Fundamentals of Biomechanics 2nd Edition PDF

Fundamentals of Biomechanics Duane Knudson Fundamentals of Biomechanics Second Edition Duane Knudson Department of Kinesiology California State University at Chico First & Normal Street Chico, CA 95929-0330 USA [email protected] Library of Congress Control Number: 2007925371 ISBN 978-0-387-...

Fundamentals of Biomechanics Duane Knudson Fundamentals of Biomechanics Second Edition Duane Knudson Department of Kinesiology California State University at Chico First & Normal Street Chico, CA 95929-0330 USA [email protected] Library of Congress Control Number: 2007925371 ISBN 978-0-387-49311-4 e-ISBN 978-0-387-49312-1 Printed on acid-free paper. © 2007 Springer Science+Business Media, LLC All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. 9 8 7 6 5 4 3 2 1 springer.com  Contents Preface ix NINE FUNDAMENTALS OF BIOMECHANICS 29 Principles and Laws 29 Acknowledgments xi Nine Principles for Application of Biomechanics 30 QUALITATIVE ANALYSIS 35 PART I SUMMARY 36 INTRODUCTION REVIEW QUESTIONS 36 CHAPTER 1 KEY TERMS 37 INTRODUCTION TO BIOMECHANICS SUGGESTED READING 37 OF HUMAN MOVEMENT WEB LINKS 37 WHAT IS BIOMECHANICS? 3 PART II WHY STUDY BIOMECHANICS? 5 Improving Performance 5 BIOLOGICAL/STRUCTURAL BASES Preventing and Treating Injury 9 Qualitative and Quantitative Analysis 11 CHAPTER 3 WHERE CAN I FIND OUT ABOUT ANATOMICAL DESCRIPTION AND BIOMECHANICS? 12 ITS LIMITATIONS Scholarly Societies 13 Computer Searches 14 REVIEW OF KEY ANATOMICAL CONCEPTS 41 Biomechanics Textbooks 15 Directional Terms 42 BIOMECHANICAL KNOWLEDGE VERSUS Joint Motions 43 INFORMATION 16 Review of Muscle Structure 46 Kinds of Sources 16 MUSCLE ACTIONS 49 Evaluating Sources 18 Active and Passive Tension of Muscle 51 A Word About Right and Hill Muscle Model 51 Wrong Answers 19 THE LIMITATIONS OF FUNCTIONAL SUMMARY 20 ANATOMICAL ANALYSIS 53 REVIEW QUESTIONS 21 Mechanical Method of Muscle Action Analysis 53 KEY TERMS 21 The Need for Biomechanics to SUGGESTED READING 21 Understand Muscle Actions 56 Sports Medicine and Rehabilitation WEB LINKS 22 Applications 60 RANGE-OF-MOTION PRINCIPLE 60 FORCE–MOTION PRINCIPLE 63 CHAPTER 2 SUMMARY 65 FUNDAMENTALS OF BIOMECHANICS AND QUALITATIVE ANALYSIS REVIEW QUESTIONS 66 KEY TERMS 66 KEY MECHANICAL CONCEPTS 23 SUGGESTED READING 66 Mechanics 23 Basic Units 25 WEB LINKS 67 v VI FUNDAMENTALS OF BIOMECHANICS CHAPTER 4 OPTIMAL PROJECTION PRINCIPLE 117 MECHANICS OF THE ANGULAR MOTION 121 MUSCULOSKELETAL SYSTEM Angular Velocity 122 TISSUE LOADS 69 Angular Acceleration 123 RESPONSE OF TISSUES TO FORCES 69 COORDINATION CONTINUUM PRINCIPLE 128 Stress 70 SUMMARY 130 Strain 70 REVIEW QUESTIONS 130 Stiffness and Mechanical Strength 71 Viscoelasticity 72 KEY TERMS 131 BIOMECHANICS OF THE PASSIVE SUGGESTED READING 131 MUSCLE–TENDON UNIT (MTU) 75 WEB LINKS 132 BIOMECHANICS OF BONE 76 BIOMECHANICS OF LIGAMENTS 77 THREE MECHANICAL CHARACTERISTICS CHAPTER 6 OF MUSCLE 79 LINEAR KINETICS Force–Velocity Relationship 79 Force–Length Relationship 84 LAWS OF KINETICS 133 Force–Time Relationship 86 NEWTON'S LAWS OF MOTION 133 STRETCH-SHORTENING CYCLE (SSC) 88 Newton's First Law and First FORCE–TIME PRINCIPLE 92 Impressions 133 Newton's Second Law 136 NEUROMUSCULAR CONTROL 94 Newton's Third Law 137 The Functional Unit of Control: INERTIA PRINCIPLE 139 Motor Units 94 Regulation of Muscle Force 95 MUSCLE ANGLE OF PULL: Proprioception of Muscle Action QUALITATIVE AND QUANTITATIVE and Movement 99 ANALYSIS OF VECTORS 141 SUMMARY 100 Qualitative Vector Analysis of Muscle Angle of Pull 141 REVIEW QUESTIONS 101 Quantitative Vector Analysis of Muscle Angle of Pull 143 KEY TERMS 101 CONTACT FORCES 145 SUGGESTED READING 102 IMPULSE–MOMENTUM RELATIONSHIP 147 WEB LINKS 103 FORCE–TIME PRINCIPLE 149 WORK–ENERGY RELATIONSHIP 151 PART III Mechanical Energy 151 Mechanical Work 155 MECHANICAL BASES Mechanical Power 157 SEGMENTAL INTERACTION PRINCIPLE 160 CHAPTER 5 SUMMARY 164 LINEAR AND ANGULAR KINEMATICS REVIEW QUESTIONS 165 LINEAR MOTION 107 KEY TERMS 166 Speed and Velocity 109 SUGGESTED READING 166 Acceleration 113 Uniformly Accelerated Motion 115 WEB LINKS 167  CONTENTS VII CHAPTER 7 SUMMARY 224 ANGULAR KINETICS DISCUSSION QUESTIONS 224 TORQUE 169 SUGGESTED READING 224 SUMMING TORQUES 173 WEB LINKS 225 ANGULAR INERTIA (MOMENT OF INERTIA) 174 NEWTON'S ANGULAR ANALOGUES 178 CHAPTER 10 EQUILIBRIUM 179 APPLYING BIOMECHANICS IN CENTER OF GRAVITY 180 COACHING PRINCIPLE OF BALANCE 183 QUALITATIVE ANALYSIS OF SUMMARY 189 THROWING TECHNIQUE 227 REVIEW QUESTIONS 190 QUALITATIVE ANALYSIS OF KEY TERMS 190 DRIBBLING TECHNIQUE 228 SUGGESTED READING 191 QUALITATIVE ANALYSIS OF WEB LINKS 191 CONDITIONING 230 RECRUITMENT 231 QUALITATIVE ANALYSIS OF CATCHING 233 CHAPTER 8 SUMMARY 234 FLUID MECHANICS DISCUSSION QUESTIONS 234 FLUIDS 193 SUGGESTED READING 234 FLUID FORCES 193 WEB LINKS 235 Buoyancy 193 Drag 195 Lift 200 CHAPTER 11 The Magnus Effect 203 PRINCIPLE OF SPIN 208 APPLYING BIOMECHANICS IN STRENGTH AND CONDITIONING SUMMARY 210 KEY TERMS 210 QUALITATIVE ANALYSIS OF REVIEW QUESTIONS 210 SQUAT TECHNIQUE 237 SUGGESTED READING 210 QUALITATIVE ANALYSIS OF DROP JUMPS 239 WEB LINKS 211 EXERCISE SPECIFICITY 240 INJURY RISK 242 PART IV EQUIPMENT 244 APPLICATIONS OF BIOMECHANICS SUMMARY 244 IN QUALITATIVE ANALYSIS DISCUSSION QUESTIONS 245 CHAPTER 9 SUGGESTED READING 246 APPLYING BIOMECHANICS IN WEB LINKS 246 PHYSICAL EDUCATION QUALITATIVE ANALYSIS OF KICKING CHAPTER 12 TECHNIQUE 215 QUALITATIVE ANALYSIS OF BATTING 218 APPLYING BIOMECHANICS IN SPORTS MEDICINE AND REHABILITATION QUALITATIVE ANALYSIS OF THE BASKETBALL FREE THROW 219 INJURY MECHANISMS 247 EXERCISE/ACTIVITY PRESCRIPTION 220 EXERCISE SPECIFICITY 248 QUALITATIVE ANALYSIS OF CATCHING 222 EQUIPMENT 250 VIII FUNDAMENTALS OF BIOMECHANICS READINESS 251 LAB ACTIVITIES INJURY PREVENTION 252 1 FINDING BIOMECHANICAL SOURCES L-2 SUMMARY 253 2 QUALITATIVE AND QUANTITATIVE DISCUSSION QUESTIONS 254 ANALYSIS OF RANGE OF MOTION L-4 SUGGESTED READING 254 3 FUNCTIONAL ANATOMY? L-6 WEB LINKS 255 4 MUSCLE ACTIONS AND THE STRETCH- SHORTENING CYCLE (SSC) L-8 REFERENCES 257 5A VELOCITY IN SPRINTING L-10 APPENDIX A 5B ACCURACY OF THROWING GLOSSARY 283 SPEED MEASUREMENTS L-12 APPENDIX B 6A TOP GUN KINETICS: FORCE–MOTION PRINCIPLE L–14 CONVERSION FACTORS 297 6B IMPULSE–MOMENTUM: APPENDIX C FORCE–TIME PRINCIPLE L-16 SUGGESTED ANSWERS TO SELECTED 7A ANGULAR KINETICS OF EXERCISE L-18 REVIEW QUESTIONS 299 7B CALCULATING CENTER OF GRAVITY APPENDIX D USING ANGULAR KINETICS L-20 RIGHT-ANGLE TRIGONOMETRY REVIEW 305 8 MAGNUS EFFECT IN BASEBALL PITCHING L-22 APPENDIX E 9 QUALITATIVE ANALYSIS OF QUALITATIVE ANALYSIS OF LEAD-UP ACTIVITIES L-24 BIOMECHANICAL PRINCIPLES 307 10 COMPARISON OF SKILLED AND NOVICE PERFORMANCE L-26 INDEX 309 11 COMPARISON OF TRAINING MODES L-28 12 QUALITATIVE ANALYSIS OF WALKING GAIT L-30  Preface This second edition of Fundamentals of Lawson & McDermott, 1987; Kim & Pak, Biomechanics was developed primarily to 2002). update a well-received text. The unique- So why another textbook on the biome- ness of integrating biological and mechani- chanics of human motion? There are plenty cal bases in analyzing and improving hu- of books that are really anatomy books man movement has been expanded with with superficial mechanics, that teach me- more examples, figures, and lab activities. chanics with sport examples, or are sport Citations to the latest research and web books that use some mechanics to illustrate links help students access primary sources. technique points. Unfortunately, there are Students and instructors will appreciate the not many books that truly integrate the bi- CD with lab activities, answers to review ological and mechanical foundations of hu- questions, sample questions, and graphics man movement and show students how to files of the illustrations. apply and integrate biomechanical knowl- This book is written for students taking edge in improving human movement. This the introductory biomechanics course in book was written to address these limita- Kinesiology/HPERD. The book is designed tions in previous biomechanics texts. The for majors preparing for all kinds of human text presents a clear conceptual under- movement professions and therefore uses a standing of biomechanics and builds nine wide variety of movement examples to il- principles for the application of biomechan- lustrate the application of biomechanics. ics. These nine principles form the applied While this approach to the application of biomechanics tools kinesiology profession- biomechanics is critical, it is also important als need. The application of these biome- that students be introduced to the scientific chanical principles is illustrated in qualita- support or lack of support for these qualita- tive analysis of a variety of human move- tive judgments. Throughout the text exten- ments in several contexts for the kinesiolo- sive citations are provided to support the gy professional: physical education, coach- principles developed and give students ref- ing, strength and conditioning, and sports erences for further study. Algebraic level medicine. This qualitative analysis ap- mathematics is used to teach mechanical proach meets the NASPE Guidelines and concepts. The focus of the mathematical ex- Standards (Kinesiology Academy, 1992) for amples is to understand the mechanical an introductory biomechanics course, and variables and to highlight the relationship clearly shows students how biomechanical between various biomechanical variables, knowledge must be applied