at an increased risk of further injuries. Early research in rugby league identified that ligament and joint injuries were the common injuries, occurring primarily to the knee. More recently, studies have shown a change in anatomical injury sites at all levels of participation. Although the lower limb was the frequent injury region reported previously, the shoulder has now been reported to be the most common injury site. Changes in injury site and type could be used to prompt further research and development of injury reduction programmes to readdress the issue of injuries that occur as a result of participation in rugby league activities. Further research is warranted at all participation levels of rugby league in both the match and training environments to confirm the strongest risk factors for injury.

Rugby league is a team contact sport played internationally. It consists of 13 players in each team, and is typically (but not always) played under a limited interchange rule where up to 12 interchanges of players are permitted in matches. Each team is permitted six tackles in possession of the ball with which they must advance into the opposition’s territory and score a try.[1-3] The ball must only be passed backwards but can be carried or kicked into the opposition’s territory.[1,3] At the completion of six tackles the ball is immediately given to the opposition team to commence their set of six tackles.[1,2] Most teams often kick the ball after the fifth tackle (ceding the possession to the opposition) to avoid being tackled a sixth time, in an attempt to gain further territorial advantage. The same players are therefore involved in both attack and defence. As with all sport, there is a risk of sustaining an injury when participating in rugby league activities. The game is intermittent in nature, requiring participants to compete in a challenging physical contest. Players often undergo frequent bouts of high-intensity activity (e.g. tackling, sprinting, running and passing) interspersed with short bouts of low-intensity activity (e.g. jogging, walking and standing).[4-7] As a result of the intermittent and contact nature of the game, the physiological demands of rugby league are complex. Players are required to have maximal aerobic power, speed, muscular strength, and power and agility appropriately developed to be able to compete in the match environment.[4-7] As a ª 2010 Adis Data Information BV. All rights reserved.

result of the physical and intense nature of the game, musculoskeletal injuries are common.[1,7,8] The rugby league team consists of two main groups of participants (forwards and backs) on the field and reserves available for interchange.[9-11] The demands on the participants vary according to the specific positions played,[9-11] with forwards (two props, one hooker, two second rowers and one lock) more predominately involved in large numbers of physical collisions and tackles.[12] Backs (one half-back, one stand-off/five-eighth, two centres, two wings and one fullback) spend more time in free running but are also involved in tackles and collisions.[7,10-12] The aim of this study was to review and update the descriptive data on rugby league injury epidemiology and add information for semiprofessional, amateur and junior levels of participation in both match and training environments. 1. Methods Searches of PubMed, CINHAL, Ovid, MEDLINE, SCOPUS, and SportDiscus databases were performed to identify studies published in English prior to October 2008. The computer databases provided access to sports-oriented and biomedical journals, serial publications, books, theses, conference papers and related research published since 1948. Terms utilized for the search of relevant research studies included ‘rugby league’ and ‘injury incidence’. Qualifying studies were mainly uncontrolled trials and the outcome Sports Med 2010; 40 (2)

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variables were injury incidence, injury site, injury type, match time, seasonal variations and injury severity of rugby league players. 2. Findings Thirty-five published studies, mainly conducted in Australia and New Zealand, have reported the injury incidence of rugby league participants in matches (i.e. tournaments and competitions) and/or training (table I). Tournaments differ from matches in two main areas: (i) tournament matches can vary in the periods between matches (i.e. several matches in one day through to one

game a week); and (ii) they can comprise players of different participation levels either playing against each other or competing in the same team. Conversely, matches are typically undertaken on a regular schedule over a longer period for a specific participation level. Injury incidence has changed with changes to the rules of the game, and with the resulting changes to the activity and intensity at which the game is played. Although there have been World Cup tournaments for both male and female participants, there have been no published studies on the injury incidence in these competitions, and several levels of competition do not include females (table I).

Table I. Prospective rugby league epidemiological publications analysed by type of playing population for matches and training by country of origin Playing population level

Sex

Studies conducted on match injuries

Studies conducted on training injuries

Professional tournament

Male

None

None

Professional match

Male Male

England[13-21] Australia[2,22-24]

None None

Semiprofessional tournaments

None

None

None

Semiprofessional teams

Male Male

Australia[8,25] New Zealand[26]

Australia[8,27,28] Australia[8,27,28]

Sub-elite tournament

Male

None

None

Sub-elite teams

Male

Australia[29]

Australia[30,31]

Amateur tournament

Male Female

None New Zealand[32]

None None

Amateur teams

Male Male

Australia[33] New Zealand[34,35]

New Zealand[36] New Zealand[36]

