Biomechanics has been defined as the study of the movement of living things using the science of mechanics (Hatze, 1974). Mechanics is a branch of physics that is concerned with the description of motion and how forces create motion. Forces acting on living things can create motion, be a healthy stimulus for growth and development, or overload tissues, causing injury. Biomechanics provides conceptual and mathematical tools that are necessary for understanding how living things move and how kinesiol-ogy professionals might improve movement or make movement safer.
Most readers of this book will be majors in departments of Kinesiology, Human Performance, or HPERD (Health, Physical Education, Recreation, and Dance). Kinesiology comes from two Greek verbs that translated literally means "the study of movement." Most American higher education programs in HPERD now use "kinesi-ology" in the title of their department because this term has come to be known as the academic area for the study of human movement (Corbin & Eckert, 1990). This change in terminology can be confusing because "kinesiology" is also the title of a foundational course on applied anatomy that was commonly required for a physical education degree in the first half of the twentieth century. This older meaning of kinesiology persists even today, possibly because biomechanics has only recently (since 1970s) become a recognized specialization of scientific study (Atwater, 1980; Wilkerson, 1997).
This book will use the term kinesiology in the modern sense of the whole academic area of the study of human movement. Since kinesiology majors are pursuing careers focused on improving human movement, you and almost all kinesiology students are required to take at least one course on the biomechanics of human movement. It is a good thing that you are studying biomechanics. Once your friends and family know you are a kinesiology major, you will invariably be asked questions like: should I get one of those new rackets, why does my elbow hurt, or how can I stop my drive from slicing? Does it sometimes seem as if your friends and family have regressed to that preschool age when every other word out of their mouth is "why"? What is truly important about this common experience is that it is a metaphor for the life of a human movement professional. Professions require formal study of theoretical and specialized knowledge that allows for the reliable solution to problems. This is the traditional meaning of the word "professional," and it is different than its common use today. Today people refer to professional athletes or painters because people earn a living with these jobs, but I believe that kinesiology careers should strive to be more like true professions such as medicine or law.
People need help in improving human movement and this help requires knowledge of "why" and "how" the human body moves. Since biomechanics gives the kine-siology professional much of the knowledge and many of the skills necessary to answer these "what works?" and "why?" questions, biomechanics is an important science for solving human movement problems. However, biomechanics is but one of many sport and human movement science tools in a kinesiology professional's toolbox. This text is also based on the philosophy that your biomechanical tools must be combined with tools from other kinesiology sciences to most effectively deal with human movement problems. Figure 1.1a illustrates the typical scientific subdisciplines of kinesiology. These typically are the core sciences all kinesiology majors take in their undergraduate preparations. This overview should not be interpreted to diminish the other academic subdisciplines common in kinesiology departments like sport history, sport philosophy, dance, and sport administration/management, just to name a few.
The important point is that knowledge from all the subdisciplines must be integrated in professional practice since problems in human movement are multifaceted, with many interrelated factors. For the most part, the human movement problems you face as a kinesiology professional will be like those "trick" questions professors ask on exams: they are complicated by many factors and tend to defy simple, dual-istic (black/white) answers. While the application examples discussed in this text will emphasize biomechanical principles, readers should bear in mind that this bio-mechanical knowledge should be integrated with professional experience and the other subdisciplines of kinesiology. It is this interdisciplinary approach (Figure 1.1b) that is essential to finding the best interventions to help people more effectively and safely. Dotson (1980) suggests that true ki-nesiology professionals can integrate the many factors that interact to affect movement, while the layman typically looks at things one factor at time. Unfortunately, this interdisciplinary approach to kinesiol-ogy instruction in higher education has been elusive (Harris, 1993). Let's look at some examples of human movement problems where it is particularly important to
integrate biomechanical knowledge into the qualitative analysis.
WHY STUDY BIOMECHANICS?
movement can be classified into two main areas: the improvement of performance and the reduction or treatment of injury (Figure 1.2).
Scientists from many different areas (e.g., kinesiology, engineering, physics, biology, zoology) are interested in biomechanics. Why are scholars from so many different academic backgrounds interested in animal movement? Biomechanics is interesting because many people marvel at the ability and beauty in animal movement. Some scholars have purely theoretical or academic interests in discovering the laws and principles that govern animal movement. Within kinesiology, many biomech-anists have been interested in the application of biomechanics to sport and exercise. The applications of biomechanics to human
Human movement performance can be enhanced many ways. Effective movement involves anatomical factors, neuromuscular skills, physiological capacities, and psychological/cognitive abilities. Most kinesiology professionals prescribe technique changes and give instructions that allow a person to improve performance. Biome-chanics is most useful in improving performance in sports or activities where technique is the dominant factor rather than physical structure or physiological capacity. Since biomechanics is essentially the
Applications of Biomechanics t *
Improved Preventing or
Performance Treating Injury
Improved Preventing or
Performance Treating Injury
science of movement technique, biomechanics is the main contributor to one of the most important skills of kinesiology professionals: the qualitative analysis of human movement (Knudson & Morrison, 2002).
