Biomedical Engineering Reference
In-Depth Information
CHAPTER 5
Biomechanics
5.1 Overview
Previous chapters dealt with the movement of fluids and embedded molecules. Vari-
ous structures in the body also move while performing day-to-day activity. These
movements depend upon highly proficient neural control of motor neurons and
muscles. Movement of body structures requires force generation by muscular sys-
tem. Furthermore, many activities result in exerting pressure, tension, and shear
forces to the tissues. Understanding force distribution is essential to obtaining more
insight into the functioning of various tissues, the effect of load and overload on
specific structures of living systems, the development of prosthetic devices, and the
modeling and simulation of human movement. Furthermore, to incorporate safety
features, for example, designing seat belts in automobiles, one has to understand
the impact responses, injury tolerances, and injury mechanisms of the human body.
Biomechanics deals with examining the forces acting upon and within a biological
structure and the effects produced by these forces. Biomechanics is a broad field
with many applications and can be subdivided into four areas: anthropometry (i.e.,
measurement of humans), gait analysis, stress analysis, and impact biomechanics.
Some of the applications of each area are listed in Table 5.1.
Using the fundamentals of kinematics, one can study the positions, angles, ve-
locities, and accelerations of body segments and joints during regular walking.
Conservation of momentum and energy principles, discussed in Chapter 4, are used
to assess the load and stress distribution. Complexity arises because the nature of
solids is different than fluids. In solids, effects on individual elements have to be
considered, unlike fluids, which are dealt with continuous streams of fluid without
a beginning or end. Furthermore, most of the tissues are not simple solids and pos-
sess viscous and elastic characteristics. This chapter introduces the basic elements
of biomechanics. First, the forces acting in various segments are described, assum-
ing that body parts are rigid elements. Then, the concepts of elasticity and viscoe-
lasticity are introduced. Finally, the conservation of energy principle is discussed in
the context of injury prevention.
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