Post-activation potentiation induced by concentric contractions at three speeds in humans
Abstract
Post-activation potentiation (PAP) is the acute enhancement of contractile properties following a short duration (<10s) high intensity contraction. Compared with isometric contractions, little is known about the PAP response induced by concentric conditioning contractions (CCs) and the effect of contractile speeds. In the dorsiflexors of 10 participants, twitch responses were measured following 5s of maximal effort concentric CCs at each of 10, 20 and 50°/s. Concentric PAP responses were compared to a maximal isometric voluntary contraction (MVC) matched for contraction time. Additionally, concentric CCs were compared to isometric CCs matched for mean torque, contraction area and time. The principal finding was that the PAP response following maximal concentric CCs was independent of contractile speed and, there was no difference in the PAP response between concentric CCs and an isometric MVC. Maximal contractions, regardless of contraction modality, likely produce sufficient Ca2+ to induce a full PAP response, and thus there was no difference between speeds or contraction type. Concentric CCs had significantly larger peak twitch torque than their isometric torque matches (49-58%), and faster maximal rates of torque development at the three speeds (62-77%). However, these responses are likely related to greater muscle activation (EMG), and not contraction modality per se. Thus, PAP responses following maximal concentric CCs are not affected by velocity and responses are not different from an isometric MVC. This indicates maximal CCs produce a full PAP response independent of contraction type (isometric vs concentric) or shortening velocity.