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

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Abstract
Purpose: To study the possible sex differences in muscle activity after a maximal intermittent fatiguing protocol (IFPmax) performed with a flywheel device. Methods: 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. Results: 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, ), 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, ), 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, ). However, males and females adopted distinct muscle-activation patterns as fatigue developed. Conclusions: 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.

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