Nine Fundamentals Of Biomechanics

Biomechanists measure all kinds of linear and angular mechanical variables to document and find the causes of human motion. While these variables and studies are extremely interesting to biomechanists, some kinesiology students and professionals may not find them quite so inherently stimulating. Most kinesiology professionals want to know the basic rules of biomechanics that they can apply in their jobs. This section proposes nine such principles of biome-chanics and demonstrates how they relate to scientific laws. These biomechanical tools must be combined with other tools from your kinesiology toolbox to most effectively solve movement problems. Because these principles are the application rules for kinesiology professionals, they have usually been given less-scientific names so that we can communicate effectively with our clients.

Principles and Laws

The nine principles of biomechanics that follow take the form of general principles related to human movement. It is important to realize that principles for application are not the same as scientific laws. Science is a systematic method for testing hypotheses with experimental evidence for the purpose of improving our understanding of reality. Science uses a process, know as the scientific method, for testing a theory about a phenomenon with measurements, then reevaluating the theory based on the data. Ultimately, science is interested in finding the truth, facts, or laws of nature that provide the best understanding of reality. When experimentation shows data always consistent with a theory (given certain conditions), then the theory becomes a law. Scientists must always be open to new data and theories that may provide a more accurate description or improved understanding of a phenomenon. True scientific revolutions that throw out long-held and major theories are not as common as most people think. Though news reporters often herald scientific "breakthroughs," they are usually exaggerating the importance of a small step in what is a very slow process of weighing a great deal of evidence.

Note that science is not defined as a method for making practical applications of knowledge. Technology is the term usually used to refer to the tools and methods of applying scientific knowledge to solve problems or perform tasks. Remember that in chapter 1 we noted the belief of some scholars that studying academic disciplines and doing theoretical research are worthy enterprises without any need to show any practical application of knowledge. Even in "applied" fields like kinesiology, there is a long history of a theory-to-practice, or a science-to-profession gap (Harris, 1993). Why does this gap exist? It might exist because some scholars are hesitant to propose appli cation based on what is often less-than-con-clusive data, or they might be concerned about receiving less recognition for applied scholarship. Practitioners contribute to this gap as well by refusing to recognize the theoretical nature of science, by not reading widely to compile the necessary evidence for practice, and by demanding simple "how-to" rules of human movements when these simple answers often do not exist.

This text is based on the philosophy that the best use of the science of biome-chanics is in its translation to principles for improving human movement. These principles are general rules for the application of biomechanics that are useful for most all human movements. Some of the principles are based on major laws of mechanics, many of which are hundreds of years old. For example, Newton's Laws of Motion are still used at NASA because they accurately model the motion of spacecraft, even though there are more recent advancements in theoretical physics that are only an improvement in very extreme conditions (high-energy or near the speed of light). Unfortunately, the human body is a much more complicated system than the space shuttle, and biomechanists have not had hundreds of years to make progress on theories of human movement. For these reasons, these nine principles of application should be viewed as general rules that currently fit what we currently know about the biomechanics of human movement.

Nine Principles for Application of Biomechanics

The nine principles of biomechanics proposed in this text were selected because they constitute the minimum number or core principles that can be applied to all human movements and because they provide a simple paradigm or structure to apply biomechanical knowledge. The names of the principles are put in the common language of application; however, each can be directly linked to the concepts and laws of biomechanics. Special attention has been paid to make application of these principles both friendly and consistent with the specialized terminology of mechanics. As kine-siology professionals you will know the names of the biomechanical laws and theories behind these principles, but you will need to use more applied terminology when communicating with clients. This section will provide a description of each principle, and the application of these principles will be developed throughout the text. The principles can be organized (Figure 2.5) into ones dealing primarily with the creation of movement (process) and ones dealing with the outcome of various projectiles (product).

I want to point out that these principles are based primarily on work of several bio-mechanists (Norman, 1975; Hudson, 1995) who have developed generic biomechani-cal principles for all human movements. Many biomechanics books have proposed general principles for all movements (Meinel & Schnabel, 1998); various categories of human movements like throwing, catching, and running (e.g., Broer & Zernicke, 1979; Dyson, 1986; Kreighbaum & Barthels, 1996; Luttgens & Wells, 1982); or specific movements (e.g., Bunn, 1972; Groves & Camaione, 1975). Some biomech-anists believe that general principles applicable to all sports are difficult to identify and have limited practical application due to unique goals and environmental contexts of skills (Hochmuch & Marhold, 1978). This book is based on the opposite philosophy. Kinesiology professionals should keep in mind the specific goals and contextual factors affecting a movement, but the nine principles of biomechanics are important tools for improving all human movements.

The first principle in biomechanics is the Force-Motion principle. Force-motion

Nine Principles Biomechanics
Figure 2.5. The nine principles of biomechanics can be classified into those related to movement of the body or a projectile. The human body can be a projectile, so all nine principles can be applied to the human body.

says that unbalanced forces are acting on our bodies or objects when we either create or modify movement. In quiet standing the force of gravity is balanced by ground reaction forces under our feet (Figure 2.6), so to move from this position a person creates larger horizontal and vertical forces with their legs. This simple illustration of the

Minimal Horizontal Air Resistance

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Essentials of Human Physiology

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