Contraction of muscles generates tension,which allows muscles to shorten and thereby perform work.The contraction strength of skeletal muscles must be sufficiently great to overcome the load on a muscle in order for that muscle to shorten.
The contractions of skeletal muscles generally produce movements of bones at joints, which act as levers to move the loads against which the muscle's force is exerted. The contractile behavior of the muscle, however, is more easily studied in vitro (outside the body) than in vivo (within the body). When a muscle—for example, the gastrocnemius (calf muscle) of a frog—is studied in vitro, it is usually mounted so that one end is fixed and the other is movable. The mechanical force of the muscle contraction is transduced (changed) into an electric current, which can be amplified and displayed as pen deflections in a multichannel recorder (fig. 12.17). In this way, the contractile behavior of the whole muscle in response to experimentally administered electric shocks can be studied.
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