Perhaps the most important topic in the field of exercise physiology is the muscular system. Skeletal muscles enable the organism to move. Through an in depth analyses of muscle structure, the specific mechanisms behind its function may be elucidated. It is its architecture which enables skeletal muscle to contract and relax; two processes which not only function statically, but may also have the capacity for change.
Three types of muscle are known to exist in man and animals: skeletal muscle, cardiac muscle, and smooth muscle (9:3 4). Skeletal muscle which connects to bones and joints is typically activated by motoneurons (5:121). These muscles allow for locomotion and the performance of work (13:205). In addition, they account for over a quarter of the body's weight and the major part of its energy expenditure (5:121).
A typical skeletal muscle is composed of many muscle fibers, or skeletal muscle cells. These cells are elongate and multinuclear (5:121). Moreover, the contractile material within them shows cross striations (5:121). Hence, skeletal muscle is one form of striated muscle (5:121).
Skeletal muscle fibers are formed by the fusion of elongated uninucleate cells called myoblasts (5:121). Mature fibers may be as long as the muscle that they comprise (5:121). Their lengths thus range up to several centimeters (12:3). Their diameters may be anywhere from 10 to 100 microns (5:121). The cell's nuclei tend to occur around the fiber's edge, while its interior consists mainly of the protein filaments which constitute its contractile apparatus (5:121). These filaments are grouped together in bundles called myofibrils (5:121).
Myofibrils do not exist autonomously. They are further enclosed by a cytoskeleton composed of giant proteins and intermediate filaments (14:1240).
The entire structure is bounded by the muscle fiber's cell membrane, sometimes called the sarcolemma (5:121). Wrap...