Voluntary rate of torque development is impaired after a voluntary versus tetanic conditioning contraction

Introduction: Both voluntary and evoked conditioning contractions will potentiate muscle twitch contractile properties. The response of a voluntary contraction to each condition type is not well understood but it may be a more functional model than evoked twitch potentiation.

Methods: Baseline measurements from tibialis anterior included: maximal isometric twitch torque and rate of torque development (RTD); maximal evoked 50-Hz torque; and maximal voluntary ballistic RTD. Potentiation was induced by a 10-s voluntary or tetanic contraction (∽78% MVC), followed by 2 twitches and 2 ballistic contractions.

Results: Twitch properties (torque and RTD) were potentiated equally after each conditioning contraction. Ballistic RTD was greater post-tetanus (390.2 ± 59.3 Nm/s) than post-voluntary (356.4 ± 69.1 Nm/s), but both were reduced from baseline (422.0 ± 88.9 Nm/s).

Conclusions: Twitch potentiation was similar between conditioning contraction types, but ballistic RTD was lower after post-tetanus than post-voluntary. The results indicate central inhibition or fatigue concurrent with peripheral potentiation.