when kinesiol- rather than to solve quantitative biome- ogy professionals improve human move- chanical word problems. It is obvious from ment. research in physics instruction that solving The text is subdivided into four parts: quantitative word problems does not in- Introduction, Biological/Structural Bases, crease the conceptual understanding of im- Mechanical Bases, and Applications of portant mechanical laws (Elby, 2001; Biomechanics in Qualitative Analysis. Each ix X FUNDAMENTALS OF BIOMECHANICS part opener provides a concise summary of of how the biomechanical principles can be the importance and content of that section qualitatively applied to improve human of text. The text builds from familiar ana- movement in a variety of professions. No tomical knowledge, to new biomechanical other text provides as many or as thorough principles and their application. guided examples of applying biomechani- This book has several features that are cal principles in actual human movement designed to help students link personal ex- situations. These application chapters also perience to biomechanical concepts and provide discussion questions so that students that illustrate the application of biome- and instructors can extend the discussion chanics principles. First, nine general prin- and debate on professional practice using ciples of biomechanics are proposed and specific examples. developed throughout the text. These prin- There are also features that make it easy ciples are the application link for the bio- for students to follow the material and mechanical concepts used to improve study for examinations. Extensive use of movement or reduce injury risk. Some texts graphs, photographs, and illustrations are have application chapters at the end of the incorporated throughout. Aside from visual book, but an application approach and ex- appeal, these figures illustrate important amples are built in throughout Funda- points and relationships between biome- mentals of Biomechanics. Second, there are chanical variables and performance. The activity boxes that provide opportunities for book provides an extensive glossary of key students to see and feel the biomechanical terms and biomechanics research terminolo- variables discussed. Third, there are practi- gy so that students can read original biome- cal application boxes that highlight the appli- chanical research. Each chapter provides a cations of biomechanics in improving summary, extensive citations of important movement and in treating and preventing biomechanical research, and suggested read- injury. Fourth, the interdisciplinary issues ings. The chapters in Parts I, II, and III con- boxes show how biomechanics is integrated clude with review questions for student study with other sport sciences in addressing hu- and review. The lists of web links offer stu- man movement problems. Fifth, all chap- dents the internet addresses of significant ters have associated lab activities (located at websites and professional organizations. the end of the book, after the index) that use I hope that you master the fundamen- simple movements and measurements to tals of biomechanics, integrate biomechan- explore concepts and principles. These lab ics into your professional practice, and are activities do not require expensive lab challenged to continuously update your equipment, large blocks of time, or dedicat- biomechanical toolbox. Some of you will ed lab space. Finally, Part IV (chapters 9 find advanced study and a career in biome- through 12) provides real-life case studies chanics exciting opportunities.  Acknowledgments The author would like to thank the many Knutson for many fine illustrations, and people who have contributed to the second Aaron Johnson of Springer for his vision to edition of this book. I am indebted to many make this book happen. biomechanics colleagues who have shared To the ones I truly love—Lois, Josh, their expertise with me, given permission and Mandy—thanks for being such great to share their work, and contributed so people and for sharing the computer. much to students and our profession. I Finally, I would like to thank God for knit- would like to thank Tim Oliver for his ex- ting all of us so “fearfully and wonderfully pert editing, formatting, design, and art ed- made.” iting of the book, Katherine Hanley- xi  PART I INTRODUCTION Kinesiology is the scholarly study of human movement, and biomechanics is one of the many academic subdisciplines of kinesiol- ogy. Biomechanics in kinesiology involves the precise description of human movement and the study of the causes of human move- ment. The study of biomechanics is relevant to professional practice in many kinesiology professions. The physical educator or coach who is teaching movement technique and the athletic trainer or physical therapist treating an injury use biomechanics to quali- tatively analyze movement. The chapters in part I demonstrate the importance of biome- chanics in kinesiology and introduce you to key biomechanical terms and principles that will be developed throughout the text. The lab activities associated with part I relate to finding biomechanical knowledge and iden- tifying biomechanical principles in action. 1  CHAPTER 1 Introduction to Biomechanics of Human Movement Most people are extremely skilled in many WHAT IS BIOMECHANICS? everyday movements like standing, walk- ing, or climbing stairs. By the time children Biomechanics has been defined as the study are two, they are skilled walkers with little of the movement of living things using the sci- instruction from parents aside from emo- ence of mechanics (Hatze, 1974). Mechanics is tional encouragement. Unfortunately, mod- a branch of physics that is concerned with ern living does not require enough move- the description of motion and how forces ment to prevent several chronic diseases create motion. Forces acting on living associated with low physical activity (USD- things can create motion, be a healthy stim- HHS, 1996). Fortunately, many human ulus for growth and development, or over- movement professions help people to par- load tissues, causing injury. Biomechanics ticipate in beneficial physical activities. provides conceptual and mathematical Physical Educators, coaches, athletic train- tools that are necessary for understanding ers, strength & conditioning coaches, per- how living things move and how kinesiol- sonal trainers, and physical therapists all ogy professionals might improve move- help people reap the benefits of physical ac- ment or make movement safer. tivity. These human movement professions Most readers of this book will be ma- rely on undergraduate training in kinesiol- jors in departments of Kinesiology, Human ogy, and typically require coursework in Performance, or HPERD (Health, Physical biomechanics. Kinesiology is the term re- Education, Recreation, and Dance). Kinesi- ferring to the whole scholarly area of hu- ology comes from two Greek verbs that man movement study, while biomechanics translated literally means “the study of is the study of motion and its causes in liv- movement.” Most American higher educa- ing things. Biomechanics provides key in- tion programs in HPERD now use “kinesi- formation on the most effective and safest ology” in the title of their department be- movement patterns, equipment, and rele- cause this term has come to be known as vant exercises to improve human move- the academic area for the study of human ment. In a sense, kinesiology professionals movement (Corbin & Eckert, 1990). This solve human movement problems every change in terminology can be confusing be- day, and one of their most important tools cause “kinesiology” is also the title of a is biomechanics. This chapter outlines the foundational course on applied anatomy field of biomechanics, why biomechanics is that was commonly required for a physical such an important area to the kinesiology education degree in the first half of the professional, and where biomechanics in- twentieth century. This older meaning of formation can be found. kinesiology persists even today, possibly 3 4 FUNDAMENTALS OF BIOMECHANICS because biomechanics has only recently many sport and human movement science (since 1970s) become a recognized special- tools in a kinesiology professional's tool- ization of scientific study (Atwater, 1980; box. This text is also based on the philoso- Wilkerson, 1997). phy that your biomechanical tools must be This book will use the term kinesiology combined with tools from other kinesiology in the modern sense of the whole academic sciences to most effectively deal with hu- area of the study of human movement. man movement problems. Figure 1.1a illus- Since kinesiology majors are pursuing ca- trates the typical scientific subdisciplines of reers focused on improving human move- kinesiology. These typically are the core sci- ment, you and almost all kinesiology stu- ences all kinesiology majors take in their dents are required to take at least one undergraduate preparations. This overview course on the biomechanics of human should not be interpreted to diminish the movement. It is a good thing that you are other academic subdisciplines common in studying biomechanics. Once your friends kinesiology departments like sport history, and family know you are a kinesiology ma- sport philosophy, dance, and sport admin- jor, you will invariably be asked questions istration/management, just to name a few. like: should I get one of those new rackets, The important point is that