Sex Differences in Muscle Activity After a Maximal Intermittent Fatiguing Protocol With a Flywheel Device

To study the possible sex differences in muscle activity after a maximal intermittent fatiguing protocol (IFPmax) performed with a flywheel device.

Fifteen males and 17 females completed 10 sets of 10 half-squat repetitions with 3 minutes of passive recovery between sets as the IFPmax. Before and after the IFPmax, maximal isometric half-squat and countermovement jump were performed. Surface electromyography was used to analyze muscle activity in the gluteus maximus, vastus lateralis, rectus femoris, vastus medialis, biceps femoris, and semitendinosus.

Both sexes exhibited a similar decline in maximal isometric half-squat force and countermovement-jump flight time after the IFPmax. Although males demonstrated higher baseline power performance (F ≥ 4.99, P ≤ .013, ηp2≥.14), these differences were no longer significant at the end of the fatiguing protocol. A more pronounced decrease in electromyography activity of the agonist musculature was observed in males (F ≥ 4.84, P ≤ .036, ηp2≥.14), whereas delta analysis revealed a greater increase in antagonist muscle activity in females (P < .05). Hip-to-knee cocontraction ratio increased similarly in both sexes (F ≥ 10.14, P ≤ .004, ηp2≥.27). However, males and females adopted distinct muscle-activation patterns as fatigue developed.

Sex-related differences in muscle activity following an IFPmax performed with a flywheel device suggest the potential for higher training volumes and/or shorter recovery intervals for females. These findings provide valuable insights for the individualization and optimization of training protocols based on sex differences.