Rate of tension development in isometric contractions of a human hand muscle

Abstract

The amplitude and rate of tension development during both electrical stimulation and voluntary activation of a human hand muscle were compared. The contractile responses from the first dorsal interosseous muscle of 14 normal human subjects were studied to provide the experimental data. At different forces less than 400g, under conditions of both electrical stimulation and voluntary contraction, force was directly proportional to speed of contraction. This linear relationship between the speed and force of contraction, as the proportion of active motor units varied, implies that these two parameters are similarly related in motor units of various sizes. In fast voluntary contractions, the rate of rise of tension at any given force level was greater than that observed in response to repetitive stimuli delivered to the motor nerve. Even at 200 and 500 impulses per second at maximal intensity, the speed of tension development was less than that found in fast voluntary contractions. The importance of asynchronous impulses and optimum discharge sequencing in generating a faster speed of tension development in fast voluntary contractions is underscored by these findings.