knowledge why does my elbow hurt, or how can I stop from all the subdisciplines must be inte- my drive from slicing? Does it sometimes grated in professional practice since prob- seem as if your friends and family have re- lems in human movement are multifaceted, gressed to that preschool age when every with many interrelated factors. For the other word out of their mouth is “why”? most part, the human movement problems What is truly important about this common you face as a kinesiology professional will experience is that it is a metaphor for the be like those “trick” questions professors life of a human movement professional. ask on exams: they are complicated by Professions require formal study of theoret- many factors and tend to defy simple, dual- ical and specialized knowledge that allows istic (black/white) answers. While the ap- for the reliable solution to problems. This is plication examples discussed in this text the traditional meaning of the word “pro- will emphasize biomechanical principles, fessional,” and it is different than its com- readers should bear in mind that this bio- mon use today. Today people refer to pro- mechanical knowledge should be inte- fessional athletes or painters because grated with professional experience and the people earn a living with these jobs, but I other subdisciplines of kinesiology. It is this believe that kinesiology careers should interdisciplinary approach (Figure 1.1b) strive to be more like true professions such that is essential to finding the best interven- as medicine or law. tions to help people more effectively and People need help in improving human safely. Dotson (1980) suggests that true ki- movement and this help requires knowl- nesiology professionals can integrate the edge of “why” and “how” the human body many factors that interact to affect move- moves. Since biomechanics gives the kine- ment, while the layman typically looks at siology professional much of the knowl- things one factor at time. Unfortunately, edge and many of the skills necessary to an- this interdisciplinary approach to kinesiol- swer these “what works?” and “why?” ogy instruction in higher education has questions, biomechanics is an important been elusive (Harris, 1993). Let's look at science for solving human movement prob- some examples of human movement prob- lems. However, biomechanics is but one of lems where it is particularly important to  CHAPTER 1: INTRODUCTION TO BIOMECHANICS OF HUMAN MOVEMENT 5 Figure 1.1. (a) The major academic subdisciplines or sciences of kinesiology. (b) Schematic of the integration of all the sciences in an interdisciplinary approach to solving human movement problems in kinesiology. integrate biomechanical knowledge into movement can be classified into two main the qualitative analysis. areas: the improvement of performance and the reduction or treatment of injury (Figure 1.2). WHY STUDY BIOMECHANICS? Scientists from many different areas (e.g., Improving Performance kinesiology, engineering, physics, biology, zoology) are interested in biomechanics. Human movement performance can be en- Why are scholars from so many different hanced many ways. Effective movement academic backgrounds interested in animal involves anatomical factors, neuromuscu- movement? Biomechanics is interesting be- lar skills, physiological capacities, and psy- cause many people marvel at the ability chological/cognitive abilities. Most kinesi- and beauty in animal movement. Some ology professionals prescribe technique scholars have purely theoretical or aca- changes and give instructions that allow a demic interests in discovering the laws person to improve performance. Biome- and principles that govern animal move- chanics is most useful in improving per- ment. Within kinesiology, many biomech- formance in sports or activities where tech- anists have been interested in the applica- nique is the dominant factor rather than tion of biomechanics to sport and exercise. physical structure or physiological capac- The applications of biomechanics to human ity. Since biomechanics is essentially the 6 FUNDAMENTALS OF BIOMECHANICS body arch are performed poorly. The coach's experience tells him that this athlete is strong enough to perform this skill, but they must decide if the gymnast should concentrate on her takeoff angle or more back hyperextension in the block. The coach uses his knowledge of biomechanics to help in the qualitative analysis of this sit- uation. Since the coach knows that a better arch affects the force the gymnast creates against the mat and affects the angle of takeoff of the gymnast, he decides to help the gymnast work on her “arch” following the round off. Biomechanics research on sports tech- niques sometimes tends to lag behind the changes that are naturally occurring in sports. Athletes and coaches experiment with new techniques all the time. Students of biomechanics may be surprised to find that there are often limited biomechanical Figure 1.2. The two major applications of biomechan- ics are to improve human movement and the treat- ment or prevention of injury. science of movement technique, biome- chanics is the main contributor to one of the most important skills of kinesiology profes- sionals: the qualitative analysis of human movement (Knudson & Morrison, 2002). Imagine a coach is working with a gymnast who is having problems with her Figure 1.3. Biomechanics principles must be inte- back handspring (Figure 1.3). The coach ob- grated with other kinesiology sciences to solve human serves several attempts and judges that the movement problems, like in the qualitative analysis a angle of takeoff from the round off and round off and back handspring.  CHAPTER 1: INTRODUCTION TO BIOMECHANICS OF HUMAN MOVEMENT 7 studies on many techniques in many popu- ing designs. When these changes are lar sports. The vast number of techniques, integrated with information about the their variations, and their high rates of human performer, we can say the improve- change and innovation tend to outdistance ments in equipment were based on biome- biomechanics research resources. Sport bio- chanics. Engineers interested in sports mechanics research also lags behind the equipment often belong to the Intern- coaches and athletes because scientific re- ational Sports Engineering Association search takes considerable time to conduct (http://www.sportsengineering.org/) and and report, and there is a lack of funding publish research in ISEA proceedings for this important research. There is less (Subic & Haake, 2000) or the Sports Engi- funding for biomechanical studies aimed at neering journal. Research on all kinds of improving performance compared to stud- equipment is conducted in biomechanics ies focused on preventing and treating in- labs at most major sporting goods manu- juries. Students looking for biomechanical facturers. Unfortunately, much of the re- research on improving sports technique of- sults of these studies are closely guarded ten will have fewer sources than students trade secrets, and it is difficult for the researching the biomechanics of injury. layperson to determine if marketing claims While technique is always relevant in for “improvements” in equipment design human movement, in some activities the are real biomechanical innovations or just psychological, anatomical, or physiological creative marketing. factors are more strongly related to success. There are many examples of how ap- Running is a good example of this kind of plying biomechanics in changing equip- movement. There is a considerable amount ment designs has improved sports per- of research on the biomechanics of running formance. When improved javelin designs so coaches can fine tune a runner's tech- in the early 1980s resulted in longer throws nique to match the profile of elite runners that endangered other athletes and specta- (Cavanagh, Andrew, Kram, Rogers, San- tors, redesigns in the weight distribution of derson, & Hennig, 1985; Buckalew, Barlow, the “new rules” javelin again shortened Fischer, & Richards, 1985; Williams, Ca- throws to safer distances (Hubbard & Al- vanagh, & Ziff, 1987). While these tech- aways, 1987). Biomechanics researchers (El- nique adjustments make small improve- liott, 1981; Ward & Groppel, 1980) were ments in performance, most of running some of the first to call for smaller tennis performance is related to physiological rackets that more closely matched the mus- abilities and their training. Studies that pro- cular strength of young players (Figure 1.4). vide technique changes in running based Chapter 8 will discuss how changes in on biomechanical measurements have sports equipment are used to change fluid found minimal effects on running economy forces and improve performance. (Cavanagh, 1990; Lake & Cavanagh, 1996; While breaking world records using Messier & Cirillo, 1989). This suggests that new equipment is exciting, not all changes track coaches can use biomechanics to re- in equipment are welcomed with open fine running technique, but they should arms by sport governing bodies. Some only expect small changes in performance equipment changes are so drastic they from these modifications. change the very nature of the game and are Human performance can also be en- quickly outlawed by the rules committee of hanced by improvements in the design of the sport. One biomechanist developed a equipment. Many of these improvements way to measure the stiffness of basketball are related to new materials and engineer- goals, hoping to improve