Musculoskeletal Disorders in Health-Related Occupations (Biomedical and Health Research, 49)

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MUSCULOSKELETAL DISORDERS IN HEALTH-RELATED OCCUPATIONS

Biomedical and Health Research Volume 49 Earlier published in this series Vol. 14. G. ter Heege (Ed.), EURO-QUAL Vol. 15. N. Katunuma, H. Kido, H. Fritz and J. Travis (Eds.), Medical Aspects of Proteases and Protease Inhibitors Vol. 16. P.I. Haris and D. Chapman (Eds.), New Biomedical Materials Vol. 17. J.J.F. Schroots, R. Fernandez-Ballesteros and G. Rudinger (Eds.), Aging in Europe Vol. 18. R. Leidl (Ed.), Health Care and its Financing in the Single European Market Vol. 19. P. Jenner and R. Demirdamar (Eds.), Dopamine Receptor Subtypes Vol. 20. P.I. Haris and D. Chapman (Eds.), Biomembrane Structures Vol. 21. N. Yoganandan, F.A. Pintar, S.J. Larson and A. Sances Jr. (Eds.), Frontiers in Head and Neck Trauma Vol. 22. J. Matsoukas and T. Mavromoustakos (Eds.), Bioactive Peptides in Drug Discovery and Design: Medical Aspects Vol. 23. M. Hallen (Ed.), Human Genome Analysis Vol. 24. S.S. Baig (Ed.), Cancer Research Supported under BIOMED 1 Vol. 25. N.J. Gooderham (Ed.), Drug Metabolism: Towards the Next Millennium Vol. 26. P. Jenner (Ed.), A Molecular Biology Approach to Parkinson's Disease Vol. 27. P.A. Frey and D.B. Northrop (Eds.), Enzymatic Mechanisms Vol. 28. A.M.N. Gardner and R.H. Fox, The Venous System in Health and Disease Vol. 29. G. Pawelec (Ed.), EUCAMBIS: Immunology and Ageing in Europe Vol. 30. J.F. Stoltz, M. Singh and P. Riha, Hemorheology in Practice Vol. 31. B.J. Njio, A. Stenvik, R.S. Ireland and B. Prahl-Andersen (Eds.), EURO-QUAL Vol. 32. B.J. Njio, B. Prahl-Andersen, G. ter Heege, A. Stenvik and R.S. Ireland (Eds.), Quality of Orthodontic Care Vol. 33. H.H. Goebel, S.E. Mole and B.D. Lake (Eds.), The Neuronal Ceroid Lipofuscinoses (Batten Disease) Vol. 34. G.J. Bellingan and G.J. Laurent (Eds.), Acute Lung Injury: From Inflammation to Repair Vol. 35. M. Schlaud (Ed.), Comparison and Harmonisation of Denominator Data for Primary Health Care Research in Countries of the European Community Vol. 36. F.F. Parl, Estrogens, Estrogen Receptor and Breast Cancer Vol. 37. J.M. Ntambi (Ed.), Adipocyte Biology and Hormone Signaling Vol. 38. N. Yoganandan and F.A. Pintar (Eds.), Frontiers in Whiplash Trauma Vol. 39. J.-M. Graf von der Schulenburg (Ed.), The Influence of Economic Evaluation Studies on Health Care Decision-Making Vol. 40. H. Leino-Kilpi, M. Valimaki, M. Arndt, T. Dassen, M. Gasull, C. Lemonidou, P.A. Scott, G. Bansemir, E. Cabrera, H. Papaevangelou and J. Me Parland, Patient's Autonomy, Privacy and Informed Consent Vol. 41. T.M. Gress (Ed.), Molecular Pathogenesis of Pancreatic Cancer Vol. 42. J.-F. Stoltz (Ed.), Mechanobiology: Cartilage and Chondrocyte Vol. 43. B. Shaw, G. Semb, P. Nelson, V. Brattstrom, K. M01sted and B. Prahl-Andersen, The Eurocleft Proje 1996-2000 Vol. 44. R. Coppo and L. Peruzzi (Eds.), Moderately Proteinuric IgA Nephropathy in the Young Vol. 45. L. Turski, D.D. Schoepp and E.A. Cavalheiro (Eds.), Excitatory Amino Acids: Ten Years Later Vol. 46.1. Philp (Ed.), Family Care of Older People in Europe Vol. 47. H. Aldskogius and J. Fraher (Eds.), Glial Interfaces in the Nervous System Vol. 48. H. ten Have and R. Janssens (Eds.), Palliative Care in Europe

ISSN: 0929-6743

Musculoskeletal Disorders in Health-Related Occupations Edited by Thomas Reilly Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom

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Preface Musculoskeletal disease constitutes an enormous problem for contemporary workforces. Back problems in particular have been targeted as a major focus for research. The economic benefits of reducing musculoskeletal complaints are well recognised but the emphasis on quantitative costing has been in terms of treatment rather than prevention. Since musculoskeletal disease may be insidious in its emergence rather than linked directly with a single event, the link with working practices is not easily proven. Lifting and manual handling activities have been associated with musculoskeletal complaints, due to excessive acute loading or repetitive loading on the human. A hallmark of an ergonomics approach towards improving safety in the working environment is the design of a better fit between the demands of the job and the capabilities of the individual worker to meet these demands. This book owes its origin to the Biomed IV project, a collaborative research programme funded by the European Commission (Contract BmH4-CT96-1057) Liverpool John Moores University, Free University of Amsterdam, Vrije Universiteit Brussel. The partners were three Universities steeped in a tradition of ergonomics work. The research programme was focused on musculoskeletal disorders in healthrelated occupations. It is ironical that among health carers there is a concern that working practices themselves can be a source of damage to the health of the worker. The fifteen chapters in this book offer a glimpse into the problems of musculoskeletal disorders and the means of their investigation. Ergonomics entails multidisciplinary research and this approach permeates the contents. The background to the research programme as a whole is presented at the outset and the research is rounded off in the final chapter. In between are reviews of more fundamental work so that the methodologies used may be appreciated. Their applications are illustrated where appropriate with observations from the Biomed IV project. A comprehensive set of reviews is provided, in particular for the research techniques used by the various investigators. These include the application of precision stadiometry, electromyography, epidemiology, the Delphi method, dynamic goniometry and body composition analysis. The anthropometric studies from the Brussels project are summarised since the outcomes had implications for the anthropometric investigations of Belgian nurses that formed an element of the programme at Brussels. In other instances, for example the use of physiological indices of occupational strain, the application follows on directly from the literature review. In the main, individual studies illustrate how hospital specialisms fit into the broader ergonomics context. These are reported as self-contained entities in some instances, for example spinal shrinkage in the hospital porters or diurnal variation of spinal segment motion in nurses. In other instances the research findings have already been communicated and a list of publications from the project appears as an Appendix. These include the observation that an ergonomic approach which allows nurses the opportunity to adjust the height of their hospital patient's bed helps to enhance the quality of spinal motion.

The publication of this book should be of interest to ergonomists, health and safety engineers, occupational health workers and health-care professionals and educators. The work incorporated a number of deliverables for exploitation, especially those concerned with methodological approaches. These included: i) questionnaire tool for epidemiological investigations; ii) confirmed use of heart rate, oxygen uptake and spinal shrinkage in combination for ergonomic assessment of occupational load; iii) integrated motion analysis and profile of individual characteristics into formal risk assessments; iv) multidisciplinary preventive model for implementation in back-care education and reducing musculoskeletal loading. The book as a whole provides insights into the multivariate issues in musculoskeletal disorders and methods of investigating them. It serves a purpose also for research workers, for whom there are many projects in this area waiting to be undertaken. These are likely to remain a challenge to researchers for some years into the future.

Thomas Reilly Director, Research Institute for Sport and Exercise Sciences Liverpool John Moores University

Acknowledgements The success of the project concerned with musculoskeletal disorders in health-related occupations was attributable to the many people who contributed to it in one way or another. First, the award of research grant (BmH4 - CT96-1057) by the European Commission made the investigations possible. For their execution, the help of the administrative staff at the EC's offices in Brussels and in the three contributing universities is gratefully acknowledged. For the conduct of the studies a debt of gratitude is due to the research staff members who worked full-time on the project at various stages. These included Caryl Beynon, Joanne Burke, Diana Leighton, Mark Verlinden and Evert Zinzen. Thanks are due to the laboratory technical staff at each of the collaborating universities. The loan of equipment from Dr Kim Burton at the University of Huddersfield is also appreciated. Other individuals and institutions who supported components of the programme are acknowledged within the appropriate chapter of this text. The collation of the material and its organisation into a camera-ready manuscript were accomplished by Ms Lesley Roberts at the Research Institute for Sport and Exercise Sciences (Liverpool John Moores University). Her care and computing skills brought this book to completion.

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The participating institutions The Department of Experimental Anatomy at Vrije Universiteit Brussel is a basis for fundamental research of topographical, functional and clinical anatomy, polarised around the human body and its body composition. The department has a Director (Prof. Dr. Jan Pieter Clarys, e-mail: [email protected]), 10 members of staff and a full-time secretary (Mrs Jenny Mertens) and sits within the Faculty of Physical Education and Physiotherapy. Both dissections (a detailed study of the interior human body) and plastinated models (made of prepared parts of the human body) are elements of every student contact with anatomy. The research findings (anatomical variations and detailed within the experiment) keep being updated as a function of this type of education, with variable accents in clinical anatomy, anatomy in vivo and kinesiology. Furthermore, its application towards rehabilitation sciences, sport sciences (performance analysis and analysis of the human motor behaviour) and ergonomics (simulation conditions and task analysis) are domains that are explored on a continuous basis. The use of electromyography, the capture of muscular activity by means of surface electrodes, is a means of to approach and study applied biomechanics, which reveals the magnificent world of the muscles of the living body in its dynamic context. The Department of Experimental Anatomy is also home of the Manual Therapy, arthrokinematics, isokinetics, body composition and EMG scientific supported education. The facilities for study of cadavers are unrivalled elsewhere in Europe. The Brussels Cadaver Analysis Study has stimulated international collaboration, most notably with researchers in Canada and Sweden. Much of the pioneering work on kinesiological electromyography also was instigated within the department. The study of muscle function is pursued using isokinetic dynamometry, complemented by its academic programmes in manual therapy and physiotherapy. Its activities are aligned to those in human biometry and physical education at the University's Hilok campus. Research in ergonomics at the Free University of Amsterdam is conducted within the Faculty of Human Movement Sciences, in close conjunction with the University Medical Centre Nijmegen. Together these units constitute the Institute of Fundamental and Clinical Human Movement Science which is approved by the Royal Netherlands Academy of Arts and Sciences. This research institute (IFKB) was founded in 1995 and is the only research school in the Netherlands that focuses exclusively on human movement. The Dean of the Faculty is Professor Peter Hollander (e-mail: [email protected]) and the head of the Research School is Dr Huub Toussaint (e-mail: H M [email protected]). The research of the IFKB is organised around three themes. These themes are studied in historically evolved cohesive groups called research lines, which are ordered according to the themes. Each line is headed by a line co-ordinator who is responsible for the realisation of the scientific goals of the line and its financial management. The line co-ordinators form the advisory body to the board of the IFKB. An education programme committee assists the board in the evaluation of the graduate educational programme.

The object of the study of the IFKB is human movement. The research is focused on three themes, each theme comprising several research lines. The themes are: A. Physical load and capacity of the human action system B. Energy metabolism and fatigue C. movement co-ordination. This structure has stimulated the integration of knowledge within the three themes, lending itself suitable for ergonomics also. The academic programmes include a specialisation in ergonomics work. This aspect of work is supported by a vibrant enterprise culture and projects funded by national industries. The Research Institute for Sport and Exercise Sciences at Liverpool John Moores University was established in November 1997, being the first research unit formally endorsed by the Academic Board of the University with this title. The designation followed its top rating nationally in the Research Assessment Exercise of 1996 and acknowledged the international status of the research programmes in sport and exercise sciences. The Research Institute has a Director (Professor T. Reilly, e-mail: [email protected]), a Deputy Director (Professor Adrian Lees, e-mail: A.Lees @ livjm.ac.uk), an Advisory Board (made up of its Professors and Readers), a full-time Secretary/Administrator (Ms Lesley Roberts) and a membership exceeding 60 individuals. There are in excess of 40 research students (M.Phil, PhD) registered within the Institute, and a limited number of Research Studentships are advertised annually on a competitive basis. The research student body includes international students and the majority of students are externally funded or self-sponsored. The Research Institute also offers a one-year training programme leading to an MRes (Sports Science) award. The research programmes span the range of disciplines within the human sciences. There are three major areas for highlighting: i)

human performance: focuses on biomechanics, motor control, fitness evaluation, training, elite performance; there is a particular interest in science and football, and in sports ergonomics; ii) exercise and health; includes aspects of musculoskeletal disease and injury prevention, diet and nutrition, environmental stress; cardiovascular health and occupational ergonomics; iii) exercise and biological rhythms, circadian rhythms, sleep, travel fatigue, circamensal rhythms, women and exercise. There is a range of externally funded projects and supportive sponsors. Research programmes operate in harmony with the activities of the Human Performance Unit where work is related to national governing bodies, Olympic athletes and ergonomics projects. The activities are complemented by research consultancy contracts with sports industries. A wide range of activities is organised under the aegis of the Institute. These include one-day symposia, international conferences (e.g. The International Conferences on Sport, Leisure and Ergonomics held every 4 years in affiliation with the Ergonomics Society; conference of the World Commission on Science and Sports), and national scientific events (the BASES Conference in September, 2000 and the Football Association's Coaching Association Conference, November 2001).

The Research Institute also hosts each year a limited number of honorary Research Fellowships and welcomes post-doctoral and visiting professors from overseas. The Research Institute also houses the offices of the World Commission for Science and Sports. The website address of the Research Institute is www.livjm.ac.uk/hhs/RISES. Collectively the three institutions have common strands within the fields of ergonomics and other human sciences. Collaboration has been effected long term by mutual research training schemes, ERASMUS programmes and exchange visits supported by the British Council. There have also been short-term exchanges for cooperative doctoral work and sharing of research plans. This team-work culminated in the Biomed IV Programme which is the subject of this book.


Contents Preface

v

Acknowledgements

vii

The participating institutions

ix

1.

Introduction to Musculoskeletal Diseases: The Biomed IV Project T. Reilly

1

2.

The Identification and Measurement of Risk D.J. Leighton and C. Beynon

7

3.

Measurement of Spinal Loading: Shrinkage T. Reilly

25

4.

Epidemiology: Musculoskeletal Problems in Belgian Nurses E. Zinzen

41

5.

Epidemiology of Musculoskeletal Disorders in a Sample of British Nurses and Physiotherapists C. Beynon and T. Reilly

63

6.

Electromyography in Occupational Activities J.P. Clarys and T. Reilly

85

I.

The Implementation of Additional Software for 3-D Analysis of Coupled Motion in the Cervical Spine by Means of an Electromagnetic Tracking Device P. Van Roy, J.P. Baeyens, R. Lanssiers, A. Vermoesen, D. Caboor, E. Zinzen, M. Verlinden and J.P. Clary s

97

8.

A Method for Job Evaluation using a Modified Delphi-Survey D. Caboor

107

9.

