Glossary of Biomechanical Terms, Concepts, and Units

Abstract

In the last decade, physical therapists have recognized that the field of biomechanics has become an area of study that can contribute significantly to the profession; therefore, it has become a part of most curricula. Biomechanics represents an amalgamation of several different fields including mechanics, physics, engineering, anatomy, physiology, and mathematics. More recently, elements of computer science and electronics have also become integral components. The breadth of knowledge required is therefore substantial, and we are not surprised about the lack of precision concerning terminology in certain areas. A lack of formal background during professional preparation may lead to the misuse of some terms because of the relative infancy of biomechanics. The simultaneous inclusion of biomechanics into the body of knowledge of other fields such as orthopedics, ergonomics, prosthetics, and podiatry have sometimes led to disagreement over basic definitions and concepts, which have developed different meanings in different fields. For these reasons, we found it appropriate to put in one place a collection of frequently used biomechanical terms that have consistent meanings across the various disciplines. This glossary presents definitions, synonyms, units, and commonly used abbreviations for biomechanical terms. We consulted many standard works in biomechanics for the collection of these terms. These references are given in the suggested readings so that the flow of the article is not interrupted. The final responsibility for the definitions rests, of course, with us; we have also presented our own opinions on terms that many people consistently use incorrectly or ambiguously. The definitions have been grouped into the following general sections: kinematics, forces, kinetics, computational methods, muscle mechanics, mechanics of materials, instrumentation, body segment variables, units, index, references, and suggested readings. The following general format has been used for entries:

Mechanical Misconceptions: Have we lost the "mechanics" in "sports biomechanics"?

“…Joint force can be obtained with inverse dynamics (herein, we will refer to these as net joint forces). This same construct was defined as joint reaction force by Rodgers and Cavanagh [3], which was popularized by Winter [15] thereafter: "The equal and opposite forces that exist between adjacent bones at a joint caused by the weight and inertial forces of the two segments. Joint reaction force is a fairly abstract concept useful in mathematical analysis but not much use in practice.…”

“…Joint reaction force is a fairly abstract concept useful in mathematical analysis but not much use in practice. This quantity must not be confused with joint forces that include the effects of muscle action" (p. 1889, Rodgers and Cavanagh [3]). …”

“…Winter [15] and Rodgers and Cavanagh [3] proposed that such forces be termed bone-on-bone force, or simply joint force:…”

“…Joint forces are the result of muscle forces, gravity, and inertial forces (usually, muscle forces are responsible for the largest part)" (p. 1889, Rodgers and Cavanagh [3]). …”

“…However, both the application of and language surrounding these constructs are not always adhered to in biomechanics. As a result, a number of papers [2,3,4,5,6,7], editorials [8,9,10], letters to the editor [11,12], and even reviews [7,13,14] have addressed these mis-or ambiguous applications of mechanical principles; nevertheless, proper use of key principles and terminology remains inconsistent. Here we expound upon this prior work, with specific emphasis on misconceptions relevant to sports.…”