the consistency of 8 FUNDAMENTALS OF BIOMECHANICS of the engineers than athletes (Bjerklie, 1993). Another way biomechanics research improves performance is advances in exer- cise and conditioning programs. Bio- mechanical studies of exercise movements and training devices serve to determine the most effective training to improve perform- ance (Figure 1.5). Biomechanical research on exercises is often compared to research on the sport or activity that is the focus of training. Strength and conditioning profes- sionals can better apply the principle of specificity when biomechanical research is used in the development of exercise pro- grams. Computer-controlled exercise and testing machines are another example of how biomechanics contributes to strength and conditioning (Ariel, 1983). In the next section the application of biomechanics in the medical areas of orthotics and prosthet- ics will be mentioned in relation to prevent- ing injury, but many prosthetics are now Figure 1.4. The design of sports equipment must be being designed to improve the performance appropriate for an athlete, so rackets for children are of disabled athletes. shorter and lighter than adult rackets. Photo used with permission from Getty Images. their response but found considerable re- sistance from basketball folks who liked their unique home court advantages. An- other biomechanist recently developed a new “klap” speed skate that increased the time and range of motion of each push off the ice, dramatically improving times and breaking world records (de Koning, Hou- dijk, de Groot, & Bobbert, 2000). This gave quite an advantage to the country where these skates were developed, and there was controversy over the amount of time other skaters were able to practice with the new skates before competition. These dramatic Figure 1.5. A computerized testing and exercise dy- equipment improvements in many sports namometer by Biodex. The speed, muscle actions (iso- metric, concentric, eccentric), and pattern of loading have some people worried that winning (isokinetic, isotonic) can be selected. Image courtesy of Olympic medals may be more in the hands Biodex Medical Systems.  CHAPTER 1: INTRODUCTION TO BIOMECHANICS OF HUMAN MOVEMENT 9 Preventing and Treating Injury amputation, prosthetics or artificial limbs can be designed to match the mechanical Movement safety, or injury prevention/ properties of the missing limb (Klute treatment, is another primary area where Kallfelz, & Czerniecki, 2001). Preventing biomechanics can be applied. Sports medi- acute injuries is also another area of biome- cine professionals have traditionally stud- chanics research. Forensic biomechanics in- ied injury data to try to determine the volves reconstructing the likely causes of potential causes of disease or injury (epi- injury from accident measurements and demiology). Biomechanical research is a witness testimony. powerful ally in the sports medicine quest Biomechanics helps the physical thera- to prevent and treat injury. Biomechanical pist prescribe rehabilitative exercises, assis- studies help prevent injuries by providing tive devices, or orthotics. Orthotics are information on the mechanical properties support objects/braces that correct defor- of tissues, mechanical loadings during mities or joint positioning, while assistive movement, and preventative or rehabilita- devices are large tools to help patient func- tive therapies. Biomechanical studies pro- tion like canes or walkers. Qualitative vide important data to confirm potential in- analysis of gait (walking) also helps the jury mechanisms hypothesized by sports therapist decide whether sufficient muscu- medicine physicians and epidemiological lar strength and control have been regained studies. The increased participation of girls in order to permit safe or cosmetically nor- and women in sports has made it clear that mal walking (Figure 1.6). An athletic trainer females are at a higher risk for anterior cru- might observe the walking pattern for ciate ligament (ACL) injuries than males signs of pain and/or limited range of mo- due to several biomechanical factors (Bo- tion in an athlete undergoing long-term den, Griffin, & Garrett, 2000). Continued conditioning for future return to the field. biomechanical and sports medicine studies An athletic coach might use a similar quali- may help unravel the mystery of this high risk and develop prevention strategies (see Chapter 12). Engineers and occupational therapists use biomechanics to design work tasks and assistive equipment to prevent overuse in- juries related to specific jobs. Combining biomechanics with other sport sciences has aided in the design of shoes for specific sports (Segesser & Pforringer, 1989), espe- cially running shoes (Frederick, 1986; Nigg, 1986). Since the 1980s the design and engi- neering of most sports shoes has included research in company biomechanics labs. The biomechanical study of auto accidents has resulted in measures of the severity of head injuries, which has been applied in biomechanical testing, and in design of many kinds of helmets to prevent head in- Figure 1.6. Qualitative analysis of gait (walking) is of jury (Calvano & Berger, 1979; Norman, importance in physical therapy and the treatment of 1983; Torg, 1992). When accidents result in many musculoskeletal conditions. 10 FUNDAMENTALS OF BIOMECHANICS tative analysis of the warm-up activities of the same athlete several weeks later to judge their readiness for practice or compe- tition. Many biomechanists work in hospi- tals providing quantitative assessments of gait function to document the effectiveness of therapy. The North American group in- terested in these quantitative assessments for medical purposes is the Gait and Clini- cal Movement Analysis Society (GCMAS) at http://www.gcmas.net/cms/index.php. Good sources for the clinical and biome- chanical aspects of gait are Kirtley (2006), Perry (1992), Whittle (1996), and the clini- cal gait analysis website: http://guardian. Figure 1.7. Biomechanical measurements and soft- ware can be used to make accurate animations of hu- curtin.edu.au/cga/. man motion that can be used for technique improve- Dramatic increases in computer mem- ment, cinema special effects, and computer games. ory and power have opened up new areas Drawing based on image provided by Vicon Motion of application for biomechanists. Many of Systems. these areas are related to treating and pre- venting human injury. Biomechanical stud- ies are able to evaluate strategies for pre- that computer game animations have the venting falls and fractures in the elderly look of truly human movement, but with (Robinovitch, Hsiao, Sandler, Cortez, Liu, & the superhuman speed that makes games Paiement, 2000). Biomechanical computer exciting (Figure 1.7). Some people use bio- models can be used to simulate the effect of mechanics to perform forensic examina- various orthopaedic surgeries (Delp, Loan, tions. This reconstruction of events from Hoy, Zajac, & Rosen, 1990) or to educate physical measurements at the scene is com- with computer animation. Some biomech- bined with medical and other evidence to anists have developed software used to determine the likely cause of many kinds of adapt human movement kinematic data so accidents. Application A variety of professions are interested in using biomechanics to modify human movement.A person that fabricates prosthetics (artificial limbs) would use biomechanics to understand the normal functioning of joints, the loadings the prosthetic must withstand, and how the prosthetic can be safely attached to the person. List possible questions biomechanics could answer for a(n): Athletic Coach? Orthopaedic Surgeon? Physical Educator? Physical Therapist? Athletic Trainer? Strength & Conditioning Professional? Occupational Fitness Consultant? You? What question about human movement technique are you curious about?  CHAPTER 1: INTRODUCTION TO BIOMECHANICS OF HUMAN MOVEMENT 11 Qualitative and Quantitative and processing time, as well as dangers of Analysis increasing errors with the additional com- putations involved. Even with very fast Biomechanics provides information for a modern computers, quantitative biome- variety of kinesiology professions to ana- chanics is a labor-intensive task requiring lyze human movement to improve effec- considerable graduate training and experi- tiveness or decrease the risk of injury. How ence. For these reasons and others, qualita- the movement is analyzed falls on a contin- tive analysis of human movement remains uum between a qualitative analysis and a the main approach kinesiology profession- quantitative analysis. Quantitative analy- als use in solving most human movement sis involves the measurement of biome- problems. Qualitative analysis will be the chanical variables and usually requires a main focus of the applications of biome- computer to do the voluminous numerical chanics presented in this book. Whether calculations performed. Even short move- your future jobs use qualitative or quantita- ments will have thousands of samples of tive biomechanical analysis, you will need data to be collected, scaled, and numeri- to be able to access biomechanical knowl- cally processed. In contrast, qualitative edge. The next section will show you many analysis has been defined as the “system- sources of biomechanical knowledge. atic observation and introspective judg- ment of the quality of human movement for the purpose of providing the most appro- Activity:Videotape