Physiological Assessments of Occupational Activities T. Reilly, J. Burke, S.D.M. BotandA.P. Hollander

117

10.

Spinal Shrinkage during Simulated Nursing and Porters' Tasks C. Beynon

127

II.

The Effects of the Nurse's Job on the Diurnal Variation of the Segments of the Spine - An Anthropometric Approach D. Caboor

137

12.

Body Composition: Part I. Physical and Structural Distribution of the Human Skin J.P. Clarys and M. Marfell-Jones

143

13.

Body Composition: Part II. "Whole-Body Adiposity" Prediction: Males versus Females J.P. Clarys, A. Martin and D. Drinkwater

151

14.

Body Composition: Part III. In vivo Application of a Selection of Formulae for Predicting Whole-Body Adipose Tissue in Male and Female Nurses J.P. Clarys, K. Alewaeters and E. Zinzen

163

15.

Musculoskeletal Disorders in Health-Related Occupations: Project Overview and Outcomes T. Reilly, D. Leighton, C. Beynon, J. Burke, J.P. Clarys, P. Van Roy, E. Zinzen, D. Caboor, M. Verlinden and A. P. Hollander

171

Subject Index

187

Appendix: Publications and Communications from the Biomed IV Research Project

189

Author Index

191

Musculoskeletal Disorders in Health-Related Occupations T. Reilly (Ed.) IOS Press, 2002

INTRODUCTION TO MUSCULOSKELETAL DISEASES: THE BIOMED IV PROJECT Thomas Reilly Research Institute for Sport and Exercise Sciences LiverpoolJohn Moores University, Henry Cotton Campus 15-21 Webster Street, Liverpool, L3 2ET United Kingdom Abstract: incidence and prevalence of back pain are high in nursing personnel compared to other occupational groups and the problem may extend to other healthrelated professions and other musculoskeletal diseases. The current project was undertaken by three collaborative European institutions to investigate musculoskeletal diseases in nurses, physiotherapists and hospital-based porters. A multivariate approach was adopted and the work distributed according to the strengths of the participating research groups.

1. Background and rationale Lower back pain affects a large part of the adult population, over 60% of whom have a cumulative lifetime prevalence of the syndrome. Back pain is a very common cause of morbidity, disability and threat to health and well-being. The lower back is more commonly affected by occupational over-exertion than are other parts of the body, and accounts for about two-thirds of total occupationally related injuries. The major part of the remainder is attributable to other musculoskeletal disorders (MSD) associated with poor working postures or working practices. Such postures and manual handling practices are evident in occupations within healthcare professionals and the hospital environment. Data from the United Kingdom and Belgium emphasise the huge economic consequences to industry of certified sickness due to working days lost as a consequence of musculoskeletal disorders. Since their causes are multifactorial, it is important that an ergonomics appraisal should take an interdisciplinary approach towards identifying critical epidemiological factors. Identification of the interactions between factors would help form a strategy for reducing the incidence of musculoskeletal disorders. A decrease in prevalence would have huge economic benefits to the employers. Since these disorders adversely influence participation in leisure and recreational activities in those people affected, any improvement in the preventive practices would help preserve the health and well-being of workers, especially among the European communities.

2

T. Reilly /Introduction to Musculoskeletal Diseases: the Biomed IV Project

It was envisaged that the outcomes of the work from this research programme would have potential also for the education and training of personnel at risk of musculoskeletal disorders in the workplace. The ergonomics check-list incorporated into the preventive model (which represented the culmination of the current project) could form a basis for reducing occupationally related biological problems and thereby benefit the employer in healthcare professions.

2. Objectives and organisation of the research programme The project was focussed on health-related occupations to compare the prevalence of musculoskeletal disorders in different specialisms, identify causes of occupational strain, establish physiological indices of strain, evaluate the effects of altering typical work-rest cycles and develop a multidisciplinary preventive model. The specific objectives and primary approach were as follows:i)

ii) iii)

iv) v)

establish prevalence of musculoskeletal diseases among nurses and physiotherapists by means of an extensive questionnaire and information gained from hospital Occupational Health Department records ; identify possible causes of occupational strain using questionnaire and extensive ergonomic risk assessment within the hospital environment; establish the interaction between risk factors in the workplace environment and the incidence and prevalence of occupational musculoskeletal diseases, employing a multivariate approach to data collection; examine the physiological and biomechanical effects of alterations in work-rest schedules among hospital porters using physiological and physical indices of occupational strain; develop a model to be used in the prevention of back problems in nursing personnel based on synthesis of data collected from a variety of different tests.

The project was co-ordinated from Liverpool John Moores University and its partners included research groups from Vrije Universiteit Brussel and Free University of Amsterdam. Previous work at Liverpool had embraced epidemiological aspects of back pain in nurses and comparisons of its prevalence in the general population (Leighton and Reilly, 1995). Results for back pain and sickness absences in comparison with the general population data are shown in Table 1. The epidemiological approach was complemented by measurements of spinal loading associated with particular occupational tasks. A range of patient-transfer procedures were implicated as causative in precipitating back pain by nurses who had both indicated an annual prevalence of back pain and recalled a particular incident. The most common task implicated by the nurses was positioning a patient in bed, followed in importance by moving a patient from bed and moving a patient from a chair (Leighton and Reilly, 1995).

T. Reilly /Introduction to Musculoskeletul Diseuses: the Biomed IV Project

3

Table 1. Back pain and sickness absence figures for nursing personnel and members of the general population (from Leighton and Reilly, 1995). Nursing personnel (n = 1134)

General population (n = 315)

24.4 25.1 Point prevalence 58.8 57.8 Annual prevalence 61.4 58.9 Lifetime prevalence 14.7 11.5 Annual incidence 14.2 35.1 Sickness absence* * Number of days absent due to back pain expressed as a percentage of days lost for all causes.

The magnitude of the back-pain problem appears to have increased among nursing personnel since the results of a survey by Stubbs et al. (1983). Whilst nurses may have been singled out for detailed attention (Buckle, 1987; Garg and Owen, 1992; Pheasant and Stubbs, 1992), other professions within the health-care system are also vulnerable. These include physiotherapists (Scholey and Hair, 1989) and possibly also hospital porters. These professions were of interest in the current project. There are various techniques that are used in ergonomic analyses of occupational tasks. Once problems are identified within habitual activity profiles, the critical tasks may be isolated by formal risk assessment. The research group at Vrije Universiteit Brussel planned to follow up their epidemiological surveys with task analyses to establish the ‘Top 10’ most heavy nursing duties in bed-patient related tasks. Sophisticated opto-electronic devices are now available for detailed motion analysis which can be combined with electromyography. The main muscles associated with movements of the trunk are listed in Table 2. In addition spinal movement may be monitored in three dimensions using electrogoniometry. Using this combination of methods (and the associated computer software systems), the consequences of redesigning particular tasks could be evaluated. An example is the redesign of bedheight so that the task is harmonised to the individual. The efficacy of such an intervention requires profiling the anthropometric and individual characteristics. The eventual goal of such multivariate analysis is to establish a predictive model. Table 2. The muscles associated with movements of the trunk.

Movement

Muscles

Extension of the trunk

Erector spinae, multifidus, lumborum, interspinales.

Flexion of the trunk

Psoas major, psoas minor. Abdominal muscles: obliquus externus abdominis, obliquus internus abdominis, rectus abdominis.

Rotation of the trunk

Obliquus internus abdominis, multifidus, obliquus externus abdominis, rotatores, semispinalis.

Lateral flexion of the trunk

Obliquus externus abdominis, rectus abdominis, obliquus internus abdominis, erector spinae, multifidus, quadratus lumborum, intertransversarii.

semispinalis,

quadratus

T. Reilly / Introduction to Musculoskeletal Diseases: the Biomed IV Project

Whilst low-back pain may have been the main focus of research attention, other areas are implicated in musculoskeletal disease. Spinal loading and poor ergonomic working practices may have consequences in neck pain. Repetitive manual handling tasks might also be linked with problems in the upper limb. The syndrome of repetitive strain injury, chronic injury linked with repeated fast actions leading to pain in the musculotendinous complex, is another recognised entity. Overall physiological strain has traditionally been indicated by global measures such as heart rate and energy expenditure. Generally, the responses are averaged over an entire work-shift, the assumption being that the measures are representative of steady state conditions. The responses can be gauged against a classification system such as Christensen's (1953). The categories of work severity shown in Table 2 may be related to subjective exertion using Borg's (1970) scale. Table 3. Christensen's classification of occupational work.

Energy expenditure kcal (kJ).min'1

Heart rate (beats.min"1)

Body temperature (°C)

175

39.0

150

38.5

125

38.0

5.0 (20.9)

100

37.5

2.5(10.5)

75

37.0

Too heavy 12.5(52.3) Very heavy 10.0(41.9) Heavy 7.5(31.4) Medium Light Very light

Once physiological systems are strained, there is a need for rest to allow recovery to the original state. This necessity raises questions about the optimal work-rest ratio. If rest periods are too long, the individual worker is under-productive; in contrast, the worker will underperform if fatigued from previous physical activity. The research at Amsterdam focussed on the validity of physiological indices of work-stress in nonsteady state conditions, prior to investigations of the work-load of hospital porters. 3. Distribution of project-based work 3.1 The Liverpool project Separate epidemiological surveys were planned in order to investigate musculoskeletal disease in health-related professions. The first investigation consisted of a cross-sectional survey of nurses and physiotherapists. In the second phase of investigation a prospective study was conducted within an 'occupational health' department, also targeted at nursing personnel and physiotherapists. The surveys were designed as a prelude to an ergonomic evaluation of hospital based nursing and physiotherapy tasks. Techniques included a formal risk assessment and observation whilst shadowing individuals at their work-place.


The final phase of the work was concentrated on hospital-based porters. Their normal activities had first to be examined in order to design alternative work-rest schedules. The modifications can be examined for any benefits using a multidisciplinary approach incorporating physiological responses, subjective reactions, and physical response (spinal shrinkage). These measures are harmonised with ratings of postural discomfort whereby the affected anatomical areas are identified by the subject and discomfort is rated on a seven-point scale (Corlett and Bishop, 1976). 3.2 Vrije Universiteit Brussels The whole programme was backed up by a large relevant literature database. An epidemiological survey was planned to establish lifetime prevalence for low-back pain and neck pain in Belgian nurses. An array of individual characteristics and lifestyle factors was used to identify likely sufferers. A preventative programme could be outlined once the relative weightings of predictive variables were calculated. A comprehensive task analysis was intended to identify discrete nursing 'jobs' and isolate those that are 'heaviest'. Those 'jobs' could be evaluated in both existing and re-designed bed-patient set-ups. Force platform, motion analysis and electromyography could be combined to investigate the strain associated with the tasks that were scheduled for investigation. 3.3 Free University Amsterdam The work at Amsterdam was designed to feed into the later stages of the investigation of work-rest ratios at Liverpool. A work-cycle incorporating periodic vigorous bouts of activity, superimposed on an intermittent work-rest cycle was designed for the study of the relation between heart rate and oxygen consumption. The preliminary investigation of activity of hospital-based porters was set up for comparison with the later research at Liverpool.

4. Overview Musculoskeletal disorders are the most commonly reported occupational diseases within work-forces of the European Union. This project was focused on healthrelated occupations to compare the prevalence of musculoskeletal disorders in different specialisms, identify causes of occupational strain, establish physiological indices of strain, evaluate effects of altering typical work-rest cycles and develop a multidisciplinary preventive model. It was intended that a broad range of methodologies was to be employed in the research utilising the technical and scientific skills of the three university-based groups in the collaboration. A range of outcomes was anticipated from the research. Firstly, a new methodology for epidemiological studies was expected which would take the form of a validated questionnaire tool. Secondly, there should be an indication of how spinal shrinkage combined with conventional measures such as heart rate and oxygen uptake in ergonomic assessment of occupational load. Third, motion analysis and individual characteristic profiling were to be integrated with formal risk assessment. A multidisciplinary preventive model would have value if implemented in back care education and training for manual handling.


References Borg, G. (1970). Perceived exertion as an indication of somatic stress. Scandinavian Journal of Rehabilitation Medicine, 2, 92-98. Buckle, P. (1987). Epidemiological aspects of back pain in the nursing profession. International Journal of Nursing Studies, 24, 319-324. Christensen, E. H. (1953). Physiological valuation of work in the Nykroppa Iron Works. In: Symposium on Fatigue (edited by W. F. Floyd and A. T. Welford). London: H. K. Lewis. Corlett, E. N. and Bishop, R. P. (1976). A technique for assessing postural discomfort. Ergonomics, 19, 175-182. Garg, A. and Owen, B. (1992). Reducing back stress to nursing personnel: an ergonomic intervention in a nursing home. Ergonomics,35, 1353-1375. Leighton, D. J. and Reilly, T. (1995). Epidemiological aspects of back pain: the incidence and prevalence of back pain in nurses compared to the general population. Occupational Medicine, 45, 263-267. Pheasant, S. and Stubbs, D. (1992). Back pain in nurses: epidemiology and risk assessment Applied Ergonomics, 23, 226-232. Scholey, M. and Hair, M. (1989). Back pain in physiotherapists involved in back care education. Ergonomics, 32, 179-190. Stubbs, D. A., Buckle, P. W., Hudson, M. P., Rivers, P. M. and Worringham, C. J. (1983). Back pain in the nursing profession. 1. Epidemiology and pilot study. Ergonomics, 26, 755-765.


THE IDENTIFICATION AND MEASUREMENT OF RISK D.J. Leighton and C. Beynon Public Health Sector School of Health and Human Sciences Liverpool John Moores University 70 Great Crosshall Street, Liverpool L3 2AB United Kingdom

Abstract. Epidemiological evidence supports the existence of risk factors for workrelated musculoskeletal disorders (MSDs). Recognised risk factors include manual handling, posture, task repetition, vibration and psychosocial factors. The combination and interaction of risk factors for MSDs make assessment of exposure to risk difficult. The focus of this chapter is the development and application of a comprehensive risk assessment tool for use within a health care setting. In total, 294 individual risk assessments were performed on nurses and physiotherapists undertaking their normal work activities. The work tasks associated with the highest risk were those concerned with transferring and lifting patients and those involving a static hold. Senior physiotherapists were shown to be at greater risk than lower grade staff, as were nurses and physiotherapists between the ages of 20 and 39 years. Risk was related to the speciality in which staff worked, with the spinal injuries unit being associated with higher risk tasks. The potential risk associated with performing occupational tasks decreased after 19:00 hours for all staff. The epidemiological studies described in this chapter and elsewhere in this publication provide supporting evidence for the validity of the risk assessment tool.

1.

