The effect of backpack loading configuration and design features on postural stability, energy cost, comfort and shoulder interface pressure

Transcription

1 The effect of backpack loading configuration and design features on postural stability, energy cost, comfort and shoulder interface pressure By Samira Golriz BSc, MSc in Physiotherapy This thesis is presented for the degree of Doctor of Philosophy, Murdoch University 2013 i

2 I declare that this thesis is my own account of my research and contains as its main content work which has not previously been submitted for a degree at any tertiary education institution. Samira Golriz ii

3 Abstract While backpacks are commonly used to transfer extra load, they are sometimes associated with negative effects on the body. The broad aim of this thesis was to study the effect of backpack loading configurations on postural stability, physiological variables, perceived exertion, and interface pressure and compare them to an unloaded condition. The specific aims of this thesis were to: 1) systematically review the literature and identify relevant deficits in knowledge; 2) assess the test-retest reliability and criterion validity of a force plate which has unknown psychometric properties; 3) examine the effect of carrying a 20% of body weight loaded backpack and load placement in a backpack (high vs. low load placement) on postural stability, physiological variables and backpack-shoulder interface pressure; 4) assess the effect of hip belt use on postural stability; and 5) investigate the effect of shoulder strap width on backpack-shoulder interface pressure. These aims were investigated using force plates, a metabolic cart, pressure sensors, and questionnaires. Our results indicated that carrying loaded backpacks decreased postural stability, increased physiological variables and perceived exertion as compared to an unloaded condition. While a hip belt did not enhance postural stability, participants reported a perception of increased stability and less exertion. Load placement did not influence postural stability, physiological variables, perceived stability or exertion; however, participants reported lower levels of local perceived exertion at the shoulders and the upper back regions when the load was placed low in the backpack. Conversely, low load placement resulted in higher shoulder interface pressure as compared to high load placement. Shoulder strap width also affected shoulder interface pressure with wide shoulder straps associated with lower shoulder interface pressure. While we identified several aspects of backpack configuration and loading characteristics and their effects on postural stability, energy cost, interface pressure and perceived exertion, additional study of backpack configuration and the resulting impact on biomechanical and physiologic characteristics is required. iii

4 Acknowledgements I would like to express my deepest gratitude to my supervisors, Dr Bruce Walker and Dr Jeffrey Hebert, for their invaluable understanding, insight, guidance and support which contributed enormously to my success through this long process. Without a doubt, they were there for me, even during the hardest times of my study to be a light, not a judge. I would also like to thank my external supervisor, Dr Bo Foreman, for his advice and assistance throughout my work. I would like to extend my gratitude to Dr Jeremiah Peiffer for his help with a section of this project. Thanks must also go to the staff of School of Chiropractic and Sports Science at Murdoch University. I would like to offer my sincere appreciation to my parents, Simin and Hashem, and my sister, Naghmeh, for their constant support and encouragement in my life. Last but not least, I would like to thank my best friend and husband, Navid, whose love, support, encouragement and patience contributed immensely to the completion of my PhD study, and my son, Kian, who has brought deeper meanings and purposes to my life with his recent arrival. iv

5 TABLE OF CONTENTS Abstract.. iii Acknowledgements iν List of Tables... List of Figures... ix xii Statement of Candidate Contribution. xiv CHAPTER ONE- Introduction 1 Background The broad aim of the thesis 3 Specific aims and hypotheses of this thesis... 3 Overview of the thesis... 5 References CHAPTER TWO- Backpacks. Several factors likely to influence design and usage: A systematic literature review.. 8 Abstract Introduction. 12 Methods Results Discussion References CHAPTER THREE- Can load carriage system weight, design and placement affect pain and discomfort? A systematic review.. 38 v

6 Abstract Introduction. 42 Methods Results Discussion Conclusion.. 59 References CHAPTER FOUR- The reliability of a portable clinical force plate used for the assessment of static postural control: repeated measures reliability study 66 Abstract Introduction. 70 Methods Results Discussion Conclusion References CHAPTER FIVE- The validity of a portable clinical force plate in assessment of static postural control: concurrent validity study 82 Abstract Introduction. 86 Material and methods Results Discussion References vi

7 CHAPTER SIX- The effect of hip belt use and load placement in a backpack on postural stability and perceived exertion: a within subjects trial. 99 Abstract Introduction. 103 Methods Results Discussion References CHAPTER SEVEN- The effect of backpack load placement on physiological and self-reported measures of exertion Abstract Introduction. 126 Methods Results Discussion References CHAPTER EIGHT- The effect of shoulder strap width and load placement on shoulder backpack interface pressure Abstract Introduction. 144 Methods Results Discussion References vii