Replay priate intervention to improve perform- ance” (Knudson & Morrison, 2002, p. 4). Tape a sporting event from a TV broadcast on a VCR. Find a sequence in the video where Analysis in both quantitative and qualita- there is a movement of interest to you and tive contexts means identification of the where there is a good close-up shot of the ac- factors that affect human movement per- tion.You could also video yourself performing formance, which is then interpreted using a movement using a camcorder.Watch the re- other higher levels of thinking (synthesis, play at real-time speed and try to estimate evaluation) in applying the information to the percentage of time taken up by the major the movement of interest. Solving problems phases of the movement. Most skills can be in human movement involves high levels of broken down into three phases—prepara- critical thinking and an interdisciplinary tion, action, and follow-through—but you can approach, integrating the many kinesiology have as many phases as you think apply to the sciences. movement of interest. Rewind the tape and The advantages of numerical measure- use the “pause” and “frame” advance func- ments of quantitative over those of qualita- tions to count the number of video frames in tive analysis are greater accuracy, consis- the skill and calculate the times and percent- tency, and precision. Most quantitative ages for each phase of the skill. Most VCRs biomechanical analysis is performed in re- show every other field, giving you a video search settings; however, more and more “clock” with 30 pictures per second. Note, however, that some VCRs show you every devices are commercially available that in- field (half of interlaced video) so your clock expensively measure some biomechanical will be accurate to 1/60th of a second. How variables (e.g., radar, timing lights, timing could you check what your or the classes' mats, quantitative videography systems). VCR does in frame advance mode? How Unfortunately, the greater accuracy of close was your qualitative judgment to the quantitative measures comes at the cost of more accurate quantitative measure of time? technical skills, calibration, computational 12 FUNDAMENTALS OF BIOMECHANICS Application Even though qualitative and quantitative analyses are not mutually exclusive, assume that qual- itative-versus-quantitative biomechanical analysis is an either/or proposition in the following exercise. For the sports medicine and athletics career areas, discuss with other students what kind of analysis is most appropriate for the questions listed. Come to a consensus and be pre- pared to give your reasons (cost, time, accuracy, need, etc.) for believing that one approach might be better than another. Sport Medicine 1. Is the patient doing the lunge exercise correctly? 2. Is athlete “A” ready to play following rehab for their injured ACL? Athletics 1. Should pole vaulter “B” change to a longer pole? 2. Is athlete “A” ready to play following rehab for their injured ACL? WHERE CAN I FIND OUT have made adaptations to be good at cer- ABOUT BIOMECHANICS? tain kinds of movements: like fish, kanga- roos, or frogs. Much of this biomechanical This text provides a general introduction to research on animals is relevant to the study the biomechanics of human movement in of human movement. kinesiology. Many students take advanced Professionals from many fields are in- courses in biomechanics and do library re- terested in human movement, so there is search for term projects. This text will pro- considerable interest and research in hu- vide quite a few references on many topics man biomechanics. As a science biome- that will help students find original sources chanics is quite young (infant), but biome- of biomechanical data. The relative youth of chanics is more like the middle child within the science of biomechanics and the many the subdisciplines of kinesiology. Biome- different academic areas interested in bio- chanics is not as mature as Exercise Physiol- mechanics (among others, biology, engi- ogy or Motor Learning but is a bit older neering, medicine, kinesiology, physics) than Sport Psychology and other subdisci- makes the search for biomechanical knowl- plines. Basic biomechanics research on edge challenging for many students. This many popular sport techniques will have section will give you a brief tour of some of been conducted in the early to mid-20th the major fields where biomechanics re- century. Biomechanics research in kinesiol- search is of interest. ogy since the 1970s has tended to become Where you find biomechanics research more narrowly focused and specialized, depends on the kind of data you are inter- and has branched into areas far beyond ested in. Many people are curious about sport and education. As a result, students human movement, but there are also many with basic sport technique interests now scholars who are interested in the biome- have to integrate biomechanics research chanics of a wide variety of animals. An ex- over a 50-year period. cellent way to study the theoretical aspects Depending on the depth of analysis of biomechanics is to study animals that and the human movement of interest, a stu-  CHAPTER 1: INTRODUCTION TO BIOMECHANICS OF HUMAN MOVEMENT 13 dent of biomechanics may find himself planted in humans, the majority of the in- reading literature in biomechanical, med- vasive research to determine the actions of ical, physiological, engineering, or other muscles in movement is done on animals specialized journals. The smaller and more (Figure 1.8). narrow the area of biomechanical interest (for example, specific fibers, myofibrils, ligaments, tendons), the more likely there Scholarly Societies will be very recent research on the topic. Research on the effect of computerized re- There are scholarly organizations exclu- tail check-out scanners would likely be sively dedicated to biomechanics. Scholarly found in recent journals related to engineer- societies typically sponsor meetings and ing, human factors, and ergonomics. A stu- publications to promote the development dent interested in a strength and condition- of their fields. Students of sport biome- ing career might find biomechanical studies chanics should know that the International on exercises in medical, physical education, Society of Biomechanics in Sports (ISBS) is physiology, and specialized strength and devoted to promotion of sport biomechan- conditioning journals. Students with clini- ics research and to helping coaches apply cal career interests who want to know ex- biomechanical knowledge in instruction, actly what muscles do during movement training, and conditioning for sports. The may put together data from studies dealing ISBS publishes scholarly papers on sports with a variety of animals. Clues can come biomechanics that are accepted from papers from classic research on the muscles of the presented at their annual meetings and the frog (Hill, 1970), the cat (Gregor & Abelew, journal Sports Biomechanics. Their website 1994) and turkeys (Roberts, Marsh, (http://isbs.org/) provides links to a vari- Weyand, & Taylor, 1997), as well as human ety of information on sport biomechanics. muscle (Ito, Kawakami, Ichinose, Fuka- The websites for the societies discussed in shiro, & Fukunaga, 1998). While muscle this section are listed at the end of this force-measuring devices have been im- chapter and in a file on the CD. Figure 1.8. Schematic of a buckle transducer for in vivo measurement of muscle forces in animal locomotion. Adapted with permission from Biewener and Blickhan (1988). 14 FUNDAMENTALS OF BIOMECHANICS The International Society of Biome- the biomechanics interest group (BIG). chanics (ISB) is the international society of Other professional organizations in medi- scholars interested in biomechanics from all cine, physical therapy, athletic training, kinds of academic fields. The ISB hosts in- and/or strength and conditioning sponsor ternational meetings and sponsors journals. biomechanics programs related to their Some examples of regional biomechanics unique interests. Whatever career path you societies include the American Society of select, it is important that you join and par- Biomechanics (ASB), the Canadian Society ticipate in the related scholarly and profes- of Biomechanics, and the European Soci- sional organizations. ety of Biomechanics. The ASB website has several links, including a list of graduate programs and papers accepted for presen- tation at ABS annual meetings. Another re- Computer Searches lated scholarly society is the International Society for Electrophysiology and Kinesiol- One of the best ways to find information on ogy (ISEK), which promotes the elec- human biomechanics is to use computer- tromyographic (EMG) study of human ized bibliographies or databases of books, movement. Engineers interested in equip- chapters, and articles. Some of the best elec- ment design, sport, and human movement tronic sources for kinesiology students are have founded the ISEA mentioned earlier. SportDiscus, MEDLINE, and EMBASE. There are other scholarly organizations that SportDiscus is the CD-ROM version of the have biomechanics interest groups related database compiled by the Sport Infor- to the parent disciplines of medicine, biol- mation Resource Center (SIRC) in Ontario, ogy, or physics. Canada (http://www.sirc.ca/). SIRC has Aside from the many specialized bio- been compiling scholarly sources on sport mechanics societies, there are biomechanics and exercise science