Introduction

The potentially hazardous nature of certain work activities is recognised in European Union legislation and the associated guidance/initiatives produced/undertaken by member states. In the United Kingdom, for example, guidance on the Manual Handling Operations Regulations 1992 (Health and Safety Executive, 1998) provides advice for employers on the identification and control of risk factors within the work environment. As a result, there has been particular interest in the performance of practical risk assessments for work-related musculoskeletal disorders (MSDs). The assessment of risk for work-related musculoskeletal disorders is dependent upon the existence of recognised 'risk factors'. It is well established that causes of MSDs are multifactorial, where a number of risk factors (physical, psychosocial, environmental, personal) singularly or in combination, contribute to the development of a condition. Substantial epidemiological research has provided evidence for the effect of specific

3

D.J. Leighton and C. Beynon / The Identification and Measurement of Risk

(mostly physical) (Li and Buckle, 1999) work activities on the development of MSDs in some body parts. This knowledge is essential, and should form the scientific basis for the development of any exposure assessment tool which aims to identify the risk associated with the performance of work activities and the incidence of MSDs. The combination and interactions of risk factors for MSDs make exposure assessment difficult. However, a risk assessment tool which incorporates physical, personal and environmental elements of the work being performed and the worker performing it, provides a comprehensive assessment from which more information concerning the potential interaction of risk factors may be gleaned. In this chapter the risk factors for which there is evidence of a causal link will be described. Similarly, the relative merits and shortcomings of a number of published exposure assessment tools will be discussed as a basis for the development of a risk assessment methodology for application in a healthcare setting. The findings from the epidemiological studies of this work programme provide supporting evidence for the validity of this risk assessment tool.

2. Epidemiological evidence for risk factors associated with MSDs 2.1 Manual handling It is widely accepted that the manual manipulation of heavy loads has the potential to cause back problems. Convincing evidence of a causal relationship between heavy physical work and back problems was acknowledged in the comprehensive review by NIOSH (1997). More specifically, repetitive lifting of heavy loads is recognised as increasing the potential for back pain by exceeding the strength of the anatomical structures involved (Videman et al., 1995). de Zwart et al. (1997) analysed repeated questionnaire data over a four-year period to evaluate a range of musculoskeletal complaints relative to work demands. For most complaints, there were significantly greater increases in prevalences for those working in heavy physical work than in the control group. 2.2 Posture Sustained abnormal postures lead to muscle imbalance, with certain muscles being overused and opposing muscles being under-used. Muscles in either a lengthened or shortened position will be at a mechanical disadvantage and gradually become weak. Certain postures render the worker more prone to this muscle imbalance (Higgs and Mackinnon, 1995). For example, symptoms in the neck and shoulder region have been linked to static muscle activity and short work-cycle time in Danish wood and furniture workers due to prolonged forward and lateral flexions of the neck in certain tasks (Christensen et al., 1995). Punnett et al. (1991) indicated that musculoskeletal problems of the back were associated with mild (21° - 45°) and severe (>45°) flexion, or lateral bend in excess of 20°. Although insufficient evidence for either the presence or absence of a causal relationship between static work posture and MSDs was noted in the NIOSH review (1997), it did acknowledge evidence of a positive relationship between posture in general and MSDs in the following anatomical areas: neck, shoulder, elbow (in combination with other risk factors such as force, repetition), hand/wrist and the back.


2.3 Repetition Due to ever increasing automation within the western world, work is becoming more repetitive with constrained ranges of motion and infrequent task rotation. This situation places sustained demands on the same anatomical area (Peate, 1994). Repetitive work is linked to problems of the neck, shoulder, elbow, wrist and hand (Ohlsson et al, 1995; NIOSH, 1997). As indicated above, repetition may interact with other risk factors (force, posture) to cause work-related MSDs. 2.4 Vibration The most pronounced long-term effect of whole-body vibration is damage to the spine. Kelsey and White (1980) reported that prolonged periods of driving increased the risk of disc prolapses and vibration was given as one of several associated causes (BieringSarensen and Thomsen, 1986). Vibration puts the back muscles under stress which is augmented by the need to maintain balance and whole-body vibration is a particular risk factor for the onset of low-back pain in drivers when coupled with other activities such as loading and unloading a truck. The back is not the only anatomical area affected. The vibration effects of handheld power tools have been linked to a variety of hand and wrist disorders, often described as hand-arm vibration syndrome, and more specifically includes carpal runnel syndrome and Raynaud's phenomenon (Bonney, 1995; Atterbury et al, 1996). 2.5 Psychosocial factors Traditionally, research has focused on the physical risk factors associated with musculoskeletal disorders (Vender et al., 1995). The multi-factorial aetiology of musculoskeletal disorders is now well recognised and psychological factors relating to the individual and the occupation must be considered (Lungberg, 1995). Similarly, Li and Buckle (1999) acknowledged the increasing evidence to support the contribution of psychosocial factors in the development of work-related musculoskeletal disorders. Psychosocial hazards can be defined as 'aspects of job content, work organisation and management and of environmental, social and organisational conditions which have the potential for psychological and physical harm' (Cox, 1993). Exposure can affect individuals directly, by physical mechanisms and indirectly, by mechanisms mediated by psychological stress. For example, noise, heat and humidity can be physically detrimental and also act as a psychological stressor. Work is usually perceived as stressful when it involves demands which can not be matched by the individual's real and perceived capabilities, especially when the workers have little or no control (Cox, 1993; Lungberg, 1995). While the study of general stress and its associated physical problems is useful, it is more valuable to discriminate occupational stresses into their causative factors to establish which exact stress factors relate to musculoskeletal disorders. Work pace (Bernard et al, 1994; Ekberg et al, 1994), work load (Ohlsson et al, 1994; Daniels and Guppy, 1995), little control of work (Leino and Hanninen, 1995; Ekberg and Wildhagen, 1996; Hemingway et al, 1997) and poor communication at work (Bernard et al, 1994; Ekberg et al, 1994; Faucett and

10


Rempel, 1994) have all been associated with musculoskeletal disorders of various anatomical regions. 2.6 Personal/Individual factors Personal characteristics and social background have also been considered in epidemiological investigations. Age (Badley and Ibanez, 1994), sex (Ohlsson et al., 1994), stature (Arad and Ryan, 1986), smoking (Frymoyer and Gordon, 1989), alcohol consumption (Arad and Ryan, 1986) and social background (income and years of schooling) (Viikari-Juntura et al., 1991) and their association with musculoskeletal symptoms have also been considered. Personal factors, such as age and sex, may be recorded during a risk assessment so that their association with the risk of the task can be ascertained. However, according to NIOSH (1997) there is little evidence to show that personal factors interact synergistically with physical factors. 3. Measurement tools 3.1 The necessity for techniques Employers have become increasingly aware of the effects that work tasks and workspace design have on the health of employees. This awareness has led to a corresponding demand for methodologies to assess work practices, both to identify problems and evaluate the effectiveness of interventions and ensure compliance with legislation (Haslegrave and Corlett, 1995). Techniques are needed to assess the demands of the work tasks and establish whether these demands constitute a risk of causing musculoskeletal problems (Haslegrave and Corlett, 1995). Risk assessments constitute a method for prioritising work-place improvements as the same procedure can be used to establish the comparative risk of different work tasks. The same assessment should be performed before and after a work-place intervention to enable such strategies to be evaluated (Li and Buckle, 1999). Three general types of measurement strategies exist for the identification of risk factors for musculoskeletal disorders; i) self-reports by workers (subjective reporting), ii) risk assessments by an individual trained in the technique (systematic observations) and iii) measurements using some instrumentation (direct measurements). Exposure to risk factors should also be expressed by all three principal dimensions reported by Burdorf and van der Beek (1999): level, duration and frequency. Li and Buckle (1999) also explained how exposure assessment methods/tools may be described in terms of sensitivity and generality and this approach will be indicated in the following sections. Self-reports by workers, for example using a questionnaire (i.e. the Nordic Musculoskeletal Questionnaire) or check-list, are useful for collecting large amounts of information and are particularly useful for the measure of psychosocial stressors (Hagberg et al., 1995). Measurement of physical factors using some instrumentation gives more specific information regarding precise work tasks. For example, myoelectric signals (EMGs) indicate the electrical activity of contracting muscles (Hagberg et al., 1995), goniometers measure angles to the vertical of body segments to assess posture (Corlett, 1995). Such direct measurements may be costly and require specialist training


11

and equipment. These methodologies are not within the scope of this chapter but are covered in part elsewhere in this book and shall not be discussed further. Numerous risk assessment procedures have been developed and validated. These can be adapted for individual purposes. Alternatively a new procedure can be developed so that the capabilities and specific working knowledge of the individual to perform the assessment can be considered (Li and Buckle, 1999). Personnel undertaking such assessments may have little training in ergonomics and so the assessments should be fairly simple with well-defined procedures (Haslegrave and Corlett, 1995). Risk assessments may be completed instantaneously or recorded on video and analysed later. If the risk assessment is to be completed instantaneously, including a large number of observations will reduce the accuracy of the observations (Kilbom, 1994). Training and pilot work must be undertaken to ensure that the risk assessments are completed reliably. For the purpose of this chapter, examples of risk assessment procedures concerned with assessing i) the physical loading of muscles as a result of manual handling, ii) assessing working postures, and iii) evaluating psychological load shall be discussed. These are the factors associated with the occurrence of musculoskeletal problems. 3.2 The assessment of physical load The NIOSH Equation (National Institute of Occupational Safety and Health) was developed in the USA and can be used to calculate the 'Recommended Weight Limit' for a given task, assuming a baseline limit of 23 kg under the best conditions; these best conditions are a sagittal plane lift, occasional lifting, good coupling (handholds), less than 25 cm vertical displacement of load, and a situation in which the lift is made at a vertical height of 75 cm from the floor and a horizontal reach distance of no more than 25 cm from the mid-point between the ankles. This is thought to represent a situation in which 90% of a healthy working population could perform lifting work over the time period without increasing the likelihood of suffering a back problem. Detailed information on specific parameters of the posture of the individual/task under study is required. This obviously gives high specificity, but no general information about the task is obtained (Li and Buckle, 1999). Whilst the NIOSH Equation is a useful guideline, it has yet to be validated and has limitations for use in a practical setting. Firstly, the equation only applies to lifting/lowering tasks and not to carrying, pulling, pushing and it only applies to tasks that are performed whilst standing. It does not take into consideration non-uniform loads or shifts in load distribution or objects with poor coupling. These two factors are important when considering nursing and physiotherapy where the 'object' is a patient; holds can be poor and the patient can be unpredictable, resulting in the load shifting position (Stobbe et al., 1988). Finally it is not designed to assess lifting single-handedly, lifting a load with more than one person, loads lifted in constrained spaces or poor conditions and unusual loads such as contaminated material (Haslegrave and Corlett, 1995). The danger of a lifting limit is that it assumes that lifting below this weight will not cause harm. 3.3 The assessment of work posture Several other direct observational procedures are available to assess the risk of different working postures, although historically such methods are time consuming and labour intensive. One of the earliest whole-body posture coding systems for industrial use was

12


developed in Finland to investigate working postures in steelworks (Karhu et al, 1977). This OWAS system (Ovako Working posture Analysis System) records the position of the back, arms and legs respectively as the first three numbers. The fourth figure indicates the load or force used and the final two digits represent the stage in the cycle or task. This procedure allows for the estimation of the proportion of time tasks require the exertion of force or the maintenance of certain postures. An assessment sheet allows for the evaluation of the likely musculoskeletal load experienced when performing a specific task. Action categories are used for prioritising interventions for various postures in relation to their estimated times of use during the working day. The OWAS approach has a wide range of uses but the results can be low in detail, rendering the method 'general' as opposed to 'specific'. Other postural risk assessment procedures exist for specific applications. For example, RULA (Rapid Upper Limb Assessment) assesses the exposure of people to postures, forces and muscle activity known to contribute to upper limb disorders (Corlett, 1995). 3.4 Psychological assessment In relation to musculoskeletal disorders, psychological measurement tools are based on the assumption that comfort/discomfort in performing a task will be related to the load on the tissues, with pain or discomfort indicating the potential for damage to tissues (Hagberg et al., 1995). Corlett and Bishop (1976) demonstrated that if a force was exerted for as long as possible until the pain was unbearable and estimates of the discomfort levels made on a scale (5 or 7 points) at intervals during the holding time, growth in feelings of discomfort were linearly related to holding time regardless of the level of force being exerted. A linear scale for discomfort therefore exists. A body map was used in the methodology to divide the body into different segments. At various predetermined times of the day, workers are asked to give the site of discomfort and a rating of discomfort from 0 to either 5 or 7 (Corlett, 1995). This simple method gives an indication of which tasks cause the greatest discomfort and which anatomical areas are most affected. This method appears to have good sensitivity and allows for the detection of fatigue at a number of sites (Hagberg et al, 1995). Psychosocial job exposure may also be obtained from self-report questionnaires or diary. However, inherent problems with such methods are validity and reliability. 3.5 Exposure assessment Whichever method is chosen for exposure assessment, it is the opinion of 'experts' reported by Li and Buckle (1999) that: • • • • •

The method has to be cheap, easy to learn and use. The method should be applicable to all sections of working life, and should take the environmental and psychosocial aspects into consideration. The measurements have to be repeatable under re-described conditions, i.e. within the range of movements normally occurring in the actual work station. The recording equipment should not interfere with the movements being recorded and should not interfere with the worker's work. The method should have high validity, reliability and sensitivity.


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Assessment data should be readily coded for computer storage and analysis.

In accordance with the above recommendations, established risk factors and methods of assessment, a comprehensive risk assessment procedure was developed specifically for the Biomed work programme. The tool was designed to be specific to the population under assessment (applicable to both patient and non-patient handling tasks) but which balanced sensitivity with generality and took into consideration the potential interaction of risk factors for musculoskeletal disorders.

4. The development of a risk assessment tool for nursing and physiotherapy tasks 4.1 Requirements for risk assessment For use in a hospital (real-time) setting, a risk assessment must be performed objectively, quickly, accurately and in a non-invasive manner. It is important that the assessment incorporates occupational, environmental, organisational and personal elements to ensure that data are collected on a range of risk factors (physical, environmental, psychosocial, occupational, personal). For the purposes of this work programme, the risk assessment procedure was to be developed to quantify the more evident factors associated with work that may be associated with musculoskeletal disorders. An attempt was made to develop a tool to identify those nursing and physiotherapy tasks with the highest risk score. Assessments had to consider the task being performed but also the environment in which the staff members were working. The risk assessment developed should be quick, instantaneous and a non-intrusive method of collecting data. 4.2 Designing the risk assessment pro-forma The paper-based risk assessment was designed as a pro-forma with six sub-sections. A large number of observed factors decreases the precision of observations (Kilbom, 1994) but including small sub-sections rather than one whole reduced this problem. The six sub-sections detailed task, posture, load, environmental conditions, the psychological state of the individual and forces acting on the wrists and fingers. A cumulative scoring system was devised, the total score indicating the overall risk of performing a specific activity. Each task/posture was awarded a score in each of the six sub-sections depending on the risk. For example, trunk flexion of 45° scored 2, compared to flexion of 90° which scored 4. A short description of the task was included at the time of recording so that a composite score was associated with specific activities. Figure 1 shows the risk assessment pro-forma.

