Gender differences in neuromuscular fatigue after 21km run

Aim: Little is known about the gender differences in fatigue during prolonged locomotor exercise. This study investigated possible gender differences in central and peripheral fatigue and in the rate of force development in the knee extensor muscles after 21 km run. Methods: Ten males and eight females amateur runners (aged 25 to 50 years) were evaluated before and immediately after the “Run for Science” 21 km race. Knee extensors forces were obtained under voluntary and electrically evoked isometric contractions. Maximal voluntary isometric contraction (MVC), rate of force development (RFD), and relative RFD (i.e. RFD/MVC) were obtained. Electrically elicited twitches were recorded during MVC [interpolated twitch (IT)] and at rest [resting twitch (RT)], and the level of voluntary activation (VA) during each MVC was calculated as VA(%)=100(1-IT/RT). Electromechanical delays (EMD) were calculated as the difference between the onset of electromyographic activity in vastus lateralis and the onset of force production. Results: Changes in most neuromuscular variables were found similar between males (former values) and females (latter values), such as MVC (-14%, - 11%, p=0.41), RFD (-20%, -11%, p=0.24), relative RFD (-1%, - 7%, p=0.14), voluntary activation (-7%, -4%, p=0.54), and resting twitch (+ 2%, - 8%, p=0.20). The EMD showed different behaviours between genders (p=0.02) since were found increased in females (+20%) and decreased in males (-19%). Conclusions: Contrary to the expectation, no difference in voluntary force expressions (MVC and RFD) was observed between genders. Otherwise, it was expected the absence of difference in central and peripheral fatigue between genders. The greater impairment of electromechanical delay in females than in males was a novel results for this type of prolonged running. The small sample size may have limited the capacity to distinguish between groups.