Significance of passively induced stretch reflexes on achilles tendon force enhancement.

An in vivo buckle transducer technique was applied to study the reflex contribution to ATF enhancement during passive dorsiflexion stretches. Single stretches led to a linear ATF increase in the absence of an EMG reflex response, whereas clear ATF enhancement over the passive component occurred 13-15 ms after the onset of EMG responses. To quantify the reflexly induced increase in ATF, the stretched position was maintained. The mean reflex effect was two to four times greater than the passive stretch effect.