Sex‐based comparisons in skeletal muscle fatigue and twitch potentiation

A predominance of type II fibers has been shown to result in a greater decrease in isometric maximal voluntary contraction (MVC) force during a fatigue protocol. Also, males have been shown to have a greater type II fiber percent area than females and greater fatigability. Our purpose was to examine changes in MVC and twitch force in males and females during a fatigue protocol and subsequent recovery. Nine men and twelve women performed sixteen 5‐s MVCs of the knee extensors with maximal twitches evoked during the 3‐s rest period between MVCs and every 30 s during recovery. Twitch potentiation was greatest after the 2nd MVC (males 74.8%, females 79.5%) and was lowest or most depressed following the last MVC (males 5.2%, females −11.9%). The potentiated twitch increased throughout the recovery period and was sustained above the resting twitch after 5 min (P<0.001). Males showed a greater decrease in MVC (35.7% vs. 20.6%, P<0.05); however, there was no sex‐based difference in the potentiated and depressed twitch response. Needle biopsies from subjects’ vastus lateralis muscles are currently being analyzed for fiber type distribution to assess its influence on potentiation and fatigue. Supported by NSERC.