Postactivation potentiation in human knee extensors during dynamic passive movements.

Abstract

Postactivation potentiation (PAP), i.e., the increase in twitch torque following a maximal voluntary conditioning contraction, has been shown to depend on muscle contractile conditions (e.g., muscle length). Few studies, however, have investigated the extent of twitch PAP under dynamic conditions in human subjects. Therefore, the aim of the present experiment was to test the twitch PAP during passive dynamic movements following isometric conditioning contractions on nine healthy men. Maximal twitches were evoked on the knee extensor muscles before and exactly 5 s after a 3-s conditioning maximal voluntary isometric contraction. PAP was determined at a constant joint angle under isometric conditions, during and immediately after passive shortening and lengthening with slow and fast angular velocities (30 and 150 degrees .s). Our results indicate a significant PAP increase with increasing shortening angular velocity (34.6 +/- 13.2% and 51.9 +/- 21.1% at 30 degrees .s and 150 degrees .s velocities, respectively), whereas PAP was significantly lower during lengthening (15.2 +/- 15.2%) as compared with isometric conditions (28.5 +/- 18.3%). Similar results were obtained when PAP was determined isometrically but immediately following passive shortening or lengthening (30 degrees .s). These data indicate that PAP affects dynamic torque production capacity and that PAP is dependent on contractile conditions. Furthermore, the similar extent of PAP during and immediately after passive movements suggests a PAP history dependency. Our results therefore suggest that PAP is recommended more for improving shortening performance than for lengthening.