Effect of Extreme Intensity Exercise on Muscle Force Between Men and Women

While the effects of severe intensity exercise on muscle contraction and performance have been extensively studied, little is known about the impact of extreme intensity exercise. Previous data in our laboratory have shown that potentiated twitch force (Q tw‐ ; an index of peripheral fatigue) remained decreased following severe intensity knee extension exercise for > 2 minutes, while Q tw recovered quickly (< 2 min) after task failure (T lim ) following extreme intensity exercise (T‐ lim < 2 min). However, the recovery during this time has not yet been investigated. Further, previous studies have found sex differences in exercise tolerance at relatively lower intensities (20–50% maximal voluntary contraction; MVC) that are lost during greater intensities (> 60% MVC), suggesting similar mechanisms of fatigue for both sexes at greater intensities. Therefore, the purpose of this study was to test the hypotheses that Q tw would 1) be significantly decreased following severe and extreme exercise in both men and women, 2) significantly recover to baseline values within 2 minutes after exercise cessation following extreme exercise but remain suppressed following severe exercise, and 3) be greater in men than women following severe exercise but would not be different following extreme exercise. Six men (23 ± 3 yr; 87.5 ± 16.1 kg; 179.3 ± 2.3 cm) and six women (22 ± 1 yr; 58.3 ± 3.38 kg; 158.8 ± 4.2 cm) performed 2 intermittent isometric knee extension tests to exhaustion at 40% (severe intensity) and 70% (extreme intensity) maximal voluntary contraction (MVC) in random order. Changes in Q tw were examined immediately following exercise and compared to baseline values. Post exercise Q tw were compared between 0, 90, and 150 s following exercise. T‐ lim was significantly shorter in men compared to women at 40% MVC (p = 0.001), but not at 70% MVC (p = 0.13). Q tw was significantly reduced in men and women immediately following both exercise intensities (p < 0.001), with men having a greater reduction in Q tw compared to women at both 40% MVC (11.6 ± 2.1 vs 6.2 ± 2.4 kg; p = 0.002) and 70% MVC (9.8 ± 2.6 vs 4.8 ± 0.7 kg; p = 0.001). However, the reduction was not different between intensities within men and within women. Q tw increased significantly between 0 and 90 s of recovery, and further to 150 s in men following both intensities, whereas in women Q tw increased from 0 to 90 s, but no further at 150 s. Nonetheless, men showed significantly less recovery from fatigue at 90 and 150 s following both intensities compared to women. Lastly, following extreme exercise, Q pot in women was not different than pre‐exercise values within 90 s, whereas Q pot in men remained significantly lower than pre‐exercise values throughout 150 s of recovery (p < 0.001). These current data suggest men develop a greater amount of peripheral fatigue compared to women during intermittent isometric exercise during both severe and extreme intensity exercise. Further, the increased tolerance to severe exercise observed in women might be attributed to less peripheral fatigue accumulation (ΔQ tw ) compared to men. Interestingly, no sex differences were observed in extreme exercise tolerance despite decreases in Q tw that mirrored those observed during severe exercise. Finally, Q pot in women was significantly recovered within 90 s, whereas Q pot in men remained reduced throughout recovery.Reduction in Q pot for men and women during severe (40% MVC) and extreme (70% MVC) exercise. Note: Q pot in women was significantly recovered within 90 s (i.e., not significantly different than pre‐exercise values; dashed line), whereas Q pot in men remained reduced throughout recovery. * Significantly lower than pre‐exercise values.