Fatigability and adaptation to maximal eccentric exercise in young females and males

In addition to fatigue, performance of unaccustomed eccentric (ECC) exercise causes temporary muscle damage, initiating a protective response to minimize damage from a subsequent bout (i.e., the repeated-bout effect; RBE). Indirect evidence suggests females experience greater muscle damage following ECC maximal voluntary contractions (MVCs). If true, this could induce a larger RBE for females than males; however, the RBE has not been compared between the sexes. PURPOSE: To compare fatigue and damage induced by ECC MVCs as well as the magnitude of the RBE in females and males. METHODS: Twelve males (21.6 ± 2.2yrs; 1.8 ± 0.1m; 82.4 ± 12.4kg) and twelve females (23.5 ± 3.0yrs; 1.6 ± 0.1m; 60.1 ± 4.1kg) performed two bouts (separated by four weeks) of 200 ECC MVCs of the dorsiflexors (60°/s from an ankle angle of 90° to 30° of plantar flexion; 4 sets of 50 reps; 1min rest between sets). Isometric (ISO) MVC torque and the ratio of ISO torque responses to low vs. high frequencies of electrical stimulation (10:100Hz) were compared before and after (2, 3, 5, and 10min, as well as 2, 4, and 7d) the fatiguing protocol. RESULTS: Measures of fatigue (ECC MVC torque) and damage (ISO MVC torque and 10:100Hz ratio) did not differ for females and males for bout one (all P > 0.05). Pooled data revealed decreases of 31.6 ± 13.4% for ECC MVC torque, 25.2 ± 13.9% for ISO MVC torque (2min post-exercise) and 53.6 ± 9.0% for 10:100Hz ratio (10min post-exercise). A two-way repeated measures ANOVA determined no main effect of sex or bout for any measure except the 10:100Hz ratio. Recovery of the ratio improved between bouts for both females and males (P < 0.05). CONCLUSION: Our results suggest that an initial bout of ECC MVCs causes equivalent fatigue and muscle damage of the dorsiflexors for females and males. After bout two, acute decreases in the 10:100Hz ratio are attenuated for both groups, suggesting a similar RBE for both females and males.Health and Social Development, Faculty of (Okanagan)Health and Exercise Sciences, School of (Okanagan)Graduat