Masters tournament

Male

None

None

Masters teams

Male

None

None

School-level tournaments

Male Female

None None

None None

School-level team

Male Female

None None

None None

School-level tournaments

Male Female

None None

None None

Junior

Male Male Female

Australia[37,38] New Zealand[39] None

None None None

Sevens

Male Male

Australia[40] New Zealand[41]

None None

Competition

Male Male

New Zealand[42] New Zealand[42]

None None

Review of injuries at various levels

Male Male Male Female

New Zealand[34] Australia[12,43] England[3] None

None None None None


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Worldwide, the majority of rugby league participants are amateur (i.e. they derive income from another source), therefore the majority of injuries that occur from rugby league participation are incurred by these participants, but the rate of injury differs for professional players. Although there have been many studies reporting both match and training injures in rugby league and conducted at various levels of participation, there are some participation levels, such as masters and school level, where no prospective injury epidemiological studies have been completed. There was also a paucity of studies on amateur and junior levels of participation. While there is an assumption that the results of epidemiological studies on professional participants translate to other cohorts of participants in other countries, these assumptions have yet to be tested.[44] 3. Injury Definitions for Rugby League A fundamental process, and typically the first step for the injury prevention process, is ongoing injury surveillance.[45-48] However, comparison of results from injury surveillance studies is often difficult due to the inconsistencies in the injury definitions utilized[46,47] and the methodologies undertaken,[45,46,49-51] and therefore the results and conclusions obtained can often have important differences.[1,12,13,23,45,46,50,51] To fully understand the extent and nature of rugby league injuries, it is necessary to consider the various injury definitions that have been used for collating and assessing rugby league injuries. The definition of a sports injury is frequently discussed and, to date, there is no universally accepted definition of a sports injury.[49,52-54] Sports injury definitions are typically provided as operational criteria for the recording and reporting of injuries rather than as a theoretical definition.[55] These definitions are usually broadly based around the concept that ‘‘bodily damage caused by a transfer or absence of energy’’ is what causes injuries to occur.[55] This concept is useful in clarifying whether an incident in rugby league should be recorded as an injury. Several team sports (cricket,[47] football/soccer[56] and rugby union[55]) have published consensus statements in ª 2010 Adis Data Information BV. All rights reserved.

an attempt to obtain more consistent and comparable results from studies undertaken in these sporting activities. Studies on the incidence of injuries in rugby league are no different and have suffered from inconsistencies in the injury definitions utilized (tables II–IV).[43,51] Variations reported for injury incidence are often the result of data obtained from relatively small numbers of players and teams,[3,14] and often over a limited time frame.[43] Some studies on rugby league injuries (as shown in tables II–IV) have utilized criteria of a missed match as an injury definition,[2,3,9,21,29,38,58-60] total injury incidences[8,13,15,22,26-28,31-33,35-37,39-42,57,61] or a combination of both time-loss and non-timeloss injuries,[8,13,22,26-28,32,35,39,41,52,57,61,62] while other studies have incorporated a medical treatment injury definition.[22,24] Consequently, the definition of an injury in rugby league has been widely discussed and disputed[52-54] and to date there is no uniformly accepted definition. The key issue in establishing the injury definition has been centred on which injuries should actually be recorded. Studies have reported that up to 90% of sports injuries have been recorded as non-time-loss injuries.[63] This has been similar in some studies in rugby league where non-time-loss injuries have been reported to be between 85%[57] and 93%[28] of match injuries, and up to 98%[28] of training injuries. The inclusion of non-time-loss injuries has been reported to bias the reported data towards non-time-loss injuries and, as a result of this bias, head and neck injuries make up a large proportion of the total injuries in rugby league.[43] The use of a time-loss definition directs attention to those injuries that are most likely to have direct consequences on players, their team and their club performance;[64] however, the use of this definition understates the effects that non-timeloss injuries have on the healthcare system.[14] The time-loss definition also contains certain inaccuracies, such as an amateur player who trains only twice a week has a greater likelihood of recovering from an injury before the next training session than a subelite or elite level player who trains daily.[65] An injured player may also participate in a training session but the participation Sports Med 2010; 40 (2)


167

Table II. Professional rugby league injury definitions used and the resulting average injury rate and rates for matches and training Study

Level of participation

Total injury rate

Missed match/ training injury rate

Injury definition used

Seward et al.[22]

Professional (8 teams, 3 grades, 1 year)

139 per 1000 player hours


Injury that caused a player to be unavailable for selection in a match, or participation in a training session or any other injury that required specific medical treatment, other than routine conservative measures

Gibbs[2]

Professional (1 club, 3 grades over 3 years)

