Muscle fiber resting length

Whole muscles are composed of groups of muscle fibers, which vary from 1 to 400 mm in length and from 10 to 60 tm in diameter. Muscle fibers, in turn, are composed of groups of myofibrils (Fig. 6.2b), and each myofibril is a series of sarcomeres added end to end (Fig. 6.2c). The sarcomere is both the structural and functional unit of skeletal muscle. During contraction, the sarcomeres are shortened to about 70 percent of their uncontracted, resting length. Electron microscopy and biochemical analysis have shown that each sarcomere contains two types of filaments thick filaments, composed of myosin, and thin filaments, containing actin (Fig. 6.2d). Near the center of the sarcomere, thin filaments overlap with thick filaments to form the AI zone (Fig. 6.2c). 

Tendons are bundles of tough connective tissue fibers that connect muscle to bone. They vary in length and size depending on where they are in the body (and whose body it is). Ligaments are short bundles of fibrous tissue in and around joints. They stabilize the joint by keeping the bones in position both during movement and at rest. Both tendons and ligaments have been used as... 

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