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AGE FEMALE NURSE GRADE SPECIALITY

TASK

WALKING STANDING SITTING PUSHING PULLING KNEEL RUNNING ST. HOLD LIFTING

DOMINANT SIDE. DATE TIME WARD NO SUBJECT NO

MALE PHYSIO,

( ( ( ( (

) ) ) ) )

( ) ( ) ( ) ( )

OBJECT ALONE

( ) ( )

PATIENT 2PEOPLE

AMBULIFT WALKING BELT PAT SLIDE

DEVICES

( ) ( ) ( )

( ) ( )

MORE

( )

EASY SLIDE

( ) ( ) ( )

DESCRIBE TASK REPEATED ( STOOPING ( TWISTING ( TRUNK FLEXION ( LATERAL POSTURE BENDING ( SHOULDERS SAGITTAL ( SHOULDERS FRONTAL (

) ) ) )

2 as the severity of work increases. Nowadays shortrange radio telemetry has made the measurement of heart rate easy and socially acceptable. The heart rate response can be recorded over an entire work-shift and the data later down-loaded. Nevertheless there remains a question about how to interpret the heart rates, especially if the work schedule is complete. In several studies a linear relationship between HR and VO2 during non-steady state activities was found, but all tests were limited to progressive incremental exercise (Gilbert and Auchincloss, 1971; Fardy and Hellerstein, 1978; Fairshter et al., 1987; Matthys et al., 1996; Bernard et al., 1997). Statements about the presence or absence of a relationship between HR and VC>2 have not been tested statistically (Edwards et al., 1973; Bailor and Volovsek, 1992), or the specific nature of activities like weight-lifting (Shaw and Deutch, 1982) and karate (Collins et al., 1991) may impede generalisations. The indirect assessment of VC>2 by measuring HR has mainly been limited to steady-state exercise. Although not yet proven, a linear relationship between HR and VO2 during intermittent and non-steady state exercise is plausible. Bunc et al. (1988) concluded that the regulation of the HR at the onset of exercise might be similar to the regulation of VC>2. Several studies have indicated the time constant or mean response time for VC>2 to be similar to that for HR in the transition from rest or from unloaded cycling to a certain workload (Hughson and Morrisey, 1983; Sietsema et al., 1989; Casaburi et al., 1997), which suggests a close relationship. Furthermore, heart rate gave a close estimate of VO2 during intermittent exercise in the study of Lothian and Farrally (1995). The first aim therefore was to investigate the validity of the use of HR-response in estimating the VC>2 during non-steady state exercise. The intention was that the applicability of HR measurement to predict V02 would be extended if the relationship between HR and VC>2 during non-steady state activities can be demonstrated. 4. Summary of methodological studies for estimating VOj Dynamic and static exercise engaging large and small muscle masses were studied in four different experiments. In a first experiment, 16 subjects performed an interval test on a cycle ergometer, and 12 subjects performed a field test consisting of various dynamic leg exercises. Simultaneous HR and VC>2 measurements were made. Linear regression analyses revealed high correlations between HR and VC>2 during both the interval test (r = 0.90 + 0.07) and the field test (r - 0.94 + 0.04). In the second experiment, 14 non-wheelchair-bound subjects performed both an interval wheelchair test on a motor driven treadmill, and a wheelchair field test consisting of dynamic and static arm exercise. Statistically significant relationships were found for all subjects during both the interval test (r = 0.91 ± 0.06) and the field test (r = 0.86 + 0.09). During non-steady state exercise using both arms and legs in a third experiment, contradictory results were found. For 11 of the 15 subjects who performed a field test

T. Reilly et al. / Physiological Assessments of Occupational Activities

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consisting of various nursing tasks, no significant relationship between HR and VO2 was found (r = 0.42 + 0.16). All tasks required almost the same physiological strain, which induced a small range in data points. In a fourth experiment, the influence of a small data range on the HR-VO2 relationship was investigated: five subjects performed a field test that involved both low and high physiological strain, non-steady state arm and leg exercise. Statistically significant relationships were found for all subjects (r = 0.86 ± 0.04). Although the rvalues found in this study were less than under steady-state conditions (see Table 1), it can be concluded that VC>2 may be estimated from individual HR-VOi regression lines during non-steady state exercise. Table 1. Comparison of the group correlation coefficients (r) between HR and VC0.05). Subjects expended an average of 948.1 and 979.5 kJ.h"1 for Tl and T2 respectively. There were no differences in \E between the two trials (p>0.05); median values being 18.41 (range 15.5 to 22.8) l.min'1 and 19.2 (range 15.0 to 24.0) l.min"1. See Table 2 for results. Table 2. Recorded variables (mean ± SD or the median and the range) and the level of probability.

Heart rate (beats.min" ) VO2 (l.min-1) Energy expenditure (kJ.h"') VE (l.min-1) Perceived exertion

Normal Trial

Experimental Trial

p Value

78 (range 7 1-93) 0.75 (range 0.65-0.94) 948.1 18.41 (range 15.5-22.8) 7.6 (±1.4)

82 (range 7 1-90) 0.81 (range 0.65-0.98) 979.5 19.2 (range 15-24) 7.8 (±1.5)

0.353 0.155 0.185 0.308 0.34

5.4 Discussion The results of these methodological studies indicated a linear relationship between HR and VO2 during both non-steady state leg exercise and non-steady state arm exercise. Although the r-values were less strong than under steady state conditions, it can be concluded that the estimation of VO2 by measuring the HR is not limited to steady state exercise. The VC>2 could be estimated from individual HR-VO2 regression lines during varying non-steady state activities. The mean heart rates of the subjects in the present study of hospital porters were in the range 71-93 beats.min"1. The narrowness of the range indicated that there were relatively little disturbances from periodic bouts of high intensity activity. Even if there had been, it seems the pace of work dictated by the experimental and normal protocols allowed the subjects to maintain the physiological stress at a low to moderate severity. The simulated work schedule was modelled on observations of


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hospital-based porters going about their routine duties. It is not known if the urgency of contingent events in a realistic work setting would always allow them to do so. The energy expenditure values would amount to 7.584 MJ over an 8-hour shift for the normal condition. This corresponds to roughly three times the basal metabolic rate, even though the perception of effort was still very light. Allowing for the typical energy expenditure over the remainder of the day, the overall daily expenditure can be estimated at 12.826 MJ (3064 kcal). The manipulation of the rest breaks failed to influence the physiological responses to the simulated work-cycle. It may be that at relatively low levels of physical activity when 'fatigue' does not occur, minor alterations in work-rest schedules are not important for physiological criteria. Nevertheless, in any intermittent work schedule, the rest breaks are a relevant consideration since postural or attentional factors may lead to discomfort and boredom in the absence of breaks from duty. References Bailor, D. L. and Volovsek, A. J. (1992). Effect of exercise to rest ratio on plasma lactate concentration at work rates above and below maximum oxygen uptake. European Journal of Applied Physiology, 65, 365-369. Bernard, T., Gavarry, O., Bermon, S, Giacomoni, M, Marconnet, P. and Falgairette, G. (1997). Relationship between oxygen consumption and heart rate in transitory and steady states of exercise and during recovery: influence of type of exercise. European Journal of Applied Physiology, 75, 170-176. Borg, G. (1970). Perceived exertion as an indicator of somatic stress. Scandinavian Journal of Rehabilitation Medicine, 2, 92-98. Bunc, V., Heller, J. and Leso, J. (1988). Kinetics of heart rate responses to exercise. Journal of Sports Sciences, 6, 39-48. Casaburi, R., Whipp, B. J., Wasserman, K., Beaver, W. L. and Koyal, S. N. (1977). Ventilatory and gas exchange dynamics in response to sinusoidal work. Journal of Applied Physiology, 42, 300311. Christensen, E. H. (1962). Speed of work and its relation to physiological stress and systems of payment. Ergonomics, 5,7-13. Christensen, E. H., Hedman, R. and Saltin, B. (1960). Intermittent and continuous running. Acta Physiologica Scandinavica, 50, 269. Collins, M. A., Cureton, K. J., Hill, D. W. and Ray, C. A. (1991). Relationship of heart-rate to oxygen uptake during weight lifting exercises. Medicine and Science in Sports and Exercise, 23, 636-640. Dill, D. B. (1936). The economy of muscular exercise. Physiological Reviews, 16, 263-291. Edwards, R. H. T., Ekelund, L-G, Harris, R. C., Hesser, C. M., Hultman, E., Melcher, A. and Wigertz, O. (1973). Cardiorespiratory and metabolic costs of continuous and intermittent exercise in man. Journal of Physiology, 234, 481-497. Fardy, P. S. and Hellerstein, H. K. (1978). A comparison of continuous and intermittent progressive multistage exercise testing. Medicine and Science in Sports, 10, 7-12. Fairshter, R. D., Salness, K., Walter, J., Minh, V-D. and Wilson, A. (1987). Relationships between minute ventilation, oxygen uptake, and time during incremental exercise. Respiration, 51,223-231. Ganguly, T., Ramachandra Rao, H. P. and Raja, S. (1981). Application of physiological parameters for evolving optimum work-rest rhythm in actual place of work. Indian Journal of Medical Research, 74, 721-728. Genaidy, A. M. (1990). The physiological effects of work-rest schedules on manual lifting tasks. In: Contemporary Ergonomics 1990 (edited by E. J. Lovesey), pp. 198-208. London: Taylor and Francis. Genaidy, A. M. and Al-Rayes, S. (1993). A psychophysical approach to determine the frequency and duration of work-rest schedules for manual handling operations. Ergonomics, 36, 509-518. Gilbert, R. and Auchincloss, J. H. (1971). Comparison of cardiovascular responses to steady- and unsteady-state exercise. Journal of Applied Physiology, 30, 388-393.

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Hughson, R. L. and Morrisey, M. A. (1983). Delayed kinetics in the transition from prior exercise. Evidence for O2 transport limitation of VO: kinetics: a review. International Journal of Sports Medicine, 4, 31-39. Lothian, F. and Farrally, M. R. (1995). A comparison of methods for estimating oxygen uptake during intermittent exercise. Journal of Sports Sciences, 13,491-497. Matthys, D., Pannier, J. L., Taeymans, Y. and Verhaaren, H. (1996). Cardiorespiratory variables during a continuous ramp exercise protocol in normal young adults. Acta Cardiologica, 51, 451459. McArdle, W. D., Katch, F. I. and Katch, V. L. (1996). Exercise Physiology: Energy, Nutrition and Human Performance. Baltimore: Williams and Wilkins. Murrell, K. F. H. (1969). Ergonomics- Man and his Working Environment. London: Chapman and Hall. NIOSH (1981). Work Practices Guide for Manual Lifting. Cincinnati: National Institute for Occupational Safety and Health. Petrofsky, J. S. and Lind, A. R. (1978). Metabolic, cardiovascular and respiratory factors in the development of fatigue in lifting tasks. Journal of Applied Physiology, 45,64-68. Pheasant, S. (1991). Ergonomics, Work and Health. London: MacMillan Press. Reilly, T. and Thomas, V. (1979). Estimated daily energy expenditure of professional association footballers. Ergonomics, 22, 541-548. Sietsema, K. E., Daly, J. A. and Wasserman, K. (1989). Early dynamics of O2 uptake and heart rate as affected by exercise work rate. Journal of Applied Physiology, 67, 2535-2541. Shaw, D. K. and Deutsch, D. T. (1982). Heart rate and oxygen uptake response to performance of Karate Kata. Journal of Sports Medicine and Physical Fitness, 22,461-468. Westerterp, K. R. and Saris, W. H. M. (1991). Limits of energy turnover in relation to physical performance, achievement of energy balance on a daily basis. Journal of Sports Sciences, 9, 1-15. Wood, D. D. (1997). Minimising fatigue during repetitive jobs: optimal work-rest schedules. Human Factors, 39, 83-101.


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SPINAL SHRINKAGE DURING SIMULATED NURSING AND PORTERS' TASKS Caryl Beynon Research Institute for Sport and Exercise Sciences Liverpool John Moores University Henry Cotton Campus 15-21 Webster Street, Liverpool, L3 2ET United Kingdom

Abstract: Musculoskeletal disorders constitute the major occupational diseases reported in the European Union. Treatment of low-back pain costs more than any other disease in the working population and despite interventions the problem is still in evidence. People working in certain occupations, for example nursing, experience a particularly high prevalence of low-back pain. Long term loading of the spine is one factor associated with back pain, leading to trauma to intervertebral discs, damage to end-plates and underlying bone and nerve impingement. Spinal loading can be assessed by measuring small changes in stature with changes being directly related to the magnitude and duration of the load. Such changes are measured using precision stadiometry, an accurate assessment tool once subjects have been familiarised. The following two studies aimed to assess the effect of alterations in working practices on spinal shrinkage during nursing and porters' tasks. The aim of the study of the nurses was to compare the effect on spinal shrinkage during the course of 4 hours of simulated work when subjects had a 20min seated break or a 20-min standing break. The aim in the porters' study was to assess the effects of altered work-rest schedules on spinal shrinkage during a 4-hour simulation of porters' tasks. Shrinkage was significantly less at the end of 4 hours when the nursing subjects sat for the 20-min break than when they were required to stand. It is suggested that a period of sitting during and average shift would reduce the number of back problems experienced by nursing as a result of spinal loading due to prolonged standing. The modified work-rest schedule employed in the porters' study failed to have any effect in reducing spinal shrinkage. It is suggested that differences in the positioning and length of the breaks between the two trials were insufficient to demonstrate significant findings because 4 hours had been adopted as the trial period. Over this period the positioning and length of the breaks employed failed to show an overall effect of altering rest breaks.

1. Introduction It is estimated that 70-80% of all people living in the industrial world will suffer from back pain at some time during their lives (Biering-S0rensen, 1984; Waddell, 1987; Friedrich, 1994) with the annual incidence being around 5% (Friedrich, 1994). Treatment of low-back pain in the working aged population costs more than any other

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C. Beynon /Spinal Shrinkage during Simulated Nursing and Porters' Tasks

disease category (Peat, 1994). Hildebrandt (1995) reported that male construction workers and female nurses showed the highest back pain prevalence rates of Dutch men and women within the working population. It can be assumed that nurses in other Western countries have similar working practices and are at a similarly high risk. Buckle (1987) estimated the cost of the problem at 764,000 lost days per year. Harber et al. (1985) and Stubbs et al. (1983) quoted similar figures. Back pain therefore constitutes a huge financial burden to organisations, not to mention considerable worry to those afflicted. Most back pain is idiopathic. It is difficult to identify risk factors when the etiologic process underlying the non-specific health outcomes are not clearly understood. Identifying the factors associated with back pain is also difficult because of its multi-factorial aetiology (Lundberg, 1995). Despite this, numerous studies have attempted to identify possible risk factors with a range of causes being cited. Long term loading of the spine is one possible factor associated with back pain. Human stature varies throughout the course of a day, being greatest on rising and least prior to going to bed. This is because compressive loads on the spine during the day cause fluid to be expelled from the nucleus pulposus and bulging of the annulus (Van Dieen and Toussaint, 1993). This process leads to loss of stature. Once the compressive load on the spine has been removed, fluid is reabsorbed by the discs and stature is regained as a consequence (Helander and Quance, 1990). Long term loading and insufficient recovery may result in damage to the underlying bone and end plates and irreversible loss of disc height (Van Dieen and Toussaint, 1993). The disc loses its capability to respond to further compressive loading (Eklund and Corlett, 1984). Bulging of the annulus impinges on the nerve roots and increases the probability of pain (Eklund and Corlett, 1984). Changes in stature can be measured using a precision stadiometer, with stature being directly related to the load and exposure time (Leivseth and Drerup, 1997). Once a period of familiarisation has been undertaken by subjects, this piece of equipment has been shown to give precise, reliable measures (Eklund and Corlett, 1984; Leatt et al., 1985; Eklund, 1988). Spinal shrinkage has been measured in numerous conditions. Some work has considered differences in spinal shrinkage when varying the load acting on the spine. Eklund and Corlett (1984) reported significantly more shrinkage when subjects performed one hour of sedentary work with a 14-kg shoulder load than when the corresponding activities were repeated on a separate day without loading. Althoff et al. (1992) reported that decreases in stature were directly related to the load on the spine. Tyrrell et al. (1985) demonstrated that stature was related to the weights lifted over a large range of loads deployed in weight lifting. Others have compared differences in spinal shrinkage during sitting and standing and the beneficial effects of sitting on shrinkage are not conclusive. Magnusson et al. (1990) observed a decreased stature in a sitting position. In this study by Magnusson et al. (1990) the subjects lay down prior to testing and the shrinkage observed whilst sitting was probably due to the shrinkage naturally observed when subjects move from a supine to a sitting posture (Leivseth and Drerup, 1997). Stature loss has been measured when subjects sat for 1.5 hours in three different chairs, a stool, office chair with a lumbar support and an easy chair with a full-size backrest inclined at 110° and with a 4-cm deep lumbar support. Shrinkage was greatest in the stool, followed by the office chair but stature increased when subjects sat in the easy chair (Eklund and Corlett, 1984). A trial incorporating standing was not included in the research design

