Voluntary activation and mechanical performance of human triceps surae muscle after exhaustive stretch-shortening cycle jumping exercise.

The purpose of this study was to examine neuromuscular factors that may contribute to post exercise force loss and subsequent recovery after exhaustive stretch-shortening cycle (SSC) exercise. Six subjects were fatigued on a sledge apparatus by 100 maximal rebound jumps followed by continuous submaximal jumping until complete exhaustion. Exercise-induced changes in neuromuscular performance were followed up to 7 days post exercise. The total number of jumps in the SSC exercise ranged from 336 to 1392. The SSC exercise induced a significant immediate plantarflexion torque decline of 29, 38 and 44% ( P<0.05) in maximal voluntary contraction and evoked maximal twitch and low-frequency (LF) stimulation, respectively. The higher the number of jumps in the SSC exercise the larger was the post exercise reduction in voluntary activation as well as in contractile force ( r=-0.94, P<0.01, in both). Furthermore, a higher number of jumps augmented a delayed force recovery and late decline in stretch reflex EMG response ( r=-0.94, P<0.01). Clear differences were found in central and peripheral adaptation to the exhaustive SSC exercise between the subjects. The magnitude of post exercise contractile and activation failure as well as the delayed recovery of neuromuscular performance may have been augmented in some subjects due to their high number of jumps in the exercise.