Sex differences in performance fatigability after a maximal intermittent fatiguing protocol with a flywheel device.

Abstract

This study aimed to determine whether sex influences neuromuscular modulation following a maximal intermittent fatiguing protocol (IFP_max) using a flywheel device (FD; moment of inertia: 0.13 kgꞏm²). A secondary objective was to assess the recovery of force and electromyographic signals. Thirty-six young adults (20 females) completed 10 sets of 10 half-squats with 3-min rest intervals. Knee extension force was assessed during maximal voluntary isometric contraction (MVC) at pre-fatigue (PRE), following the IFP_max (POST), and after a recovery of 10-min (P10). Additionally, femoral nerve stimulation, such as doublets at 100 Hz (Db₁₀₀) and 10 Hz (Db₁₀) and single twitches (Tw) were applied to obtain electrically-evoked mechanical and electromyographic responses, voluntary activation (VA), H-reflex, and superimposed and resting M-wave variables at the three time points. Although males demonstrated higher pre-fatigue MVC values, they experienced a larger decline at POST (-42% vs -31%; P = 0.032). Electrically-evoked forces remained reduced at P10 compared to PRE (P < 0.001). Males showed greater declines in peak Tw (-63% vs -51%; P = 0.049), Db₁₀ (-70% vs -58%; P = 0.021) and Db_10:100 ratio (-39% vs -30%; P = 0.041). Overall, M-wave variables showed similar decrements in both sexes. Irrespective of sex, VA and H-reflex decreased at POST (P ≤ 0.037). The IFP_max performed using a FD induced a pronounced peripheral fatigue, with contractile mechanisms being more impaired in males. In contrast, central adjustments were similar between sexes. Future research is warranted to determine the most effective strength training strategies tailored to sex-specific responses.