The muscular system includes all the skeletal muscles that can be controlled voluntarily. Most of the muscle tissue in the body is part of this system, and approximately 700 skeletal muscles have been identified. Some are attached to bony processes and others to broad sheets of connective tissue, but all are directly or indirectly associated with the skeletal system. Rather than attempt to survey all 700 skeletal muscles, we will focus on a relatively small but representative number of muscles, about 20 percent of the total. To simplify the memorization, we have organized these muscles into anatomical and functional groups.

The shape or appearance of each muscle provides clues to its primary function. Muscles involved with locomotion and posture work across joints, producing skeletal movement. Those that support soft tissue form slings or sheets between relatively stable bony elements, whereas those that guard an entrance or exit completely encircle the opening.

At the level of the individual skeletal muscle, two factors interact to determine the effects of its contraction: (1) the anatomical arrangement of the muscle fibers and (2) the way the muscle attaches to the bones of the skeletal system. We can understand the performance of muscles in the body in terms of basic mechanical laws. The analysis of biological systems in mechanical terms is the study of biomechanics. In this chapter, we examine the biomechanics and gross anatomy of the muscular system.
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