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so a comparison between shrinkage whilst sitting and standing could not be made. Only three subjects were used in this study so it is unclear what generalisations can be made. Spinal shrinkage in subjects sitting in a variety of different chairs was studied by Althoff et al. (1992) with a correction made for heel compression (Foreman and Linge, 1989). Sitting always resulted in an increased stature regardless of the chair used and it was concluded that sitting reduced spinal stress compared to standing. Static postures, heavy physical work demands, frequent bending and stooping, twisting, sudden unexpected movements, exposure to vibration and tasks involving lifting, pushing, and pulling have all been described as having the potential to cause back problems (Kaplansky et al., 1998). With the exception of vibration, nursing involves all the above components at some time. Such actions increase the compressive load on the spine and facilitate spinal shrinkage. Hospital based porters have to perform similar occupational activities. Both nurses and porters also have to spend extensive periods of time on their feet, a factor reported to be associated with low-back pain in nurses (Beynon et al., 1998). The aim in these studies was to assess the effect on spinal shrinkage of a 20-min 'sit down' break compared to a 20-min 'standing break' during a 4-hour trial of simulated nursing activities. The second aim was to assess the magnitude of spinal shrinkage of porters working under the existing hospital work-rest schedule. A modified work-rest schedule was then developed to ascertain whether spinal shrinkage could be lessened. The overall aim of the two studies was to establish whether spinal loading could be reduced using simple modifications to working practices. 2. Methods 2.1 Work profiles Work profiles were obtained for 8 nurses and 8 porters working in a District General Hospital. Each individual was 'shadowed' for 2 hours and the actions they performed were recorded every 5 seconds. The activities were standing, sitting, walking, pushing, pulling, lifting, bending and crouching. For each individual, the total duration each activity was established. Heart rate was recorded every 15 seconds over the 2-hour period using a short range telemetry system (Polar, Kempele, Finland). Mean heart rates were recorded from the work profiles. The mean heart rates of the porters varied greatly because the work they performed was totally dependent on the varying demands of different shifts on different days. The profile with the highest mean heart rate indicated the percentage of time each activity was performed in a 2-hour period and was used to form the basis of the laboratory protocol. Upon considering the nurses' profiles, one subject was eliminated from the study because the occupational demands of this subject were uncharacteristically low. The average duration for which each activity was undertaken within a 2-hour period was calculated from the remaining seven profiles. This value was used in the laboratory testing.

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2.2 Laboratory protocols Two different laboratory procedures were developed for the nursing study. In each of the 2 trials, subjects worked for 2 hours, had a break of 20-min and worked for a further 100 minutes. This regimen constituted 4 hours in total for each test as follows: 120-min work -> 20-min break -» 100-min work -> finish Both trials were identical except subjects sat during the break in trial 1 and stood during the break in trial 2. The order of testing was randomly assigned. The work-rest schedule of porters was ascertained. Porters worked an 8-hour shift with one 10-min break in the morning and afternoon and a 30-min break for lunch. A 4-hour test protocol was used to represent this with the breaks being halved accordingly. The existing work-rest schedule to be tested was as follows: 53.75-min work -> 5-min break -> 53.75-min work -» 15-min break -> 53.75-min work —> 5-min break —» finish An alternative 4-hour work-rest schedule was proposed as the second testing protocol and is as follows: 71.66-min work -» 12.50-min break -> 71.66-min work -» 12.50-min break -> 71.66min work —> finish During the rest periods of the porters' study the subjects were required to sit in the same chair each time. During both the nurses' and porters' study each subject worked for the same percentage of time in each of the two trials. The percentage of time in which subjects were resting was identical for both trials and the relative percentage of time for each activity performed was identical for both trials. Therefore, if a subject walked for 30 minutes in trial 1, the same length of time was used in trial 2. 2.3 Laboratory procedure 2.3.1 Subjects Ten female subjects participated in the nursing laboratory study. The mean age was 25 (± 3.9) years, their mean height was 166 (± 9.2) cm and their mean body mass was 63.5 (± 6.3) kg. Ten male subjects were recruited to participate as porters. The mean age was 23 (± 2.9) years, their mean height was 180 (± 5.4) cm and their mean body mass was 81.3 (± 12.7) kg. Each subject attended the laboratory on three separate occasions. On the first occasion, subjects were familiarised with the stadiometer. 2.3.2 Familiarisation Subjects required familiarisation with the stadiometer to ensure that changes in stature were due to shrinkage and not because the subject was adopting a different posture each time. The equipment and procedure were described by Althoff et al. (1992). A cross was drawn on the verbetra prominens. A camera was mounted behind the subject and connected to a linear transducer. The camera was moved up and down

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until the horizontal line in the viewer was focused on the cross on the subject's neck. Changes in the height of the camera relative to its starting height gave a measure of spinal shrinkage. When the subjects were trained in use of the stadiometer, they were required to move away from and back onto the stadiometer in quick succession and asked to resume their previous posture. If the cross on the subject's neck returned to the horizontal line in the camera viewer each time, the familiarisation was considered complete. Exactly the same procedure was used for all subjects. 2.3.3 Test sessions On the two test sessions, subjects were required to attend the laboratory having participated in no physical activity 24 hours prior to testing. Subjects were required to lie in the Fowler's position (supine with knees and hips flexed and ankles supported) for 20 min. This allowed for a period of controlled spinal unloading so fluid would be reabsorbed into the nucleus pulposus and subjects would be near their maximum height. Subjects performed both trials at the same time of the day to control for any diurnal variation. The order of testing was randomly assigned to the subjects. Because of large inter-subject variation in spinal shrinkage, subjects effectively acted as their own controls. Shadowing the nurses had shown that their activities required a greater range of actions than did those of the porters. Whilst the nurses were standing they could still be performing certain actions with their upper limbs. During the standing periods of the nurses' trials, the subjects were required to undertake one of two activities with their arms. Firstly, they were required to lay out a sheet over a table at approximately bed height, smooth the sheet over the table before folding the sheet back up. This was to simulate a nurse performing activities involving the care of a patient in a bed. Secondly subjects were required to stack books from a table at approximately waist height to a shelve approximately head height. This replicated overhead activities such as changing drips, obtaining and replacing equipment from shelving or tidying the patients' lockers. There was no lifting component included in the testing sessions because the nurses shadowed never lifted. During care of the patient in the bed, nurses usually worked in pairs so that no single nurse was bearing all the patient's weight at any one time. The usual procedure as to 'roll' the patient. A low flat box weighing 20 kg was used in this study and was either 'rolled' away from or to the side of the subject and held for a number of seconds. This manoeuvre was similar to a nurse 'rolling' a patient to attend dressings or bed bathing and so on. 2.3.4 Variables measured Pre-test data points were obtained every 2 min to elicit the individuals' natural shrinkage. These data points were extrapolated to determine the predicted shrinkage over 4 hours. Spinal shrinkage was recorded at set intervals throughout the trials and at the end of each test session. The difference between the observed and expected measure was the final value for spinal shrinkage. Heart rate was recorded every 15 seconds using a short range telemetry system (Polar, Kempele, Finland). 2.4 Analysis of data Paired t-tests were used to analyse differences in spinal shrinkage and heart rate using Minitab (version 5). A p value of 0.05 was taken to indicate statistical significance.

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3. Results The mean, standard deviance and level of probability for heart rates and spinal shrinkage for the nurses' seated trial and standing trial are given in Table 1. Significant results are highlighted. Mean heart rates for the first 2 hours and the last 100 min did not differ significantly between the two trials (p>0.05). The mean heart rate during the seated break was significantly less than the mean heart rate during the standing break (p0.05) were found (Figure 2). -LBP(N=16)

+ LBP (N=9) Thoraco-lumbar spine length Cervical Spine length SIPS height right SIPS height left SIAS height right SIAS height left Sitting Height C7-height

-

Height -

Changes in posture (mm) Figure 2. Relation between LBP and the shrinkage for the several regions.

4. Discussion In our experiment the relative shrinkage, measured as a function of the total height, was 0.6%, as a function of the sitting height 0.9%, as a function of C7-height 0.4%, and as a function of the cervical spine 1.8%. Taking into consideration the shrinkage during the first hour after getting up, our results confirm those of Reilly et al. (1984), Tyrrell et al. (1985), Leatt et al. (1987) and Kragetal. (1990).

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The changes in the height of SIAS and SIPS were very small, floating on the zero-line. According to the findings of Althoff et al. (1992) we can assume that there is a negligible contribution of the lower limb. The data of the SIPS and the SIAS confirm the reliability of the postures of the subjects for the anthropometric measurements. In addition, we noted that the changes of stature before and after the daily work were mostly influenced by the shrinkage of the cervical spine. Tondury (1974) and Penning (1978) suggested that morphology and function of the cervical discus intervertebralis change during life-time, characterised by a pseudo-degeneration of the fibres of the annulus fibrosus beginning at the age of nine. We wonder if, complementary to the hydration and dehydration process of the discs, this morphological aspect could be a reason why we found the highest shrinkage at the cervical level. The cervical intervertebral disc is not similar to the lumbar intervertebral disc with regards to morphology, biomechanics and the nature of physiological processes (Mercer and Ml, 1996). Part of the reason that these assumptions have been made, lies in the scarcity of studies which have specifically examined the structure and the function of the cervical intervertebral disc. There is evidence that the cervical intervertebral disc has a distinct morphology which reflects the biomechanics of this region. Lifting and transferring patients are essential parts of the nursing profession, and the associated loading that goes with them is perceived as very demanding and severe (Garg et al., 1992; Caboor et al., 1996). An important part of work during these tasks and manoeuvres is performed by the upper limbs , and that assumes a high level of axial compression within the cervical region caused by a considerable activity of the muscles of the shoulder and the neck. It is assumed that this functional aspect explains in part why we found the highest shrinkage at the cervical level. The nature of these data suggests that this conclusion can be extrapolated to several manual handling jobs with heavy loading. The influence of the cervical part of the vertebral column on the spinal shrinkage might also explain why we did not found a relation with LBP. The results of this study support the observations of Garbutt et al. (1990) who found no differences in shrinkage between subjects with and without low-back pain, following both running and repetitive lifting. On the other hand the clinical study of Kindle et al. (1987) in patients with ankylosing spondylitis showed a significantly reduced diurnal variation in stature for the symptomatic group, 0.34% of total body height vs. 0.68% in the control group. The ossification of the outer collagen fibres of the annulus fibrosus reduces the mobility of the intervertebral disc and reduces also the response of the vertebral column to the compressive loads associated with gravity, habitual activity and professional activity. The diurnal body oscillation observed in the asymptomatic individuals was lower than the values previously reported (Reilly et al., 1984; Tyrrell et al., 1985; Krag et al., 1990). Differences in time schedule would account for this discrepancy. Such findings highlight the complex nature of the relationship between spinal shrinkage, disc function, disc degenaration and low-back problems. Shrinkage is a time dependent phenomenon. Taking into consideration the shrinkage over the first hour after getting up and the cervical shrinkage during the job, and looking at the specific properties of the lumbar and cervical discs, this phenomenon can be influenced mostly by the lumbar spine during the first hours of the day and during the rest of the day by the cervical region. 5. Conclusions The results of this study suggest that the change in stature during the daily nursing job primarily is located in the vertebral column, and in particular due to the shrinkage of the cervical spine. This is assumed to be a primary reason why no relation between spinal shrinkage and LBP could be found, either in the male or in the female nurses. The nature of these data suggests that this conclusion can be extrapolated to several manual handling jobs

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with heavy loading. The shrinkage of the cervical spine under these loading conditions needs to be reviewed in relation to the mechanism and occurrence of neck problems. Further research can be done in terms of electromyographic studies of the shoulder and neck muscles during the performance of manual handling tasks, with respect to time-control of the shrinkage in the lumbar and cervical region of the spine. References Adams, M. A. and Hutton, W. C. (1983). The effect of posture on the fluid content of the lumbar intervertebral discs. Spine, 7, 665-671. Althoff, I., Brinckmann, P., Frobin, W., Sandover, J. and Burton, K. (1992). An improved method of stature measurement for quantitative determination of spinal loading - Application to sitting postures and whole body vibration. Spine, 17, 682-693. Caboor, D., Zinzen, E., Van Roy, P. and Clarys, J. P. (1996). Job evaluation in nursing personnel using a modified Delphi-survey. Communication to The Second International Conference on Health in the Workplace, Liverpool, UK, 2-4 April. Dehlin, O., Hedenrud, B. and Moral, J. (1976). Back symptoms in nursing aides in a geriatric hospital. An interview study with special reference to the incidence of low back symptoms. Scandinavian Journal of Rehabilitation Medicine, 8,47-53. De Puky, P. (1935). The physiological oscillation of the length of the body. Acta Orthop, Scand., 6, 338-347. Foreman, T. K. and Troup, J. D. G. (1987). Diurnal variations in spinal loading and the effects on stature: a preliminary study of nursing activities. Clinical Biomechanics, 2,48-54. Garbutt, G., Boocock, M. G., Reilly, T. and Troup, J. D. G. (1990). Running speed and spinal shrinkage in runners with and without low back pain. Medicine and Science in Sports and Exercise, 22, 769-772. Garg, A. and Owen, B. (1992). Reducing back stress to nursing personnel: an ergonomic intervention in a nursing home. Ergonomics, 35, 1353-1375. Garg, A., Owen, B. D. and Carlson, B. (1992). An ergonomic evaluation of nursing assistants'job in a nursing home. Ergonomics, 35, 979-995. Harber, P., Billet, E., Shimozaki, S. and Vojtecky, M. (1988). Occupational back pain of nurses: special problems and prevention. Applied Ergonomics, 19,219-224. Hindle, R. J., Murray-Leslie, C. and Atha, J. (1987). Diurnal stature variation in ankylosis spondilitis. Clinical Biomechanics, 2, 152-157. Krag, M. H., Cohen, M. D., Haugh, L. D. and Pope, M. H. (1990). Body height changes during upright and recumbent postures. Spine, 15, 202-207. Leatt, P., Reilly, T. and Troup, J. D. C. (1986). Spinal loading during circuit weight-training and running. British Journal of Sports Medicine, 20, 116-124. Mercer, S. R. and Jull, G. A. (1996). Morphology of the cervical intervertebral disc: implications for McKenzie's model of the disc derangement syndrome. Manual Therapy, 2, 76-81. Nachemson, A. (1981). Disc pressure measurements. Spine, 6, 314-318. Panjabi, M. M. (1977). Experimental determination of spinal motion behavior. Orthopedic Clinics of North America, 8, 169-180. Penning, L. (1978). Normal movements of the cervical spine. AmerJ.Roentgenol., 130, 317-326. Reilly, T., Tyrrell, A. R. and Troup, J. D. G. (1984). Circadian variation in human stature. Chronobiology International, 1, 121-126. Stobbe, T. J., Plummer, R. W., Jensen, R. C. and Attfield, M. D. (1988). Incidence of low back injuries among nursing personnel as a function of patient lifting frequency. Journal of Safety Research, 19, 21-28. Tondury, G. (1974). The Cervical Spine. Bern: Huber. Tyrrell, A. R., Reilly, T. and Troup, J. D. G. (1985). Circadian variation in stature and the effects of spinal loading. Spine, 10, 161-164. Videman, T., Nurminnen, M. and Troup, J. D. G. (1990). Lumbar spinal pathology in cadaveric material in relation to history of back pain, occupation and physical loadings. Spine, 15, 728-737. White, T. L. and Malone, T. R. (1990). Effects of running on intervertebral disc height. JOSPT, 139-146.


