Greater intramuscular metabolic perturbations contribute to faster muscle fatigue development in males than females during intermittent isometric exercise

INTRODUCTION: Previous studies reported faster performance fatigability in males than females during isometric exercise, ultimately prolonging time to task failure in the latter at the same relative intensity. Several authors suggested anatomical and physiological factors as primary determinants, but it remains unknown whether exercise-related accumulation of metabolites within skeletal muscle differentially affects fatigue development in female and males.

PURPOSE: This study aimed to investigate intramuscular metabolic perturbations during fatiguing intermittent isometric knee-extensor exercise in males and females. Herein, we tested the hypothesis that greater metabolic perturbation during intermittent isometric exercise results in greater fatigue development in males compared to females. Methods: Fifteen males (M)(26±2y) and fifteen eumenorrheic females (F)(24±3y) visited the laboratory twice. During visit 1, isometric knee-extensors critical torque (CT) was estimated by a 5-min all-out test. In visit 2, participants performed intermittent isometric knee-extensor exercises to task failure at 110extensors magnitude and etiology of fatigue maximal voluntary isometric contraction (MVIC), voluntary activation (VA) and potentiated twitches (St) amplitudes were evaluated before (PRE), at 9min (MID), and at task failure (POST). At the same time points, intramuscular pH and concentrations of ATP, PCr, Cr and La were determined in vastus lateralis muscle biopsies. Results: Time to task failure was shorter in M than F (1017±498 vs 1511±506s; P