Skeletal muscle: length-dependent effects of potentiating agents.

The ability of vertebrae skeletal muscle to contract more vigorously than normal in the presence of potentiating agents depends on the initial length of a muscle cell. Other factors such as the intracellular calcium ion transient, temperature, chemical nature of the potentiating agent, and the ratio of intrinsic twitch to tetanic force influence the degree of contractile potentiation but cannot account for the length dependence. At least part of a muscle cell seems normally less than fully active during contractions not only at short lengths but also at optimal sarcomere lengths.