BODY COMPOSITION: PART I Physical and structural distribution of human skin J. P. Clarys and M. Marfell-Jones Department of Experimental Anatomy Vrije Universiteit Brussel Belgium Abstract: Few research groups take into account the complex and variable distribution of human skin. Twenty five cadavers were studied to update the assessment of skin dimensions: this work provided background fundamental research prior to applying findings to the body composition assessment of nursing personnel. Comparisons were made between different segments and between males and females. Systematic differences, i.e. skin thickness, weight, volume and density, between segments and between the sexes were found.

1. Introduction In medicine, variations in physical and structural dimensions of the human skin are associated with endocrinological diseases and congenital syndromes. In physiotherapy the knowledge of skin characteristics is important for electrotherapy and decubitus treatment, while in anthropology it is an essential part of anthropometric and body composition studies. Bischoff (1863) presented a study of skin weights of two adults and later von Liebig (1874) added similar information, again based on a limited number of cadaver subjects. For over a century, many studies have been conducted on skin tension and elasticity, both on the living and on cadavers, and in different age groups (Schmidt, 1891; Reizenstein, 1894; Lindholm, 1931; Ejiri, 1938; Sodeman and Buch, 1938; Hill and Montgomery, 1940; Dick, 1947; Strobel, 1948; Kirk and Kvorning, 1949; Ma and Cowdry, 1950; Lee, 1957, 1967; Ragnell, 1957). Despite these studies, the overall physical dimensions of the skin have received scant mention in textbooks and periodical literature (Leider and Buncke, 1954; Lee, 1957; Baker et al., 1958; Booth et al., 1966; Doyle, 1969; Billznak et al., 1975). Data on absolute and comparative thickness, regional topography, volume, density, total body and segmental weights of the skin do not seem to have loomed important enough to have excited much interest or comment among dermatologists, physiotherapists, endocrinologists or anatomists. In a joint venture undertaken at the Vrije Universiteit Brussel, with Simon Fraser University Canada, 25 cadavers were completely dissected into their major tissues for the purpose of making up to date human body composition analyses

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(Clarys et al., 1984; Clarys and Marfell-Jones, 1986a, 1986b). Another joint venture was undertaken with the University of Gotenborg, resulting in another 9 whole-body cadaver dissections with tissue data acquisition. For a state of the art of adult dissection processing, we refer to the review of Clarys et al. (1999). Data of 17 cadavers have been used in subsequent skin analyses and calculations. 2. Material and methods Prior to the dissection, the cadavers were marked and measured anthropometrically including skinfolds. The marks of the skinfold were used after dissection to measure skin thickness. The cadavers were dissected into six segments: head, trunk, upper and lower limbs according to a slightly modified segmentation technique as described by Clauser et al. (1969) and Dempster (1955). As pieces of skin were dissected, they were placed immediately into airtight plastic containers, one for each of the six body segments. Eventual excess of adipose tissue adhering to the skin was scraped off prior to the physical measurements. It was observed that skin shape could be distorted by stretching, but it appeared that dimensions were little affected. This was investigated by marking 10-cm squares on the segmental skin pieces before dissection and remeasuring these after dissection. There was no indication of substantial changes in dimensions. The areas of the skin tracings were determined by planimetry in order to validate human body surface area formulae. These results are presented in Martin et al. (1984). Subsequently, skin thickness was measured (on double layer) at the marked (external) skinfold locations using a Harpenden caliper, while total and segmental skin was weighed in air and water for volume and density determination. 3. Results and discussion The mean skin thickness values per region (corresponding to the classical skinfold locations) and for both left and right sites are listed in Tables 1 and 2, respectively. Values are included for males and females. The mean weight of the skin per segment, and the contribution as a % of total segmental weight, as a % of skin weight of the whole body and as a % of total body weight are shown in Table 3 for each sex separately. Corresponding skin volumes are indicated in Table 4 while mean values of segmental densities are shown in Table 5. From Tables 1 and 2 we can see that, on the average, the skin thickness is greater in males than in females. The findings of Billznak et al. (1975), and Leider and Buncke (1954) are thereby confirmed. If we consider skin thickness per region and at the locations where the classical cutis-subcutis "skin fold" measurements are taken, the same tendencies are found between male-female and left-right, except for the pectoral chest thickness. Probably because of an important increase of connective tissue, we see an average of +2.65 mm in females and +2.45 mm in males at the chest region. The greatest skin thickness for both sexes is to be found in the subscapular region while the smallest is situated in the upper limb.

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In contrast to the variability of "classical skin folds", the skin thickness shows a relative constant distribution left and right both in males and females. In terms of skin contribution to the cutis-subcutis skinfold, we found that in men +19.5% of a skinfold is skin. For women this is +11% (average for all measured sites). Reflecting the skin thickness findings, the total and segmental skin weights are higher in males than females (Table 3 and Fig. 1), although the data are, on average, lower than those presented by Leider and Buncke (1954). Skin weight contributed relatively little to total segmental weight (TSW) and total body weight (BW). Table 1.

Mean skin thickness per region, left and right in males (mm).

Male

Left

Region Subscapular Triceps Biceps Forearm Pectoral chest Axillary chest Mid-axillary line Supra-spinae Ventral thigh Medial thigh Dorsal thigh Supra-patellae Medial calf Total mean

Table 2.

Mean 4.06 2.42 1.55 1,50 2.47 2.70 2.87 2.04 2.22 1.81 2.41 2.25 1.71 2.30

SD 0.78 0.63 0.22 0.40 0.44 0.58 0.59 0.47 0.58 0.51 0.56 0.65 0.38 0.67

Max 5.00 3.10 1.90 2.20 3.20 4.50 3.90 2.70 3.10 2.60 2.80 3.20 2.20 4.06

Right Min 2.90 1.60 1.20 1.10 1.90 2.00 2.10 1.20 1.50 1.20 1.30 1.40 1.20 1.50

Mean 4.11 2.61 1.60 1.52 2.45 2.82 3.11 2.54 2.42 1.75 2.44 2.35 1.78 2.42

SD 0.68 0.79 0.40 0.41 0.51 0.46 0.53 0.63 0.60 0.42 0.55 0.71 0.45 0.70

Max 5.10 3.90 2.00 2.10 3.30 3.30 3.70 3.50 3.30 2.50 3.10 3.40 2.50 4.11

Min 3.10 1.30 1.00 0.90 1.60 2.10 2.50 1.40 1.40 1.40 1.40 1.50 1.00 1.51

Mean skin thickness per region, left and right in females (mm).

Female Region Subscapular Triceps Biceps Forearm Pectoral chest Axillary chest Mid-axillary line Supra-spinae Ventral thigh Medial thigh Dorsal thigh Supra-patellae Medial calf Total mean

Right

Left Mean 3.47 2.02 0.98 1.20 2.68 1.95 2.72 1.87 1.86 1.63 2.18 1.82 1.57 1.99

SD 0.64 0.45 0.21 0.21 0.58 0.76 0.65 0.37 0.28 0.29 0.36 0.41 0.23 0.66

Max 4.20 2.60 1.30 1.50 2.30 3.60 3.70 2.20 2.20 2.10 2.70 2.50 1.80 3.47

Min 0.22 1.00 0.80 0.90 1.80 1.30 .70 .10 .50 .20 .60 .40 .20 0.98

Mean 3.41 2.25 1.00 1.20 2.64 1.80 2.72 1.95 2.02 1.56 2.12 1.97 1.57 0.98

SD 0.62 0.63 0.22 0.16 0.69 0.57 0.49 0.15 0.17 0.26 0.53 0.38 0.19 0.64

Max 4.40 2.90 1.30 1.50 3.80 2.80 3.30 2.20 2.20 1.90 2.90 2.50 1.90 3.41

Min 2.50 0.90 0.70 1.00 1.60 1.20 2.00 1.80 1.70 1.10 1.20 1.30 1.40 1.00

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Table 3.

Male Head L. arm R. arm L.leg R.leg Trunk Total Female Head L. arm R. arm L.leg R.leg Trunk Total

Average skin weight (SW) per segment and as a % of total body skin weight (TBW), total segmental weight (TSW) and total body weight (BW), in male and female cadavers.

SW(g)

% of TSW

%ofBW

7.5 7.8

8.5 8.3 8.3

0.6 0.4 0.4

738 715 1310 3757

19.6 19.0 34.9

5.7 5.8 4.3

1.1 1.0 1.9

100

5.5

5.5

299 213 214

9.4 6.7 6.8

7.3 7.3 6.9

0.5 0.3 0.3

642 627 1148 3167

20.3 19.8 36.2

5.4 5.4 4.1

1.0 1.0 1.8

100

5.1

5.1

405 281 292

% of TBW 10.8

An identical situation is found for skin volumes (Table 4 and Fig. 1). However, the contribution of skin volume to total segmental volume (SeV) and total body volume (T.B.V.) was not significantly different between the sexes, confirming the constancy of the skin tissue. Higher skin density averages were found for men in all segments (see Table 5). It can be concluded that there are systematic differences in skin dimensions between males and females. These differences, however, were small in comparison to the differences of the other body components (Fig. 2). In this situation, only bone approaches the body composition constancy of skin.

Figure 1. Weight, volume and density per segment of human skin.

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% IBM

DMale H Female

40 30 20 10 -

Skin

Adipose

Muscle

Bone

Residual

Figure 2. Masses of skin, adipose tissue, muscle, bone and residual as percentages to total body mass (% TBM).

Finally, if masses of skin, muscle, bone and viscera are presented as percentage of adipose-tissue-free mass (ATFM), the previous absolute value interpretation is reversed for skin, bone and residual masses (Fig. 3). This finding highlights the significance of the adipose tissue mass within the body, both male and female.

50 -

% ATFM DMale 0 Female

40 30 20 10 -

0

Skin

Muscle

Bone

Residual

Figure 3. Masses of skin, muscle, bone and residual, as percentages of adipose - tissue - free mass (% ATFM).


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Table 4. Mean skin volume (SV) per segment and as % of total skin volume (TSV), total segmental volume (SeV) and total body volume (TBV) in male and female cadavers. Male Head L. arm R. arm L.leg R.leg Trunk Total Female Head L. arm R. arm L.leg R.leg Trunk Total

SV (ml) 402 274 283 720 702 1268 3650

% of TSV 11.0 7.5 7.8 19.7 19.2 34.7 100

% of SeV 8.7 7.7 9.1 5.6 5.7 4.0 5.4

%ofBV 0.6 0.4 0.4 1.1 1.0 1.9 5.4

301 211 212 643 631 1133 3133

9.6 6.7 6.8 20.3 20.1 36.2 100

7.7 7.1 6.7 5.2 5.2 3.8 4.9

0.5 0.3 0.3 1.0 1.0 1.8 3.9

Table 5. Mean skin densities (Sd) per segment (g.mr1). Sex Segment Head Left arm Right arm Left leg Right leg Trunk

Female

Male Sd .046 .056 .061 .052 .052 .064

SD 0.011 0.011 0.010 0.010 0.011 0.010

Sd 1.026 .040 .047 .036 .039 .047

SD 0.010 0.014 0.011 0.016 0.013 0.013

Male + Female SD Sd .035 0.014 .047 0.015 .054 0.012 .043 0.016 0.014 .045 .055 0.014

References Baker, P. T., Hunt, E. E. and Sen, T. (1958). The growth and interrelations of skinfolds and brachial tissues in man. American Journal of Physical Anthropology, 16, 39-58. Billznak, J. M. D., Tom, W. and Staple, M. D. (1975). Roentgenographic measurements of skin thickness in normal individuals. Radiology, 118, 55-60. Bischoff, E. (1863). Einige Gewichts und Trockenbestimmungen de Organe des menschlichen Korpers. Zeitsch.fir rationelle Medizin , 3, 75. Booth, R. A. D., Goodard, B. A. and Paton, A. (1966). Measurements of fat thickness in man; a comparison of ultra-sound, Harpenden calipers and electrical conductivity. British Journal of Nutrition, 20, 719-725. Clarys, J. P., Martin, A. D. and Drinkwater, D. T. (1984). Gross tissues weights in the human body by cadaver dissection. Human Biology, 56, 459-473. Clarys, J. P. and Marfell-Jones, M. J. (1986a). Anthropometric prediction of component tissue masses in the minor limb segments of the human body. Human Biology, 58, 761-769. Clarys, J. P. and Marfell-Jones, M. J. (1986b). Anatomical segmentation in humans and the prediction of segmental masses from intra-segmental anthropometry. Human Biology, 58, 771782. Clarys, J. P., Martin, A. D., Marfell-Jones, M. J., Janssens V., Caboor D. and Drinkwater, D. T. (1999). Human body composition: A review of adult dissection data. American Journal of Human Biology, 11, 167-174. Clauser, C. E., McConville, J. T. and Young, J. W. (1969). Weight, volume, and center of mass of segments of the human body. Wright-Patterson Air Force Base, Ohio.


