Sex differences in muscle excitation and oxygenation, but not in force fluctuations or active hyperemia resulting from a fatiguing, bilateral isometric task

Abstract

It remains to be fully elucidated if there are sex-specific physiological adjustments within the human neuromuscular and vascular systems that contribute to symptoms of fatigue during a sustained bilateral task. This, in part, is likely due to various limitations in experimental design such as an inability to independently record force fluctuations from each limb. Objective. Therefore, the purpose of the current study was to examine the fatigue-induced changes in muscle excitation, force fluctuations, skeletal muscle tissue saturation (StO2), and muscle blood flow resulting from a sustained, bilateral task. Approach. Thirty healthy, college-aged adults (15 males, 15 females) performed a bilateral leg task at 25% of maximum voluntary isometric (MVIC). Before and after the task, MVICs were completed. Resting and post-task femoral artery blood flow (FABF) were determined. Muscle excitation was quantified as electromyographic amplitude (EMG AMP) from the right and left vastus lateralis. During the task, force fluctuations were determined independently from each leg. The StO2 signal was collected with a near-infrared spectroscopy device attached to the right vastus lateralis. The rate of change in these variables was calculated via simple linear regression. The exercise-induced magnitude of change in MVIC (i.e. performance fatigability) and FABF (i.e. active hyperemia) was determined. Main Results. There was no sex difference in the percent decline in MVIC (20.5 ± 20.1% versus 16.4 ± 3.5%; p > 0.05). There were no inter-leg differences in EMG AMP or force fluctuations. The males exhibited a faster rate of increase in EMG AMP (b = 0.13 versus b = 0.08; p < 0.001), whereas the females exhibited a slower rate of decline in StO2 (b = −0.049 versus b = −0.080). There was no sex difference in force fluctuations or change in FABF. Significance. Males and females likely have different neuromuscular strategies and muscle characteristics, but these did not elicit a sex difference in performance fatigability.