Imagine a coach is working with a gymnast who is having problems with her back handspring (Figure 1.3). The coach observes several attempts and judges that the angle of takeoff from the round off and 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 situation. 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 techniques 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
studies on many techniques in many popular sports. The vast number of techniques, their variations, and their high rates of change and innovation tend to outdistance biomechanics research resources. Sport bio-mechanics research also lags behind the coaches and athletes because scientific research takes considerable time to conduct and report, and there is a lack of funding for this important research. There is less funding for biomechanical studies aimed at improving performance compared to studies focused on preventing and treating injuries. Students looking for biomechanical research on improving sports technique often will have fewer sources than students researching the biomechanics of injury.
While technique is always relevant in human movement, in some activities the psychological, anatomical, or physiological factors are more strongly related to success. Running is a good example of this kind of movement. There is a considerable amount of research on the biomechanics of running so coaches can fine tune a runner's technique to match the profile of elite runners (Cavanagh, Andrew, Kram, Rogers, Sanderson, & Hennig, 1985; Buckalew, Barlow, Fischer, & Richards, 1985; Williams, Ca-vanagh, & Ziff, 1987). While these technique adjustments make small improvements in performance, most of running performance is related to physiological abilities and their training. Studies that provide technique changes in running based on biomechanical measurements have found minimal effects on running economy (Cavanagh, 1990; Lake & Cavanagh, 1996; Messier & Cirillo, 1989). This suggests that track coaches can use biomechanics to refine running technique, but they should only expect small changes in performance from these modifications.
Human performance can also be enhanced by improvements in the design of equipment. Many of these improvements are related to new materials and engineer ing designs. When these changes are integrated with information about the human performer, we can say the improvements in equipment were based on biome-chanics. Engineers interested in sports equipment often belong to the International Sports Engineering Association (http://www.sportsengineering.org/) and publish research in ISEA proceedings (Subic & Haake, 2000) or the Sports Engineering journal. Research on all kinds of equipment is conducted in biomechanics labs at most major sporting goods manufacturers. Unfortunately, much of the results of these studies are closely guarded trade secrets, and it is difficult for the layperson to determine if marketing claims for "improvements" in equipment design are real biomechanical innovations or just creative marketing.
There are many examples of how applying biomechanics in changing equipment designs has improved sports performance. When improved javelin designs in the early 1980s resulted in longer throws that endangered other athletes and spectators, redesigns in the weight distribution of the "new rules" javelin again shortened throws to safer distances (Hubbard & Al-aways, 1987). Biomechanics researchers (Elliott, 1981; Ward & Groppel, 1980) were some of the first to call for smaller tennis rackets that more closely matched the muscular strength of young players (Figure 1.4). Chapter 8 will discuss how changes in sports equipment are used to change fluid forces and improve performance.
While breaking world records using new equipment is exciting, not all changes in equipment are welcomed with open arms by sport governing bodies. Some equipment changes are so drastic they change the very nature of the game and are quickly outlawed by the rules committee of the sport. One biomechanist developed a way to measure the stiffness of basketball goals, hoping to improve the consistency of
their response but found considerable resistance from basketball folks who liked their unique home court advantages. Another 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 equipment improvements in many sports have some people worried that winning Olympic medals may be more in the hands of the engineers than athletes (Bjerklie, 1993).
Another way biomechanics research improves performance is advances in exercise and conditioning programs. Bio-mechanical studies of exercise movements and training devices serve to determine the most effective training to improve performance (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 professionals can better apply the principle of specificity when biomechanical research is used in the development of exercise programs. 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 prosthetics will be mentioned in relation to preventing injury, but many prosthetics are now being designed to improve the performance of disabled athletes.
Preventing and Treating Injury
Movement safety, or injury prevention/ treatment, is another primary area where biomechanics can be applied. Sports medicine professionals have traditionally studied injury data to try to determine the potential causes of disease or injury (epidemiology). Biomechanical research is a powerful ally in the sports medicine quest to prevent and treat injury. Biomechanical studies help prevent injuries by providing information on the mechanical properties of tissues, mechanical loadings during movement, and preventative or rehabilitative therapies. Biomechanical studies provide important data to confirm potential injury mechanisms hypothesized by sports medicine physicians and epidemiological studies. The increased participation of girls and women in sports has made it clear that females are at a higher risk for anterior cruciate ligament (ACL) injuries than males due to several biomechanical factors (Boden, Griffin, & Garrett, 2000). Continued biomechanical and sports medicine studies 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 injuries related to specific jobs. Combining biomechanics with other sport sciences has aided in the design of shoes for specific sports (Segesser & Pforringer, 1989), especially running shoes (Frederick, 1986; Nigg, 1986). Since the 1980s the design and engineering 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 injury (Calvano & Berger, 1979; Norman, 1983; Torg, 1992). When accidents result in amputation, prosthetics or artificial limbs can be designed to match the mechanical properties of the missing limb (Klute Kallfelz, & Czerniecki, 2001). Preventing acute injuries is also another area of biome-chanics research. Forensic biomechanics involves reconstructing the likely causes of injury from accident measurements and witness testimony.