Dempster, W. T. (1955). Space requirements of the seated operator, Wright-Patterson Air Force Base, Ohio. Wright Air Development Center TR 55-159, AD 87892. Dick, J. C. (1947). Observations on the elastic tissue of the skin with a note on the reticular layer at the function of the dermis and the epidermis. Journal of Anatomy, 81, 201-211. Doyle, F. M. (1969). Radiological measurements of skin thickness and bone mineral. Scientific Basis of Medicine. Annual Reviews, 139-145. Ejirl, I. (1938). Histology of the human skin : II. On differences in the elastic fibers of the skin according to sex and age. Abs. in Arch. Dermat. and Syph., 37, 664. Hill, R. and Montgomery, H. (1940). Regional changes and changes caused by age in the normal skin. J. Invest. Dermat. 3, 231-245. Kirk, E. and Kvoming, S. A. (1949). Quantitative measurements of the elastic properties of the skin and subcutaneous tissue in young age and old individuals. J. Geront., 4, 273-284. Lee, M. M. C. (1957). Physical and structural age changes in human skin. Anat. Rec. 129, 473494. Lee, M. M. C. and Ng, C. K. (1965). Postmortem studies of skin fold caliper measurement and actual thickness of skin and subcutaneous tissue. Human Biology, 37, 91-103. Liebig von, G. (1874). Gewichtsbestimmungen der Organe des menschliches Korpers. Archiv. F. Anat. Physiol. u. Wissensch. Medizin, 96-117. Leider, M. and Buncke, C. M. (1954). Physical dimensions of the skin. Arch. ff. Dermat. and Syph. 69, 563-569. Lindholm, E. (1931). Uber die Schwankungen in de verteilung de elastichen Fasern in de menschlichen Haul, als Beitrag zur Konstitutionspathologie. Frankfurt Zeitschrift 42; 394-414 cit. in Lee, M.M.C. (1957) Physical and structural age changes in human skin. Anat. Rec. 129; 473-494. Ma, C. K. and Cowdry, E. V. (1950). Ageing of the elastic tissue in human skin. J. Geront., 5, 203-210. Martin, A. D., Drinkwater, D. T. and Clarys, J. P. (1984). Human body surface area: validation of formulae based on a cadaver study. Human Biology, 20,475-488. Ragnell, A. (1957). The tensibility of the skin: An experimental investigation. Plastic and Reconstructive Surg. 14; 317-323 - cit. in Lee, M.M.C. Physical and structural age changes in human skin. Anat. Rec. 129, 373-394. Reizenstein, A. (1894). Uber die Altersveranderungen der elastichen Fasern in de Haul. Monath. F. prakt. Dermat. 18, 1-7. Schmidt, M. B. (1891) Uber die Altersveranderungen der elastichen Fasern in de Haut. Virehows Arch.f. Path. Anat. 125, 239-251. Sodeman, W. A. and Buch, G. E. (1938). A direct method for the estimation of skin distensibility with its application to the study of vascular states. Journal of Clinical Investigation, 17, 785793. Strobel, H. (1948) Die Gewebsveranderungen de Haut im Verlaufe des Lebens. Arch. ff. Dermat. and Syph. 186,636-668.

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BODY COMPOSITION: PART II "Whole-Body Adiposity5' prediction: Males versus Females J. P. Clarys, A. Martin and D. Drinkwater Department of Experimental Anatomy Vrije Universiteit Brussel Belgium

Abstract: The skinfold is a central factor in adipose tissue patterning and for monitoring adiposity in males and females. The interest in skinfolds, given the easy accessibility of the subcutaneous layer and its non-invasive nature, has led to a proliferation of "skinfold formulae" again both for men and women separately. To obtain data to investigate human body composition, particularly the determination of whole-body adiposity, an extensive cadaver dissection study was undertaken on 34 subjects (17 females, 17 males). In addition, 40 elderly "living" subjects of the same age range were compared with the cadaver population and no significant macro-morphological differences were found, particularly in females. The available data have clearly demonstrated that skinfold compressibility is by no means constant. Adipose tissue patterning by assessment of skinfold thickness using calipers and incision confirms significant sex differences but emphasises the neglected importance of skin thickness. It appears that the best adipose tissue predictors are different from those used in general. Also the problem of estimating body fat content by skinfold is compounded by the fact that two identical thicknesses of adipose tissue may contain significantly different concentrations of fat. Skinfolds are significantly related to external (subcutaneous) adipose tissue. However, the relation to internal adipose tissue is less evident for men than for women. The sample specificity of skinfold formulae to predict whole-body adiposity is in part a result of the wide variations in compressibility, internal to subcutaneous adiposity ratios and adipose tissue composition. The data of this study clearly suggest that it is unreasonable to introduce further error by transforming anthropometric values into % of body adipose tissue in males. On the other hand, this study has demonstrated that skinfold predictions of whole-body adipose tissue in women allow for a more confident application.

1. Introduction Body composition and the assessment or prediction of whole-body adiposity - mostly referred to as "total body fat" - in particular, is a common, popular and at the same time an important ingredient of physical anthropology, medicine, sport science (Fig. 1) and more specifically of kinanthropometry, biomechanics and auxology. The most

151

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J.P. Clarys et al. /Body Composition: Part II

Figure 1. Application areas for body composition.

common methods for estimating total body fat are densitometry, whole-body potassium counting, body water measurement, anthropometry (e.g. skinfolds) and more recently, computerised tomography and magnetic resonance imaging (MRI). Anthropometry, however, relies for its validation on one or more of the other techniques and is therefore a doubly-indirect method. Skinfold measurements and quantities derived from them are used in physiology, anatomy, endocrinology, nutrition, health and fitness, growth, sport and exercise sciences. They have specific applications in occupational biomechanics, human hydrodynamics, drug quantification, diabetes, coronary heart disease, hypertension, anorexia nervosa and in many epidemiological and human body biological studies. The skinfold is a central factor in adipose tissue patterning (Edwards, 1951; Garn, 1955, 1971; Mueller and Stallones, 1981; Mueller, 1985), in "fat" distribution studies, in somatotyping (Heath and Carter, 1967 and others) and in the commercialised O-scale system (Ross and Ward, 1984) for monitoring adiposity and proportional weight. The skinfold is an essential measure to identify male-female gender and ageing differences. The interest in skinfolds, given the easy accessibility of the subcutaneous layer and its non-invasive nature, has led to a proliferation of "skinfold" applications and formulae. In the literature, over 1000 articles can be found dealing directly or indirectly with skinfold measurements, both in applied and fundamental research. Altogether more than 100 equations to predict "body fat" from skinfolds have been produced (Lohman, 1981; Martin et al., 1985; Clarys et al., 1987; Clarys et al., 1999). In spite of this proliferation of techniques for the in vivo determination of body composition, the fact remains that none of the approaches for estimating body fat has been validated against cadaver dissection. Even beyond the issue of validation, data on directly weighed body compartments are sparse. These limited data have been reported over a period of 150 years, some in obscure periodicals and in languages other than English. Results of 25 dissections of older Belgians, along with a brief summary of previously published data have been previously reported (Clarys et al., 1984). Subsequently, two further projects included nine more whole-body dissections (Clarys and Marfell-Jones, 1986; Janssens et al., 1994). In addition,


153

further 19th century data have been located, thus giving a total of 51 adults for whom body weight and the major tissue weights are known (Clarys et al., 1999). These studies, known as the Brussels Cadaver Study (CAS), were a joint venture between Simon Fraser University, Burnaby (Canada), Goteborg University (Sweden) and the Free University of Brussels, Belgium. Although body composition analysis has become increasingly popular, dissection data are sometimes difficult to access. Published data that include the weights of skin, adipose tissue, muscle and bone, along with body weight, have been reviewed (Clarys et al, 1999). The 31 men and 20 women included 34 cadavers from three separate dissection studies in Brussels, 12 from 19th century reports, and 5 from the United States. Men differed from women in that they had less adipose tissue and more muscle. The body mass index (BMI) did not differ between the sexes, because lower weights of muscle and bone compensated for the greater adiposity in women (Fig. 2).

,r

Women

Women

Figure 2. Major human body tissue weights in kg and expressed as a percentage of total body weight in men (N=17) and women (N=17).


154

Men

Skin

Muscle

Women

Bone

Skin

Muscle

Bone

Figure 3. Normalised tissue weights expressed as a percentage of adipose tissue free weight (ATFW).

The composition of the fat-free weight (FFW) and adipose tissue free weight (ATFW) (Fig. 3), though less variable than body weight, showed enough variability that the assumption of constancy of the fat-free body, required for densitometry and other indirect methods of fat estimation, could not be supported. It is the purpose of this present study to analyse the pooled data of CAS to allow a review of hazards and steps in the transformation from caliper readings to whole-body adipose tissue mass.

2. The Brussels Cadaver Analysis studies 1979-1999 - Methods The data are from three separate whole-body dissection projects, details of which have been published elsewhere. In the original Brussels Cadaver Analysis study, 13 female and 12 male cadavers, age range 55-94 years, 12 embalmed and 13 unembalmed, were selected from about 75 cadavers on the basis of least emaciation and most normal appearance (Clarys et al., 1984). After comprehensive anthropometry, each cadaver was dissected into skin, adipose tissue, muscle, bones, organs and viscera. Tissues were separated by six body segments: arms, legs, head and trunk. The weight of any fluid separating from the tissue was added back to the tissue weight. All tissues were stored in airtight humidified containers until weighing. The evaporative weight loss occurring through the dissection process, taken to be the difference between predissection body weight and the sum of all tissues after the dissection, was added back to each component in proportion to its weight. Volumes and densities of all tissues were determined by weighing the tissues underwater. One complete dissection lasted about 10-15 hours and required a team of about 12 people. The second study was undertaken to measure the composition of body limb segments and to derive prediction equations for segment weights of skin, adipose tissue, muscle and bone (Clarys and Marfell-Jones, 1986). For these purposes incomplete dissections were sufficient. However, for three subjects full dissections were completed, with a similar protocol to that of the initial study. The three subjects were two 16 year-old males and an 80 year-old female. The third study investigated the relationship between body composition estimated by computed tomography and values obtained by dissection and weighing of tissues


155

of three male and three female cadavers, age range 72-88 years (Janssens et al., 1994). The cadavers were dissected into the same components as previously. For all of the subjects, body height was estimated from the supine length measurement according to a previously-derived equation (Martin et a/., 1984). Pooling all Brussels data yielded a data set of 34 cadavers. These consisted of 17 males and 17 females, with an age range of 16 to 94 years. An immediate question that can be raised concerns the validity of applying the relationship found in such a sample to the living. If there are changes in circumferences and segment composition, these changes should be detectable by anthropometry. The relationships should not change to any marked extent, only the absolute values. It is a major assumption of this study, therefore, that the relationship between anthropometric variables and segment composition in cadavers is similar to their relationship in the living. We have therefore measured in vivo 18 elderly male and 22 elderly female subjects ranging in age from 55 to 92 years (age match selection). Using a selection of anthropometric measurements employed also in the cadaver sample and determining the somatotype of both the cadaver group and the "living" subjects according to the Heath and Carter (1967) technique as adapted by Duquet (1980), an overall comparison of the physique of post-mortem and living Belgian subjects of a similar age group was attempted (Fig. 4). Apart from a few single measurements it appears that both embalmed and unembalmed cadavers can be used to approximate these relations in the living; in other words, the use of embalmed cadavers, as opposed to fresh cadavers, will not affect the predictive ability and validity of the models and conclusions generated from the cadaver data.

CIRCUMFERENCES

FEMUR HAUEOLUS ACBOHIAL THORAX (Frontal) THORAX'(Sa?iUl) IL1ACAL SUPINE SUSPENDED

Figure 4. Normalised anthropometric comparison between age matched in vivo (zero axis) and post mortem subjects (^Vembalmed women; D unembalmed women; & embalmed men; O unembalmed men).

156


3. Results and discussion Based on the pooled data from CAS, we have been able to review step by step the combined facts, assumption and hazards to be taken into account in the transformation of skinfolds to whole-body adipose tissue mass. This approach will allow also a discrimination between men and women. The measurement of subcutaneous "fat" with skinfold calipers has become a routine laboratory and field method of assessing body composition and nutritional status. Hagar (1981) stated that "... two important assumptions must be made in the calculation of body fat from skinfold measurements: (1) subcutaneous fat constitutes a constant proportion of total body fat over all ranges of body weight, and (2) the sites of measurement are representative of all subcutaneous fat". This is at least doubtful. What is really being measured is the thickness of a double fold of skin and compressed subcutaneous adipose tissue. To infer from this the mass of fat in the body requires another series of assumptions whose validity has never been seriously challenged (Clarys et al., 1987). The evidence is available to test the validity of the transformation. In order to review the (old and new) assumptions associated with the caliper adiposity transformations, we refer to our previous "step by step" model (Martin et al, 1985; Clarys et al., 1987) as shown in Fig. 5.

Figure 5. The CAS step-by-step model of the transformation from caliper measurement to whole-body adipose tissue. (*AT = Adipose Tissue).


The transformation from caliper reading to total body fat can be divided into a number of steps. The thickness of a compressed double layer of skin and subcutaneous adipose tissue should be representative of the uncompressed double layer of adipose tissue. This should indicate total subcutaneous adiposity. This adiposity must be converted into a whole-body value and thus include fat and the internal fat. Assumption I-constant compressibility The decline in caliper reading after the initial application of the caliper to the skinfold is familiar to all users of skinfold calipers. This dynamic aspect of caliper use has been documented but given little investigative attention but it is general knowledge that the compressibility of the calipers shows an exponential decrease in reading over the first minute. Most workers adopt some strategy to standardise the reading in spite of its dynamic characteristics. Some wait "for all needle movements to cease before taking the reading" while others record after "an initial rapid phase of the movement" or read the dial after 2 or 4 s of applied pressure. In addition to the dynamic compressibility, there is also a static component to compressibility (Fig. 6). Even after standardising the timing of the caliper reading, similar thicknesses of adipose tissue may yield different caliper values due to different degrees of tissue compressibility. Since the Brussels CAS data include both skinfold thickness and the direct measurement, after incision, of the thickness of the subcutaneous adipose tissue layer, skinfold compressibility could be calculated directly at each site. Compressibility is defined as: (incised depth - 1/2 caliper reading) 100 x

Incised depth

Figure 6. Skinfold compressibility... double skin... double subcutaneous adipose layer (Courtesy of Int. J. Obesity).

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J.P. Clarys et al. /Body Composition: Part U

Skinfold site Figure 7. Compressibility means for a series of commonly used skinfolds.