since 1973. Many uni- interest groups in various scholarly/pro- versities buy access to SportDiscus and Med- fessional organizations that have an interest line for faculty and student research. Sport- in human movement. Two examples are Discus is quite helpful in locating research the American Alliance for Health, Physical papers in the ISBS edited proceedings. Education, Recreation, and Dance (AAH- Medical literature has been well cata- PERD) and the American College of Sports loged by Index Medicus and the searchable Medicine (ACSM). AAHPERD is the origi- databases MEDLINE and EMBASE. These nal physical education scholarly/profes- databases are quite extensive but do not list sional organization, founded in 1885. Bio- all published articles so a search of both is mechanists in HPERD can be active in the advisable (Minozzi, Pistotti, & Forni, 2000) Biomechanics Academy of the National As- for literature searches related to sports sociation for Sport and Physical Education medicine. Besides access from your univer- (NASPE is one of the HPERD associations sity library, the national library of medicine within the alliance). The American College provides free searching of Medline at of Sports Medicine was founded in 1954 by http://www.ncbi.nlm.nih.gov/entrez/ physicians and exercise scientists to be a query.fcgi. Very large databases like Sport- scholarly society interested in promotion of Discus, Medline, and EMBASE are great re- the study and application of exercise, sports search tools if searched intelligently. These medicine, and sports science. The ACSM databases and others (e.g., Biological Ab- substructure interested in biomechanics is stracts, Science Citation Index) should be  CHAPTER 1: INTRODUCTION TO BIOMECHANICS OF HUMAN MOVEMENT 15 searched by the careful linking of keywords biomechanics. The President's Council on and Boolean (logic: and, or) operators. Re- Physical Fitness and Sports publishes Phys- member that much of the power of index- ical Fitness/Sports Medicine. The Physical Ed- ing is the cross-referencing as well as the di- ucation Index is a bibliographic service for rect listings for your search items. English language publications that is pub- Many journals now publish keywords lished quarterly by BenOak Publishing. with articles to facilitate the searching for The PE Index reviews more than 170 maga- the articles with similar terms. The search zines and journals, provides some citations request for “biomechanics” in some data- from popular press magazines, and this in- bases will return all items (probably too dex can be used to gather “common knowl- many) beginning with these letters in the ti- edge.” Early sport and exercise biomechan- tle, abstract, or keywords including biome- ics research has been compiled in several chanics or biomechanical. Searching for bibliographies published by the University “kinematic and ankle” will find sources of Iowa (Hay, 1987). documenting the motion at the ankle joint. Even better would be “kinematic or ankle or subtalar,” because any one of the three search terms matching would select a re- Biomechanics Textbooks source. You miss very little with this search, but it is necessary to go through quite a Good sources for knowledge and links (not few sources to find the most relevant ones. hyperlinks) to sources commonly missed Be persistent in your search and let your by students are biomechanics textbooks. readings refine your search strategy. A stu- Biomechanics students should look up sev- dent interested in occupational overuse in- eral biomechanics textbooks and review juries (sports medicine term) will find that their coverage of a research topic. Scholars the human factors field may refer to this often write textbooks with research inter- topic as “cumulative trauma disorder,” ests that are blended into their texts, and “work-related musculoskeletal disorders,” many authors make an effort to provide ex- or “occupational overuse syndrome” just to tensive reference lists for students. Remem- name a few (Grieco, Molteni, DeVito, & ber that writing books takes considerable Sias, 1998). time, so references in a particular text may There are bibliographies of literature not be totally up-to-date, but they do give that are in print that list sources relevant to students leads and clues on many good Interdisciplinary Issue: Collaborative Biomechanics Finding biomechanics information is like a scavenger hunt that will lead students all over a li- brary.We have seen that biomechanics research can be found in biology, engineering, medical, and other specialized journals. “Interdisciplinary” means using several different disciplines si- multaneously to solve a problem. Do some preliminary research for sources (journals and ed- ited proceedings/books) on a human movement of interest to you. Do the titles and abstracts of the sources you found suggest scholars from different disciplines are working together to solve problems, or are scholars working on a problem primarily from their own area or dis- cipline? What have other students found in their research? 16 FUNDAMENTALS OF BIOMECHANICS sources. The quality of a biomechanical known and rise to the level of scientific law. source will be difficult for many students to While most biomechanical knowledge is judge, so the next section will coach you in not perfect and can only be organized into evaluating biomechanical sources. some general principles, it is much better at guiding professional practice than merely using information or trail and error. Living in an information age, it is easy BIOMECHANICAL KNOWLEDGE for people to become insensitive to the im- VERSUS INFORMATION portant distinction between information and knowledge. The most important differ- Knowledge is different from information. ence is that information has a much higher Knowledge is contextual, theory-based, chance of being incorrect than knowledge. and data-supported ideas that make the Information is merely access to opinions or best current explanation for reality. Scien- data, with no implied degree of accuracy. tific knowledge is a theoretical structure of Information is also much easier to access in laws and principles that is built on the con- the age of the Internet and wireless commu- sensus of experimental evidence by scien- nications. Do not confuse ease of access tists in that field. Students often fail to real- with accuracy or value. This distinction is ize that knowledge is a structure that is clearer as you look at the hierarchy of the constantly being constructed and remod- kinds of sources used for scholarly research eled as new theories and evidence are ex- and a simple strategy for the evaluation of amined, and transitions in the structure are the quality of a source. often controversial. Biomechanical knowledge is built by a Kinds of Sources consensus of scientists from a variety of dis- ciplines interested in human movement When searching for specific biomechanical (e.g., biology, engineering, kinesiology, knowledge it is important to keep in mind medicine). Most real-world human move- the kind of source you are reading. There is ment problems have only partial answers a definite hierarchy of the scholarly or aca- because of limited biomechanical research demic rigor of published research and writ- or knowledge that is specifically related to ing. Figure 1.9 illustrates typical examples the context of the person and problem of in- of this hierarchy. Although there are excep- terest. Although the stack of biomechanical tions to most rules, it is generally true that knowledge is not perfect, a critical review the higher up a source on the hierarchy the of this will be the best guide and closest to better the chance that the information pre- the truth. sented is closer to the current state of The modification of human movement knowledge and the truth. For this reason based on biomechanical knowledge is diffi- professionals and scholars focus their atten- cult because movement is a multifaceted tion on peer-reviewed journals to maintain problem, with many factors related to the a knowledge base for practice. Some pub- performer and activity all interacting to af- lishers are now “publishing” electronic ver- fect the outcome. The next chapter will sions of their journals on the world wide present nine general principles of biome- web (WWW) for subscribers or make pa- chanical knowledge that are useful in ap- pers available for free after a certain wait- plying biomechanics in general to improve ing period. human movement. There will be a few bits Most scholarly journals publish origi- of the knowledge puzzle that are well nal research that extends the body of  CHAPTER 1: INTRODUCTION TO BIOMECHANICS OF HUMAN MOVEMENT 17 Figure 1.9. The many kinds of biomechanics sources of information and the hierarchy of their academic rigor. knowledge, or review papers that attempt cusing on. Reading biomechanics research to summarize a body of knowledge. Many will be challenging for most undergradu- journals also publish supplements that con- ates. Appendix A provides a comprehen- tain abstracts (short summaries of a re- sive glossary of biomechanics terms that search study) of papers that have been ac- will help you when reading the biomechan- cepted for presentation at a scholarly ics literature related to your professional in- meeting or were published in another jour- terests. nal. While the review of these abstracts is In the middle of academic rigor are ed- not as rigorous as a full journal article, ab- ited