Biomechanics helps the physical therapist prescribe rehabilitative exercises, assis-tive devices, or orthotics. Orthotics are support objects/braces that correct deformities or joint positioning, while assistive devices are large tools to help patient function like canes or walkers. Qualitative analysis of gait (walking) also helps the therapist decide whether sufficient muscular strength and control have been regained in order to permit safe or cosmetically normal walking (Figure 1.6). An athletic trainer might observe the walking pattern for signs of pain and/or limited range of motion in an athlete undergoing long-term conditioning for future return to the field. An athletic coach might use a similar quali-
tative analysis of the warm-up activities of the same athlete several weeks later to judge their readiness for practice or competition. Many biomechanists work in hospitals providing quantitative assessments of gait function to document the effectiveness of therapy. The North American group interested in these quantitative assessments for medical purposes is the Gait and Clinical 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 clinical gait analysis website: http://guardian. curtin.edu.au/cga/.
Dramatic increases in computer memory and power have opened up new areas of application for biomechanists. Many of these areas are related to treating and preventing human injury. Biomechanical studies are able to evaluate strategies for preventing falls and fractures in the elderly (Robinovitch, Hsiao, Sandler, Cortez, Liu, & Paiement, 2000). Biomechanical computer models can be used to simulate the effect of various orthopaedic surgeries (Delp, Loan, Hoy, Zajac, & Rosen, 1990) or to educate with computer animation. Some biomech-anists have developed software used to adapt human movement kinematic data so
that computer game animations have the look of truly human movement, but with the superhuman speed that makes games exciting (Figure 1.7). Some people use bio-mechanics to perform forensic examinations. This reconstruction of events from physical measurements at the scene is combined with medical and other evidence to determine the likely cause of many kinds of accidents.
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?
Biomechanics provides information for a variety of kinesiology professions to analyze human movement to improve effectiveness or decrease the risk of injury. How the movement is analyzed falls on a continuum between a qualitative analysis and a quantitative analysis. Quantitative analysis involves the measurement of biome-chanical variables and usually requires a computer to do the voluminous numerical calculations performed. Even short movements will have thousands of samples of data to be collected, scaled, and numerically processed. In contrast, qualitative analysis has been defined as the "systematic observation and introspective judgment of the quality of human movement for the purpose of providing the most appropriate intervention to improve performance" (Knudson & Morrison, 2002, p. 4). Analysis in both quantitative and qualitative contexts means identification of the factors that affect human movement performance, which is then interpreted using other higher levels of thinking (synthesis, evaluation) in applying the information to the movement of interest. Solving problems in human movement involves high levels of critical thinking and an interdisciplinary approach, integrating the many kinesiology sciences.
The advantages of numerical measurements of quantitative over those of qualitative analysis are greater accuracy, consistency, and precision. Most quantitative biomechanical analysis is performed in research settings; however, more and more devices are commercially available that inexpensively measure some biomechanical variables (e.g., radar, timing lights, timing mats, quantitative videography systems). Unfortunately, the greater accuracy of quantitative measures comes at the cost of technical skills, calibration, computational and processing time, as well as dangers of increasing errors with the additional computations involved. Even with very fast modern computers, quantitative biome-chanics is a labor-intensive task requiring considerable graduate training and experience. For these reasons and others, qualitative analysis of human movement remains the main approach kinesiology professionals use in solving most human movement problems. Qualitative analysis will be the main focus of the applications of biome-chanics presented in this book. Whether your future jobs use qualitative or quantitative biomechanical analysis, you will need to be able to access biomechanical knowledge. The next section will show you many sources of biomechanical knowledge.
Tape a sporting event from a TV broadcast on a VCR. Find a sequence in the video where there is a movement of interest to you and where there is a good close-up shot of the ac-tion.You could also video yourself performing a movement using a camcorder.Watch the replay at real-time speed and try to estimate the percentage of time taken up by the major phases of the movement. Most skills can be broken down into three phases—preparation, action, and follow-through—but you can have as many phases as you think apply to the movement of interest. Rewind the tape and use the "pause" and "frame" advance functions to count the number of video frames in the skill and calculate the times and percentages for each phase of the skill. Most VCRs show every other field, giving you a video "clock" with 30 pictures per second. Note, however, that some VCRs show you every field (half of interlaced video) so your clock will be accurate to l/60th of a second. How could you check what your or the classes' VCR does in frame advance mode? How close was your qualitative judgment to the more accurate quantitative measure of time?
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 prepared to give your reasons (cost, time, accuracy, need, etc.) for believing that one approach might be better than another.
1. Is the patient doing the lunge exercise correctly?
2. Is athlete "A" ready to play following rehab for their injured ACL?
1. Should pole vaulter "B" change to a longer pole?
2. Is athlete "A" ready to play following rehab for their injured ACL?
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