Means for all subjects are shown graphically in Fig. 7. The available data clearly demonstrate that skinfold compressibility is by no means constant. This has important implications and the Brussels study included several examples, including two male cadavers with almost identical dissected adiposities of 27.1 and 27.8%, whose skinfold caliper readings at the seven commonly used sites show wide differences in compressibility, in turn resulting in very different predicted (anthropometrical) adiposities. Assumption II - skin thickness in negligible or a constant fraction All skinfold measurements contain a double layer of skin of unknown thickness. If this is very small in comparison to the skinfold measurement then its influence may be negligible. Data on skin thickness are sparse. A comprehensive review of skin thickness and surface data was completed by Clarys et al. (1988). The effect of the variability of skin thickness on skinfold values has never been seriously assessed. Since the doubled skin thickness is generally of the order of a few millimetres, it would appear that the effect of skin would be most marked at those sites and in subjects with little adipose tissue. The site where the effect of skin thickness was most marked is the subscapular, where skin thickness accounted for 28.1% of the skinfold reading (34.0% for males, 23.9% for females). Two of the most commonly used sites for predicting body fat, the subscapular and triceps, were found to have quite different proportions of skin (Clarys et al., 1987). While the contribution of skin to total skinfold thickness is generally not large, it may lead to significant error, especially in lean males. Normalised as a percentage of total adipose tissue free mass (ATFM), it can be noted that skin may have an important contribution (Fig. 3). Sites where skin thickness is small relative to skinfold might prove better predictors of adiposity. Consequently, on the basis of skin thickness, the subscapular skinfold should be a poorer predictor than the skinfold at arm and leg sites. Assumption III-Fixed adipose tissue patterning "Fat patterning" refers to differences in the anatomical placement of adipose tissue (Mueller, 1985). For reasons mentioned hereafter, the term "fat" should be replaced


by "adipose tissue". The patterning of subcutaneous adipose tissue is known to exhibit very large variations between individuals (Mueller and Stallones, 1981). To assess the value of various sites as predictors of subcutaneous adiposity, correlations between the caliper and incision thickness with the dissected subcutaneous adipose tissue mass have been determined (Clarys et al., 1987). An unexpected finding is the high correlation for lower limb sites. Of the six best sites, all but one were on the lower limb. The triceps, a highly favoured site for "fat" prediction and considered to be the best single indicator of adipose tissue (e.g. in digitised commercial devices), ranked a poor eleventh. As would be expected, correction for skin thickness for both caliper and incision values improved the correlations in 17 out of the 28 values, but it must be noted that most of the improvements were marginal. The best predictors were front thigh, medial calf, rear thigh and supra-spinale confirming in part the calculated findings of Martin (1984). This finding suggests that the common-sense approach of selecting sites from all important storage levels - e.g. segments, and especially the legs - is well founded. Assumption IV- the fat in adipose tissue Even if the mass of subcutaneous adipose tissue was known exactly, the prediction of subcutaneous fat mass requires some assumption concerning the fat content of adipose tissue. Reported values range from 5.2 to 94.1% (Martin, 1984), but they are generally in the range 60-85%. Besides, the fat content of adipose tissue increases with increasing adiposity. In view of considerations such as this, compounded by the fact that "fat" is ether-extractable, while "adipose tissue" is an "anatomical-morphological" entity, we should not use "fat" terminology in the anthropometric prediction of adiposity or not mix chemical fat in the anatomical adipose tissue studies as is too often the case still. Assumption V - the linear relation between internal and external adipose tissue From evidence based on cadaver studies it is assumed that, both in male and female subjects, the excess of adipose tissue is piled up subcutaneously, inter-muscular and internally, mostly in the trunk. The amount of intra-muscular fat in the obese should not be underestimated and should therefore be considered as a third compartment. However, in our cadaver analysis and for this purpose, the intramuscular amount has been allocated to the internal adipose tissue. Skinfold calipers are only able to estimate subcutaneous adiposity. In order to estimate total body adiposity some assumption must be made about the relation between internal and subcutaneous adipose tissue. If internal adiposity stores are proportional to subcutaneous fat, this relationship provides a rationale for use of skinfold calipers. An alternative is that internal adipose tissue may be negligible compared with subcutaneous fat, again providing some justification for the use of calipers. If, however, it is not negligible and if there is not a significant relation between internal and subcutaneous adipose tissue masses, then there cannot be an evidence based prediction of total or whole-body adiposity, nor is there a justification to use caliper measurements. Assumption VI - Internal versus external (subcutaneous) adipose tissue equality. In the continuation of reasoning as in assumption V, the Brussels CAS project provides comprehensive data on the relation of internal or visceral to external or

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subcutaneous adipose tissue masses. Fig. 8 shows the mass of dissected adipose tissue for both men and women. These data clearly indicate a high correlation between internal and external masses in women and no correlation in men. Many studies have already indicated that skinfold formulae are sample specific, but here we show that there is no justification for applying skinfold formulae for the prediction of adiposity in men.

36

Figure 8. The relation between internal (visceral + intra muscular) and external (subcutaneous) adipose tissue in men and women.

4. Closing remarks These data suggest clearly that all assumptions in the step-by-step transformation from skinfold measurement to whole-body adiposity are non-existent or highly variable. The assumptions have become very questionable. These problems will result in a serious increase of error with an increasing number of skinfolds within a prediction equation. It is unreasonable to continue to introduce further error into the prediction or determination of total body adiposity by transforming and combining anthropometric (skinfold) values, especially within formulae. On the positive side, it was possible to indicate a few skinfold sites as rather good "indicators" of adiposity. Eventually a summation of subcutaneous adipose tissue sites selected from all storage levels will allow for the prediction of the wholebody adipose tissue status in women (but certainly not in men). These findings have implications for measurements of body composition in health-care workers (see Part III).

References Clarys, J. P., Martin, A. D. and Drinkwater, D. T. (1987). The skinfold: myth and reality. Journal of Sports Sciences, 5, 3-33. Clarys, J. P., Martin, A. D., Marfell-Jones, M. J., Janssens, V., Caboor, D. and Drinkwater, D. T. (1999). Human body composition: a review of adult dissection data. American Journal of Human Biology, 11, 167-174.


Clarys, J. P. and Marfell-Jones, M. J. (1986). Anthropometric prediction of component tissue masses in the minor limb segments of the human body. Human Biology, 58, 761-769. Clarys, J. P., Martin, A. D. and Drinkwater, D. T. (1984). Gross tissue masses in adult humans: data from 25 dissections. Human Biology, 56, 459-73. Clarys, J. P., Martin A. D. and Drinkwater, D. T. (1988). Physical and structural distribution of human skin. Humanbiologia Budapestinensis, 18, 55-63. Duquet, W. (1980). Studie van de toepasbaarheid van de Heath-Carter somatotype methode op kinderen van 6 tot J3jaar. PhD thesis, Vrije Universiteit Brussel. Edwards, D. A. W. (1951). Differences in the distribution of subcutaneous fat with sex and maturity. Clinical Science, 10, 305-15. Garn, S. M. (1955). Relative fat patterning: an individual characteristic. Human Biology, 27, 75-89. Garn, S. M. (1971). Measurement and interpretation of subcutaneous fat, with norms for children and young adult males. British Journal of Preventive Social Medicine, 9, 201-11. Hagar, A. (1981). Estimation of body fat in infants, children and adolescents. In: Adipose Tissue in Childhood (ed. by P. Bonnet), pp. 49-56. Boca Raton, FL: CRC Press. Heath, B. H. and Carter, J. E. L. (1967). A modified somatotype method. American Journal of Physical Anthropology, 27, 57-74. Janssens, V., Thys, P., Clarys, J.P., Kvist, H., Chowdhury, B. and Zinzen, E. (1994). Post-mortem limitations of body composition analysis by computed tomography. Ergonomics, 37, 207-216 Lohman, T. G. (1981). Skinfolds and body density and their relationship to body fatness: a review. Human Biology, 53, 181-225 Martin, A. D. (1984). An anatomical basis for assessing human body composition: evidence from 25 dissections. PhD thesis, Simon Fraser University, Burnaby, Canada (and Vrije Universiteit Brussel). Martin, A. D., Ross, W. D., Drinkwater, D. T. and Clarys, J. P. (1985). Prediction of body fat by skinfold caliper: assumptions and cadaver evidence. International Journal of Obesity, 9, Suppl. 1, 31-9 Mueller, W. H. (1985). Biology of human fat patterning. Communication at the Euro-Nut Conference. London: Ciba Foundation. Mueller, W. H. and Stallones, L. (1981). Anatomical distribution of subcutaneous fat: skinfold site choice and construction of indices. Human Biology, 53, 321-35. Ross, W. D. and Ward, R. (1984). The O-scale System. Vancouver, Canada: Rosscraft.

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Musculoskeletal Disorders in Health-Related Occupations T. Reilfy (Ed.) IOS Press, 2002

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BODY COMPOSITION: PART III In vivo application of a selection of formulae for predicting whole-body adipose tissue in male and female nurses J. P. Clarys, K. Alewaeters and E. Zinzen Department of Experimental Anatomy Vrije Universiteit Brussel Belgium

Abstract: The body's distribution of its adipose tissue is an indication of health among professionals. The aim in this study was to examine the existing equations for predicting body composition from skinfold measurements. Fifty one formulae were investigated. Except for one formula, there was a high correlation between the formulae examined. The simplest method of discriminating adipose tissue difference between subjects is by means of summed skinfolds.

1. Introduction The distribution of the body's adipose tissue mass is an important indicator of health risk. The relationship of its distribution with mortality and disease is well known. Central adipose predominance is a strong risk factor for cardiovascular disease, hypertension, stroke and diabetes. Knowledge of these phenomena is important for the health of the population at large, but in particular for professions known or recognised as "at risk". The nursing profession is one of these, especially in relation to low-back problems (LBP) and musculoskeletal inconveniences. However, against expectations in a study of 784 nurses, no relation was found between skinfold predictions of the whole-body adiposity and LBP associated phenomena (Zinzen, 1998; Zinzen et a/., 2000); assuming the data collection and the corresponding calculations are correct the no-relation status remains. Nevertheless, the calculated predictions confirm what is suggested from cadaver studies (see the two preceeding chapters). The purpose of this part of the study was to select amongst 98 known, anmropometric "whole-body adipose tissue" prediction equations, those formulae that are composed of skinfolds only (=51). Out of these 51 formulae, those equations were chosen that used one or more of the eight (8) skinfolds that were part of the Amsterdam, Brussels, Liverpool "LBP and nurses project" (Fig. 1). This joint venture was

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registered in Belgian and European contracts (BmH4-CT96-1057, PBO98/24-65/85, ST/03/029, HH/03/004).

2. Methods The subscapular skinfold was measured in parallel with the M. latissimus dorsi, 2 cm below the angulus caudalis scapulae; the triceps skinfold was measured at the proximal one third of the upper arm; the biceps skinfold on top of the most visual part of the muscle belly; the abdominal skinfold to the right of the umbilicus; the supra-cliacal (or waist) skinfold was taken 5 cm above SIAS; the thigh skinfold in the frontal mid and the calf skinfold at the medial site of the greatest calf circumference. The thoracic skinfold was measured halfway between the nipple and the umbilicus.

Figure 1. Skinfold distribution in various body segments used in the LBP-nurses project (Zinzen 1998).

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165

This final selection resulted in four (4) suitable formulae for the female nurses and nine (9) equations for the male nursing personnel (Table 1 and 2). Table 1. A selection of formulae for the in vivo estimation of the whole-body adipose tissue in female subjects, using selected skinfolds solely.

Parizkova

1961

1.079-0.043 log X,

Nagamine & Suzuki

1964

1.0869-0.00268 X,

Katch & McArdle

1973

1.08347 + 0.0006 X2 - 0.00151 X, - 0.00097 X6

Parizkova & Roth

1971

40.249 log (X2 + X,)- 32.413

Table 2. A selection of formulae for the in vivo estimation of the whole-body adipose tissue in male subjects, using selected skinfolds solely.

Sloan

1967

1.1043 - 0.00133 X6 - 0.00131 X,

Sloan

1967

1 .0967 - 0.00 1 2 1 X4 - 0.00 1 28 X2

Wilmore & Behnke

1969

1.081 1-0.00195X 2

Wilmore & Behnke

1969

1 .0854 - 0.00086 X4 - 0.0004 X6

Forsyth & Sinning

1973

1.10647 - 0.00162 X, - 0.00144 X4- 0.00077 X2 + 0.0007 1 X8

Katch & McArdle

1973

1.0967 - 0.00103 X2 - 0.00056 X, - 0.00054 X,

Pollock et al.

1976

1.0936 -0.001 86X 2

Lohman

1981

1.0982 - 0.000815 (X2 + X4 + X,) + 0.0000084 (X2 + X4 + X,)2

Parizkova & Roth

1971

33.852 log (X2 + XO- 23.876

These formulae were calculated with the data from 176 males and 608 females (total N - 784). A few of these equations produce a density (D) value in g.cc"1. In those cases the conversion formula of Brozek et al. (1963) - Adipose Tissue = 4.570/D-4.142 - was used in completion. In addition the sums of respectively 3, 6 and 8 skinfolds were added for comparison. This grouping was based on the predictive value for adipose tissue according to the cadaver study (see part II) e.g. the best 3, the best 6, and so on. Table 3 and 4 include their mean, SD, minimum and maximum values.

166

J. P. Clarys et al /Body Composition: Part III

Table 3. Sum of skinfolds (in mm) of male subjects.

3 skinfolds (X) 6 skinfolds (Y) all 8 skinfolds (Z)

Mean 33.69 72.78 86.44

SD 15.13 31.87 36.28

Minimum 10.20 22.60 29.80

Maximum 87.80 188.80 199.50

Skinfolds used: subscapulary'z; tricepsy'z; biceps7; abdominaly>z; supra iliacax'z; thigh x>y>z ; medial calf1*3 thoracicy'z

Table 4. Sum of skinfolds (in mm) of female subjects.

3 skinfolds (X) 6 skinfolds (Y) all 8 skinfolds (Z)

Mean 62.96 112.63 125.98

SD 22.87 42.64 45.15

Minimum 14.20 33.80 41.10

Maximum 177.50 334.20 352.20

Skinfolds used: subscapulary> z; tricepsy'z; bicepsz; abdominal*z; supra iliacax'z; thigh"'y'z; medial calf0 thoracicy'z

3. Results and discussion All formulae are predictors of the "whole-body adipose tissue" both in women and in men. The formulae use the same populations of nursing personnel with their respective skinfolds but the amount of skinfolds used per equation varies. All calculated results correlated almost perfectly, with r between 0.71 and 0.99 (p0.90 in females. The correlation matrix of the males showed a minimum r of 0.76 against a maximum r of = 0.98. One formula showed no correlation at all, namely the Lohman (1981) equation. On this basis, it is acceptable to assume almost equal calculations of the wholebody adipose tissue for all formulae abstracted. This statement is true irrespective of whether it is an overrated, a correct or an underrated value. The female nurses showed a minor variation of maximal value 4% (min. 25% and max. 29% of adipose tissue) between the respectively calculated equations (Fig. 2) while the male nurses had 13% adipose tissue calculated with the equation of Katch and McArdle (1973) against 22% adipose tissue using the formulae of Pariskova and Roth (1971) (Fig. 3). All other calculated values lie in between the previous ones (the data obtained from Lohman are no longer included).

J. P. Clarys et al. / Body Composition: Part III

167

% adipose tissue 35 T

30

25

20 -

15

10

5

Katch & McArdle (73)

Nagamine & Suzuki ('64)

Parizkova ('61)

Parizkova & Roth (71)

Figure 2. The whole-body adipose tissue predictions for female nurses (N=608).

% adipose tissue 35,00 30,00 25,00 20,00 15,00 10,00

5,00 0,00

Forsyth & Sinning

Katch & McArdle

('73)

('73)

Lohman ('81)

Parizkova & Pollock et al. Sloan ('67) Sloan ('67) Roth ('71) ('76)

Wilmore & Behnke

Wilmore & Behnke

('69)

('69)

Figure 3. The whole-body adipose tissue predictions for male nurses (N=176).

168

J.P. Clarys etal. /Body Composition: Part II

We clearly observed greater differences and a higher variation in the male predictions. These data confirm in a sense the findings of the step-by-step cadaver analyses (Part II) and they are enforced by the fact that we measure significantly less skin in the skinfold (see Part I). Observing the male adipose tissue percentages, one might as well visually determine the amount of adipose tissue without really making a greater error than with the prediction equations. This assumption may be bold, but is not unrealistic. The simplest and probably best method to discriminate adipose tissue between subjects e.g. nurses in this case, may be the sum of skinfolds. Realising we used the better predictors first, it clearly makes no difference if one uses the sum of 3, 6 or 8 skinfolds. The discrimination value is close to being equal. Finally, Fig. 4 indicates also that female nurses had a significantly (p

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