Postactivation Potentiation of Force Is Independent of H-Reflex Excitability

in International Journal of Sports Physiology and Performance
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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 fexion actions.

Methods:

Plantar flexor twitch torque, soleus H-reflex amplitudes, and the rate of force development of explosive plantar fexion were measured before and after 4 separate conditioning trials (3 × 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.

Hodgson is with the Rehabilitation Neuroscience Laboratory and the School of Physical Education, University of Victoria, Victoria, BC; Docherty is with the School of Physical Education, University of Victoria, Victoria, BC; and E. Paul Zehr is with the Rehabilitation Neuroscience Laboratory, University of Victoria, Victoria, BC, and International Collaboration on Repair Discoveries (ICORD), Vancouver, BC, Canada.