The effect of a small stretch on the latency relaxation and the short-range elastic stiffness in isolated frog muscle fibres.

The amplitude of the latency relaxation and the stiffness of the short-range elastic component (SREC) were determined in single muscle fibres before and immediately after subjecting the fibre to a sudden small stretch at constant velocity. After the stretch the amplitude of the latency relaxation was reduced compared to the value obtained before the stretch provided that the velocity of stretch exceeded about 1 mm . ms-1 per half-sarcomere and that the amplitude of the stretch was sufficient to reach the stationary response of the SREC. The effect of the stretch on the amplitude of the latency relaxation subsided after about 4 ms. A reduction of the amplitude of the latency relaxation was accompanied by a reduction of the short-range elastic stiffness. This result is discussed in terms of the various hypotheses put forward to account for the generation of the latency relaxation.