–

45 per 1000 player game hours

That occurring during a game that caused a player to miss a subsequent match

Estell et al.[57]

Professional (2 grades) and elite junior (4 teams) over 1 season



Pain, discomfort or disability arising during or immediately after, and as a result of, playing in a rugby league match

Stephenson et al.[15]

Professional (1 club, 2 grades over 4 seasons)

114 per 1000 hours of match play

HodgsonPhillips et al.[13]

Professional (1 team over 4 seasons)



Pain, discomfort, disability or illness (new or recurrent) that the player acknowledged after participating in a rugby league-related activity/game

Gissane et al.[3]

Professional (pooled data from 4 prospective studies: Seward et al.,[22] Gibbs,[2] Stephenson et al.,[15] Gissane et al.[17])

–


Injury requiring a player to miss the subsequent game

Gissane et al.[21]

Professional (1 club, 9 seasons)

–


A physical impairment received during a competitive match that prevented a player from being available for selection to play in the next game

Orchard[58]

Professional (1 club, 2 grades over 6 seasons)

–


Injury requiring a player to miss a subsequent game

O’Connor[59]

Professional (100 players from 13 clubs)

–


An injury was recorded if there was: (a) pain and tenderness in the adductors or at the adductor bonetendon junction; (b) pain and weakness on resisted adduction; and (c) the player was unable to complete training or a game and missed the next training session

Orchard et al.[24]

Professional State of Origin from 2000 to 2006 (1 team, 3 games a year)



A match injury recurrence (for the State of Origin team) was defined as an injury to the same body part that had been medically assessed prior to the start of the match and which caused the player to miss subsequent games for his club after the Origin match

The onset of pain or a disability that occurred while playing rugby league football

– indicates no data available.

level may be restricted by the injury or they may be undergoing a modified training session.[65] Recent attempts by researchers to establish a standard definition for rugby league injuries have been difficult,[52,53] especially as some researchers were not in favour of a definition that was allencompassing and enabled non-time-loss injuries to be recorded. The following definition of rugby league injury was eventually agreed to by all ª 2010 Adis Data Information BV. All rights reserved.

but two of the six researchers, and is therefore suggested for use in forthcoming studies: ‘‘Any pain or disability that occurs during participation in a rugby league match or training activities that is sustained by a player, irrespective of the need for match or training time loss or for first aid or medical attention. An injury that results in a player requiring first aid or medical attention is referred to as a ‘medical attention injury’ and an Sports Med 2010; 40 (2)

King et al.

168

Table III. Semiprofessional rugby league injury definitions used and the resulting average injury rate and rates for matches and training Study


Total injury incidence

Missed match/training injury incidence


Gabbett[27]

Semiprofessional (60 players over 1 season)

27 per 1000 training hours


Any pain or disability suffered by a player that was subsequently assessed by the head trainer during a training session or immediately after the training session

Gabbett[8]

Semiprofessional (156 players over 2 seasons)

825 per 1000 playing hours; 45 per 1000 training hours

68 per 1000 playing hours; 1 per 1000 training hours

Any pain or disability suffered by a player during a match or training session, and subsequently assess by the head trainer during or immediately following the match or training session

Gabbett[31]

Sub-elite (220 players, 3 years)

78 – 157 per 1000 training hours

19–33 per 1000 training hours

Any pain or disability suffered by a player that was subsequently assessed by the head trainer during, or immediately following the training session

Gabbett[28]

Semiprofessional (79 players, 1 year)

106 per 1000 training hours; 917 per 1000 playing hours

2 per 1000 training hours; 65 per 1000 playing hours

Any pain or disability suffered by a player during a match or training session, and subsequently assessed by the head trainer during or immediately after the match or training session

Gabbett[9]

Semiprofessional (156 players, 2 seasons)

–

68 per 1000 playing hours

Any pain or disability suffered by a player during a match that resulted in the player missing a subsequent match

Gabbett[29]

Sub-elite (1 sub-elite club over three competitive seasons [a = unlimited interchange, b = limited interchange])

–

(a) 73 per 1000 playing hours; (b) 51 per 1000 playing hours

Any pain, disability or injury that occurred as a result of a competition game that caused the player to miss a subsequent game

Gabbett et al.[60]

Semiprofessional (1 club, 153 players over 4 years)

–


Any pain, disability or injury that occurred as a result of a competition match that caused a player to miss a subsequent match

King et al.[26]

Semiprofessional (8 teams, 240 players, 1 year)



