Postactivation potentiation of knee extensor muscles in power- and endurance-trained, and untrained women.

This study compared postactivation potentiation (PAP) in knee extensor muscles after a 10 s conditioning isometric maximal voluntary contraction (MVC) in female power- (PT, n=12) and endurance-trained (ET, n=12) athletes, and untrained (UT, n=12) women aged 20-24 years. Isometric twitch characteristics of the knee extensor muscles were assessed in pre-MVC condition and during 15 min post-MVC period using supramaximal electrical stimulation of the femoral nerve by rectangular pulses of 1 ms duration. A significant (P<0.05) potentiation of twitch peak torque (Pt, 30-51% in different groups), maximal rates of torque development (50-125%) and relaxation (76-124%) occurred immediately (2 s) post-MVC. PAP declined sharply at 1-3 min of recovery, whereas a significant potentiation of twitch Pt was still present for ET athletes at 1 min, and for UT women and PT athletes at 5 min of recovery, respectively. There were no significant (P>0.05) changes in twitch contraction and half-relaxation times after a 10 s conditioning MVC. We concluded that PAP in knee extensor muscles is enhanced in PT but not in ET female athletes. The magnitude of PAP was greater when measured immediately after the conditioning MVC and its decline was slower in PT compared with ET athletes. Immediately post-MVC, twitch speed-related characteristics were potentiated to a greater extent than twitch Pt. The time-course of isometric twitch was not significantly altered by conditioning MVC.