proceedings, edited books, and profes- stracts do provide students with clues sional journals. These publications have about what the most recent research is fo- varying degrees of peer review before pub- 18 FUNDAMENTALS OF BIOMECHANICS lication, as well as varying rules on what internet (WWW) involves profit and self- constitutes acceptable evidence. At the bot- promotion based on numbers of viewers tom of the credibility chain are popular and, therefore, is more prone to sensational- press publications (magazines/newspa- ize and to not weigh all the evidence. pers) and hypertext on the worldwide web. The “e” in the acronym stands for the While these sources are appropriate for key element of all science: evidence. Science more subjective observations of laypersons, is based on logical analysis and the balance there are serious threats to the validity of of many controlled studies. This weighing the observations from these sources. The of all the evidence stands in stark contrast major problems with webpages are their to the more emotional claims of the popular impermanence (unlike archival research lit- press. The more emotional and sensational erature) and the lack of review (anyone can the language, even if it talks about “the lat- post a webpage). Another good example est study,” the more likely you are reading is the teaching and coaching tips pub- only part of the whole picture. Remember lished by the Physical Education Digest that the structure of knowledge is a compli- (http://www.pedigest.com). Most of tips cated structure built over time using many and cues are opinions of coaches and teach- small pieces. The “latest” piece of the ers in popular press magazines that have knowledge puzzle may be in error (see the not been tested by scientific research. It is next section) or will be rejected by most possible that some of these opinions are scholars as having flaws that make it less correct and useful, but there is little evi- valuable as other research. dence used to verify the advice, so kinesiol- This simple “me” strategy is just the ogy professionals should verify with other first step in learning more professional primary sources before using the advice. strategies for weighing evidence. In medi- The next section will summarize a quick cine and allied health there are formal method for checking the credibility of vari- methods for classifying the strength of sci- ous sources for biomechanical knowledge. entific evidence called “evidence-based practice” to assist in diagnosis and treat- ment (Hadorn et al., 1996; Sackett et al., Evaluating Sources 1996). Authors have called the sports medi- The previous section clearly suggests that cine and kinesiology professions to more certain sources and kinds of evidence are consistently focus on using critical review more likely to be accurate. When evaluat- of evidence to support practice (Faulkner et ing the credibility of sources that fall at sim- al., 2006; Knudson, 2005; Shrier, 2006). ilar levels of rigor, the “me” test can be eas- One formidable barrier to a kinesiology ily applied to judge the chance of the advice professional's ability to weigh biomechani- being a good and balanced representation cal evidence is the technical and specialized of reality. The “m” stands for motivation. terminology employed in most studies. What is the motivation for the person or Throughout this text many of these meas- source providing the information? Sources urement systems and mechanical terms are with little financial interest in to making the covered. Appendix A provides an extensive observations/claims and who are dedi- glossary of biomechanical terms and quan- cated to advancing a body of knowledge or titative measurement systems. Two papers human potential (scholarly journals) are that provide good summaries of biome- much more likely to provide accurate infor- chanical and exercise science terms are mation. The motivation of the popular available (Knuttgen & Kraemer, 1987; press (TV, newspapers, magazines) and the Rogers & Cavanagh, 1984). Students re-  CHAPTER 1: INTRODUCTION TO BIOMECHANICS OF HUMAN MOVEMENT 19 Application On your next trip to a physician or other medical professional's waiting room, evaluate the nature of the articles and advertisements in the magazines and displays you encounter. Do ad- vertisements related to claims in the articles appear near the article? Do the articles talk about several studies, their relative merits, as well as the percentage of subjects with various responses? Does the professional you are visiting sell supplements or products to patients? If so, what does this tell you about motivation and potential conflicts of interest between prac- tice and profits? The biomechanics of most health and human performance problems in hu- man movement are classic examples of complicated problems, with many interrelated factors and variability in the response of individuals to treatment. viewing biomechanical studies should ask these everyday questions/problems do not their instructor for assistance when the text have easy, dichotomous (right/wrong) an- or these sources do not clear up their un- swers. There are many factors that affect derstanding. most phenomena and there is variation in nearly all phenomena. In fact, all true sci- ence is written using statistics to account for this variation. Statistics use estimates of A Word About Right and data variation to attach a probability to any Wrong Answers yes/no decision about the data. If you read a study that says an observation was signif- The increasing amount and complexity of icant at the 0.05 level, this only means that research and technology tends to give the result is not likely a fluke or observation many people a false sense of the correctness due to chance variation alone. It is possible of numbers. Few people will question a that chance alone created this “difference,” measurement if some machine output num- and p < 0.05 means that in the long run bers on a printout, unless they are very fa- there is about a 1-in-20 chance that the ob- miliar with the measurement. Like our servation or decision about the data is knowledge-versus-information discussion, wrong. Since most studies use this error it is very important for kinesiology profes- standard (p < 0.05), this means that, out of sionals to understand that the process of re- twenty studies on a particular topic, one viewing and weighing the evidence is often likely reports an incorrect observation from more important than finding the perfect or chance variation alone. A common miscon- “right” answer. Such absolutes in a compli- ception among laypersons is that statistics cated world are quite rare, usually only oc- in a scientific study “proves” things. Statis- curring when a technique change would tics only provide tools that allow scientists run against a law of physics or one of our to place probability values about yes/no principles of biomechanics. These princi- decisions on the numbers observed in their ples (and laws) of mechanics are the appli- research. Proof is a long-term process re- cation tools developed throughout this quiring critical review of the whole body of book. research on the issue. Remember this when So the good news is that biomechanics television news broadcasts sensationalize helps kinesiology professionals solve prob- the results of the “latest” study on some lems, while the bad news is that most of health issue or you are tempted to believe 20 FUNDAMENTALS OF BIOMECHANICS access biomechanical knowledge, and the other Interdisciplinary Issue: is the critical thinking necessary to evaluate Too Much Performance? and integrate knowledge so it can be ap- plied in solving human movement prob- Recent controversies about sport per- lems. You are not likely going to remember formance enhancement through steroids everything in this book (though you would and genetics parallel the issues related to be wise to), but you should have the knowl- biomechanics and improvements in equip- edge to access, and critical thinking tools ment. Engineers and biomechanists have that allow you to find, evaluate, and apply used advances in technology to improve biomechanics to human movement. The the materials and design of sports equip- rest of this text will illustrate and explicate ment, although the use of tools in sport the nine principles of biomechanics, which has a long history (Minetti, 2004). Jenkins are tools you would do well to never forget (2004) presents a nice review of how im- when helping people improve their move- provements in equipment materials has ment. dramatically affected performance in sev- eral sports. These are truly interdiscipli- nary controversies because there are eth- SUMMARY ical, safety, athlete, coaching, and sport/his- torical perspectives on performance. One example of technology correcting too Kinesiology is the scholarly study of hu- much performance is the new rules for man movement. A core science in the aca- the javelin in the mid-1980s.The center of demic discipline of kinesiology is biome- gravity of the the javelin was moved for- chanics. Biomechanics in kinesiology is the ward to decrease throwing distances be- study of motion and its causes in human cause many athletes were throwing the movement. The field of biomechanics is rel- old javelin over 100 m.Advances in biome- atively new and only has a few principles chanics and computer technologies have and laws that can be used to inform profes- also been used to modify technique, train- sional practice. Kinesiology professionals ing, and equipment for the Olympics often use biomechanical knowledge in the (Legwold, 1984; Sheppard, 2006). qualitative analysis of human movement to decide on how to intervene to improve movement and prevent or remediate injury. Applying biomechanics in qualitative that one biomechanical study settles a par- analysis is most effective when a profes- ticular issue. sional integrates biomechanical knowledge Biomechanical knowledge is constantly with professional experience and the other changing and usually cannot be easily clas- subdisciplines of kinesiology. Biomechani- sified into always right or wrong answers, cal knowledge is found in a wide variety of so there are two important professional journals because there are many academic tools you must not forget to use. These tools and professional areas interested in the will work quite well with the biomechani- movement of living things. Students study- cal tools (nine principles) developed in this ing human biomechanics might find rele- text. These two tools are the Swiss Army vant biomechanical knowledge in books Knives™ or Leathermen™ of your profes- and journals in applied physics, biology, sional toolbox because of they are so flexi- engineering, ergonomics, medicine, physi- ble and important. One is your ability to ology, and biomechanics.  