Identification of time-varying properties of the human triceps surae stretch reflex: II. rapid imposed movement

Changes in the gain relating small imposed movements and the evoked EMG were studied throughout a large stretch of the human triceps surae muscles using an ensemble time-varying system identification technique. EMG stretch reflex gain was found to co-vary strongly with background EMG during steady-state conditions, but gain increased less than EMG during the stretch-evoked burst of activity and was essentially zero during the post-stretch "silent period". Possible mechanisms are discussed.