Examination of sex differences in fatigability, muscle oxygenation, and neuromuscular responses during low-intensity isometric handgrip exercise

Purpose: This study investigated sex-dependent physiological responses and fatigability for a single bout of unilateral, low-intensity isometric handgrip hold to failure. Methods: Eighteen young adults (9 males, 9 females) performed pre-test maximal voluntary isometric contractions (MVICs), a handgrip exercise at 30% MVIC with their dominant (exercised) hand, followed by post-test MVICs with both hands. During the exercise, time to task failure (TTF), electromyography (EMG), mechanomyography (MMG), and near-infrared spectroscopy (NIRS)-derived muscle oxygen saturation (SmO₂) were recorded. EMG and MMG amplitude (AMP) and mean power frequency (MPF), and SmO₂ were analyzed using the initial and final timepoints of the exercise. Results: EMG AMP and MMG AMP significantly increased (p = 0.009 and p < 0.001), while EMG MPF and MMG MPF significantly decreased (p < 0.001) during the exercise, collapsed across sex. Males exhibited significantly lower SmO₂ than females at task failure (p = 0.005). TTF did not significantly differ between sexes (p = 0.705). MVIC force significantly decreased in post-test in the exercised hand (p < 0.001), but not in the non-exercised hand (p = 1.000), with males exhibiting greater overall strength than females (p < 0.001), collapsed across time and hand. Conclusion: Although males demonstrated greater muscle deoxygenation during the handgrip exercise, likely due to greater absolute strength, these differences did not lead to sex differences in neuromuscular (EMG and MMG parameters) or global fatigability (TTF and MVIC changes following exercise) nor did this unilateral task cause non-local muscle fatigue. This study offers insight into sex-based physiological differences that should be considered when prescribing or evaluating low-intensity, upper-body muscular fatiguing exercise.