Twitch potentiation after voluntary contraction.

Twitch potentiation was studied in human tibialis anterior (TA) and plantarflexor (PF) muscles after maximal voluntary contractions (MVCs). Potentiation was greater in TA and other dorsiflexor (DF) muscles than in PF and was dependent on the intensity of the voluntary effect. It was also observed that potentiation was maximal after MVCs of approximately 10-s duration; after longer voluntary contractions, the potentiation was partially suppressed by fatigue, especially in the TA. Potentiation was significantly larger when muscles were tested in a shortened position regardless of the position at which the preceding MVCs had been performed.