CHAPTER 1: INTRODUCTION TO BIOMECHANICS OF HUMAN MOVEMENT 21 REVIEW QUESTIONS SUGGESTED READING 1. What is biomechanics and how is it Bartlett, R. M. (1997). Current issues in the me- different from the two common meanings chanics of athletic activities: A position paper. of kinesiology? Journal of Biomechanics, 30, 477–486. 2. Biomechanical knowledge is useful Cavanagh, P. R. (1990). Biomechanics: A bridge for solving what kinds of problems? builder among the sport sciences. Medicine and 3. What are the advantages and disad- Science in Sports and Exercise. 22, 546–557. vantages of a qualitative biomechanical analysis? Chaffin, D., & Andersson, G. (1991). Occupa- 4. What are the advantages and disad- tional biomechanics (2nd ed.). New York: Wiley. vantages of a quantitative biomechanical Elliott, B. (1999). Biomechanics: An integral analysis? part of sport science and sport medicine. 5. What kinds of journals publish bio- Journal of Science and Medicine and Sport, 2, mechanics research? 299–310. 6. What is the difference between knowledge and information? Knudson, D. V., & Morrison, C. M. (2002). 7. Why should biomechanical knowl- Qualitative analysis of human movement (2nd edge be integrated with other sport and ex- ed.). Champaign, IL: Human Kinetics. ercise sciences in solving human movement Kumar, S. (1999). Biomechanics in ergonomics. problems? London: Taylor & Francis. Lees, A. (1999). Biomechanical assessment of individual sports for improved performance. KEY TERMS Sports Medicine, 28, 299–305. Sheppard, L. M. (2006). Visual effects and biomechanics video analysis lead to Olympics victories. IEEE electromyography (EMG) Computer Graphics and Applications, 26(2), 6–11. information LeVeau, B. (1992). Williams and Lissner's: interdisciplinary Biomechanics of human motion (3rd ed.). kinesiology Philadelphia: W. B. Sanders. knowledge orthotics Segesser, B., & Pforringer, W. (Eds.) (1989). The prosthetics shoe in sport. Chicago: Year Book Medical qualitative analysis Publishers. quantitative analysis Yeadon, M. R., & Challis, J. H. (1994). The future of performance-related sports biome- chanics research. Journal of Sports Sciences, 12, 3–32. 22 FUNDAMENTALS OF BIOMECHANICS WEB LINKS AAHPERD—American Alliance for Health, Physical Education, Recreation, and Dance is the first professional HPERD organization in the United States. http://www.aahperd.org/ Biomechanics Academy—A biomechanics interest area within AAHPERD and NASPE (National Association for Sport and Physical Education). http://www.aahperd.org/naspe/template.cfm?template=specialinterests- biomechanics.html AAKPE—American Academy of Kinesiology and Physical Education is the premier, honorary scholarly society in kinesiology. http://www.aakpe.org/ ACSM—American College of Sports Medicine is a leader in the clinical and scientific aspects of sports medicine and exercise. ACSM provides the leading professional certi- fications in sports medicine. http://acsm.org/ ISB—International Society of Biomechanics was the first biomechanics scholarly society. http://www.isbweb.org/ ASB—American Society of Biomechanics posts meeting abstracts from a variety of bio- mechanical scholars. http://www.asbweb.org/ ISEA—International Sports Engineering Association hosts international meetings and publishes the journal Sports Engineering. http://www.sportsengineering.co.uk/ ISBS—International Society of Biomechanics in Sports hosts annual conferences and indexes papers published in their proceedings and journal (Sports Biomechanics). http://www.isbs.org/ ISEK—International Society of Electrophysiological Kinesiology is the scholarly society focusing on applied electromyography (EMG) and other electrophysiological phenomena. http://isek-online.org/ ISI—The Institute for Scientific Information (Thompson Scientific) provides a variety of services, including rating scholarly journals and authors. http://www.isinet.com/isi/ Medline—Free searching of this medical database provided by the National Library of Medicine. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi/ SIRC—The Sport Information Resource Center provides several database services for sport and kinesiology literature like SportDiscus. Many college libraries have subscrip- tions to SportDiscus. http://www.sirc.ca/  CHAPTER 2 Fundamentals of Biomechanics and Qualitative Analysis In Chapter 1 we found that biomechanics KEY MECHANICAL CONCEPTS provides tools that are needed to analyze human motion, improve performance, and Mechanics reduce the risk of injury. In order to facili- tate the use of these biomechanical tools, Before we can begin to understand how hu- this text will emphasize the qualitative un- mans move, there are several mechanical derstanding of mechanical concepts. Many terms and concepts that must be clarified. chapters, however, will include some quan- Mechanics is the branch of physics that titative examples using the algebraic defi- studies the motion of objects and the forces nitions of the mechanical variables being that cause that motion. The science of me- discussed. Mathematical formulas are a chanics is divided into many areas, but the precise language and are most helpful in three main areas most relevant to biome- showing the importance, interactions, and chanics are: rigid-body, deformable-body, relationships between biomechanical vari- and fluids. ables. While more rigorous calculus forms In rigid-body mechanics, the object be- of these equations provide the most accu- ing analyzed is assumed to be rigid and the rate answers commonly used by scientists deformations in its shape so small they can (Beer & Johnson, 1984; Hamill & Knutzen, be ignored. While this almost never hap- 1995; Zatsiorsky, 1998, 2002), the majority pens in any material, this assumption is of kinesiology majors will benefit most quite reasonable for most biomechanical from a qualitative understanding of these studies of the major segments of the body. mechanical concepts. So this chapter begins The rigid-body assumption in studies saves with key mechanical variables and termi- considerable mathematical and modeling nology essential for introducing other bio- work without great loss of accuracy. Some mechanical concepts. This chapter will em- biomechanists, however, use deformable- phasize the conceptual understanding of body mechanics to study how biological these mechanical variables and leave more materials respond to external forces that detailed development and quantitative ex- are applied to them. Deformable-body me- amples for later in the text. Next, nine gen- chanics studies how forces are distributed eral principles of biomechanics are intro- within a material, and can be focused at duced that will be developed throughout many levels (cellular to tissues/organs/ the rest of the text. These principles use less system) to examine how forces stimulate technical language and are the tools for ap- growth or cause damage. Fluid mechanics plying biomechanical knowledge in the is concerned with the forces in fluids (liq- qualitative analysis of human movement. uids and gasses). A biomechanist would use The chapter concludes by summarizing a fluid mechanics to study heart valves, model of qualitative analysis that is used in swimming, or adapting sports equipment the application section of the book. to minimize air resistance. 23 24 FUNDAMENTALS OF BIOMECHANICS Figure 2.1. The major branches of mechanics used in most biomechanical studies. Most sports biomechanics studies are variables have the adjective “angular” be- based on rigid-body models of the skeletal fore them. Kinetics is concerned with de- system. Rigid-body mechanics is divided termining the causes of motion. Examples into statics and dynamics (Figure 2.1). Sta- of kinetic variables in running are the forces tics is the study of objects at rest or in uni- between the feet and the ground or the form (constant) motion. Dynamics is the forces of air resistance. Understanding study of objects being accelerated by the ac- these variables gives the track coach knowl- tions of forces. Most importantly, dynamics edge of the causes of running performance. is divided into two branches: kinematics Kinetic