8 CHAPTER NINE- Conclusion APPENDICES viii

9 LIST OF TABLES Chapter 2 Page Table1 NHMRC level of evidence. 15 Table 2 Table 3 Table 4 Table 5 Table 6 Descriptive characteristics of studies that evaluated the best placement of a backpack on the spine.. Quality appraisal of studies that evaluated the best placement of a backpack on the spine.. Descriptive characteristics of studies which investigated front pack or double pack vs. backpack Critical appraisal of studies which investigated front pack or double pack vs. backpack... Descriptive characteristics of studies that investigated shoulder straps Table 7 Quality appraisal of studies that investigated shoulder straps 27 Table 8 Recommendations for best backpack. 29 Chapter 3 Table 1 NHMRC level of evidence 44 Table 2 Table 3 Table 4 Table 5 Table 6 Descriptive characteristics of the studies that assessed the correlation between backpack use and pain, perceived exertion and discomfort.. Results of the studies that assessed the correlation between backpack use and pain..... Results of the studies that assessed the correlation between backpack use and perceived exertion.. Quality appraisal of studies that assessed the correlation between backpack use and pain Descriptive characteristics of studies that examined the ix

10 effect of load placement on pain 53 Table 7 Table 8 Table 9 Chapter 4 Quality appraisal of studies that examined the effect of load placement on pain Descriptive characteristics of studies that examined if different designs can reduce pain, perceived exertion and discomfort.. Quality appraisal of studies that examined if different designs can reduce the pain Table 1 Reliability results of single measures and means of 2, 3, 4 and 5 measures for each variable 75 Chapter 5 Table 1 Criterion validity analysis.. 92 Chapter 6 Table 1 Demographic and Baseline Characteristics of Participants 110 Table 2 Table 3 Chapter 7 Mean (standard deviation) and mean difference (95% CI) values during unloaded, hip belt and no hip belt condition. Mean (standard deviation) and mean difference (95% CI) values during unloaded, high load placement and low load placement Table 1 Demographic and Baseline Characteristics of Participants 131 Table 2 Chapter 8 Table 1 Table 2 Mean (standard deviation), mean difference (95% CI) values during unloaded, high and low load placement conditions Mean (SD) of peak and average backpack shoulder interface pressure under different width shoulder straps (kpa) and load placements... Mean (SD) of peak and average backpack axilla interface pressure under different width shoulder straps (kpa) and x

11 load placements 149 xi

12 LIST OF FIGURES Chapter 3 Page Figure 1 Inclusion and exclusion of articles. 46 Chapter 4 Figure 1 The Midot Posture Scale Analyser. 72 Chapter 5 Figure 1 The Midot Posture Scale Analyzer and The Accugait AMTI 88 Figure 2 Differences between filtered and unfiltered average velocity vs. cut off frequency to decide the best filter frequency Figure 3 Bland-Altman plot representing comparison of average velocity between the MPSA and the Accugait.. Figure 4 Bland-Altman plot representing comparison of sway area between the MPSA and the Accugait Chapter 6 Figure 1 The Promopak backpack. 108 Figure 2 The loading conditions in the backpack. 108 Figure 3 Perceived exertion of neck, shoulders, upper back, lower back, lower extremity in unloaded, hip belt and no hip belt conditions.. Figure 4 Perceived exertion of neck, shoulders, upper back, lower back and lower extremity in unloaded, high and low load placements Chapter 7 Figure 1 The loading conditions in the backpack 152 Chapter 8 Figure 1 The manikin and position of the pressure sensors Figure 2 The SAS harness backpack 146 Figure 3 Average backpack-shoulder interface pressure under various 150 xii

13 shoulder strap widths in high and low load placement Figure 4 Average backpack-axillary area interface pressure under various shoulder strap widths in high and low load placement xiii

14 Statement of Candidate Contribution The work involved in designing and conducting the studies described in this thesis has been conducted principally by Samira Golriz (the candidate). The thesis, outline and experimental design of the studies was developed and planned by the candidate, in consultation with her supervisors Associate Professor Bruce Walker, Dr Jeffrey Hebert, Dr Bo Foreman. All participant recruitment was carried out by the candidate, along with the implementation and undertaking of data collections. The candidate was responsible for all data analysis and original drafting of all chapters contained within this thesis. The supervisors have provided feedback on all drafts of chapters contained within this thesis. xiv