Postactivation potentiation of force is independent of h-reflex excitability.

UNLABELLED The contractile history of muscle can potentiate electrically evoked force production. A link to voluntary force production, related in part to an increase in reflex excitability, has been suggested. PURPOSE Our purpose was to quantify the effect of postactivation potentiation on voluntary force production and spinal H-reflex excitability during explosive plantar flexion actions. METHODS Plantar flexor twitch torque, soleus H-reflex amplitudes, and the rate of force development of explosive plantar flexion were measured before and after 4 separate conditioning trials (3 x 5 s maximal contractions). RESULTS Twitch torque and rate of force production during voluntary explosive plantar flexion were significantly increased (P < .05) while H-reflex amplitudes remained unchanged. Although twitch torque was significantly higher after conditioning, leading to a small increase in the rate of voluntary force production, this was unrelated to changes in reflex excitability. CONCLUSION We conclude that postactivation potentiation may result in a minor increase in the rate of voluntary isometric force production that is unrelated to neural excitability.