Any pain or disability suffered by a player during a match that required advice and/or treatment


injury that results in the player being unable to partake in full part of future training and/or match activities is referred to as a ‘time loss’ injury.’’ [52] An advantage of the all-encompassing injury definition enables comparison between rugby union[55] and soccer,[56] as the injury definitions are similar. The disadvantage is that there are possibly more transient/non-missed match injuries recorded in rugby league and compliance with a broad injury definition may be limited. This was addressed with the recommendation that both total injuries (all injuries recorded) and injuries that result in time loss/missed match/ training be reported, enabling inter-study comparisons to be undertaken in future research. For further information on the debate regarding ª 2010 Adis Data Information BV. All rights reserved.

definitions of injury please see Orchard and Hoskins[54] and Hodgson et al.[53] 3.1 Definition of Injury Exposure and Injury Rate for Rugby League

There is no set format for data collection for sports participation, although the reporting of injury incidence in sports is becoming more standardized, enabling comparison of results between sporting codes[66] and different environments (e.g. training, appearances and competition). Studies involving all levels of rugby league participation[1,12] have reported injury rates (tables II–IV) using both a denominator (number of athletes, games, appearances) and a numerator Sports Med 2010; 40 (2)


169

(exposure measure),[67,68] expressed, for example, as injury rate per 1000 playing hours. To calculate the injury risk exposure hours for a rugby league team, the number of players (13; NP) on the field at any time is multiplied by the game duration (80 minutes, or £1.33 hours at different participation levels; GD). The result is 17.3 player exposure hours per team per game. Game injury risk exposure hours for the team are calculated by multiplying the player exposure hours per team per game by the number of games

(NG); e.g. 23 games per season gives 13NP · 1.3GD · 23NG = 398 game injury risk exposure hours.[8,12,27,28,33,40,62,67-70] 3.2 Definition of Injury Severity for Rugby League

Assessment of sports injury severity is another aspect that has also not achieved consensus in the literature. A recommendation for classification of injury severity has been proposed that relates

Table IV. Amateur rugby league injury definitions used and the resulting average injury rate and rates for matches and training Study


Total injury incidence

Missed match/training injury incidence


Norton et al.[42]

Amateur (24 teams over 1 season)

25 per 1000 hours of play; 0.03 per 1000 hours of training

–

Injury occurring during a match or training, for which medical attention was sought, or the player was unable to attend or take part in training or a match

Pringle et al.[61]

Amateur (1730 players age 6–15 y over 1 season)



A minor injury was defined as one where the player was still in discomfort immediately after the game, but was able to play the following week. A moderate injury was defined as one that prevented the player from participating in the following week’s game

Raftery et al.[37]

Amateur (253 junior teams over 1 year)


–

Any incident that required medical or paramedical review, missed participation at one training session or non-participation in one game

Gabbett[33]

Amateur (9 teams over 3 seasons)

161 per 1000 game hours

–

Injury that was subsequently assessed by the head trainer during or immediately after the match

Gabbett[40]

Amateur (168 players, 3 rugby league sevens tournaments)


–

Any pain or disability suffered by a player that was subsequently assessed by the head trainer during or immediately after a rugby league sevens match

King et al.[41]

Rugby league sevens (semiprofessional and amateur)



Any pain or disability experienced by a player during a match that required advice and/or treatment

King[39]

Junior (3 teams in under 16 and 1 team in under 18 competition)




King et al.[35]

Amateur (1 team 50 players, 1 year)



Any physical or medical condition that occurred during participation in a rugby league match that required medical treatment or resulted in missed match participation

King et al.[32]

Amateur women’s tournament (5 teams over 3 days)




King et al.[36]

Amateur training (1 team, 50 players, 1 year)



Any physical or medical condition that occurred during participation in rugby league training activities that required medical treatment or resulted in missed training participation

Gabbett[38]

Junior rugby league (80 players over four competitive seasons)

–


Any pain or disability experienced by a player during a match that resulted in the player missing a subsequent match



Sports Med 2010; 40 (2)

King et al.

170

Table V. Injury severity classifications for rugby league Study

Injury severity non-missed participation

minor

moderate

major

King et al.[26,36,41]

Transient (0 games/training missed)

1 game/training week missed

2–4 games/training weeks missed

‡5 games/training weeks missed

Hodgson-Phillips et al.[14]

Transient (0 games missed)

1 game missed

2–4 games missed

‡5 games weeks missed

King[39]





Gabbett[8,12,27,33,38,40]





Self-care by participant

Healthcare professional

Assessed at a hospital ‡5 games or weeks missed

Stevenson et al.[72] Hodgson-Phillips et al.[13]


Sandelin et al.[73] Gibbs[2]


1 game missed

2–4 games missed

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