The effects of different stretch velocities on average force of the shortening phase in the stretch-shorten cycle

The function of muscle is thought to be enhanced through the use of a stretch-shorten cycle. Although this pattern of muscle function is commonly used, optimal parameters of the cycle are not well understood. The purpose of this paper is to review the stretch-shorten cycle pattern of muscle function, as it applies to human movement, and to present a research study that investigated the effects of different stretching speeds on the average concentric forces during stretch-shorten cycles. Twenty-two women performed repeated plantar flexor stretch-shorten cycles on a Kin-Com dynamometer at approximately 60% of their isometric plantar flexor maximum. Sequential trials were recorded for 15 seconds at three different speed combinations (eccentric speed/concentric speed): 50/180 degrees/sec, 100/180 degrees/sec, and 150/180 degrees/sec. Eighteen cycles from each speed combination were chosen for analysis based on contributing to an equal plantar flexor activity among the speed combinations. Analysis of variance indicated that the speed combination that most closely approximated normal walking (50/180 degrees/sec) resulted in the highest average concentric forces. Analysis of covariance indicated that the highest forces were due, at least in part, to a higher averaged interphase force.