Sex-Related Differences in Performance Fatigability Independent of Blood Flow Following a Sustained Muscle Action at a Low Perceptual Intensity

The purpose of this investigation was to use the RPE clamp protocol to examine sex-related differences in performance fatigability and neuromuscular responses as the result of a sustained isometric leg extension muscle action anchored to RPE = 2. Twenty adults (10 men, 10 women) performed sustained muscle actions at RPE = 2 for 5-min. Maximal voluntary isometric contractions (MVIC) were performed prior to and following the sustained muscle actions. Neuromuscular (electromyographic and mechanomyographic) parameters and force were recorded, and the values were normalized to respective MVICs and calculated every 5% across the 5-min work bout. Femoral artery blood flow (FABF) was assessed at pretest, immediately posttest, and 5-min posttest. Polynomial regression was used to define the individual and composite normalized neuromuscular and force versus time relationships during the sustained muscle action. Mixed factorial ANOVAs were used to examine differences in performance fatigability and blood flow. For performance fatigability, the men (62.4 ± 14.4 kg–43.1 ± 11.5 kg) exhibited a significantly (P < 0.05) greater decrease pretest to posttest in MVIC than the women (44.1 ± 4.8 kg vs. 38.1 ± 6.1 kg). There were different fatigue-induced neuromuscular patterns of responses between the men and women across time. For blood flow responses, however, there was no sex-related difference, but pretest (283.3 ± 70.8 mL/min) was significantly (P < 0.05) less than immediately posttest (424.5 ± 133.5 mL/min) and 5-min posttest (324.4 ± 78.3 mL/min). Thus, men demonstrated a greater degree of performance fatigability than the women, which was independent of differences in FABF. Factors such as the neuromuscular system and muscle morphology likely contributed to the difference in performance fatigability.