Clark, B., Collier, S. R., Manini, T. M., & Ploutz-Snyder, L. L. (2004). Sex differences in muscle fatigability and neuromuscular activation patterns of the human quadriceps femoris. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 1892.

This investigation determined if the fatigability of the quadriceps femoris varies by gender under ischemic and perfused conditions; and 2) to determine if differences in neuromuscular activation patterns exist. Ss (M = 11; F = 11; ages 20-39 yr) performed a sustained contraction at 25% of maximal force under conditions of ischemia and normal muscle blood flow (non-ischemic). For the non-ischemic condition electromyographic activity was recorded from the vastus lateralis, rectus femoris, vastus medialis, and biceps femoris muscles, and analyzed for fatigue-induced changes in the amplitude and bursting activity (transient changes in motor unit recruitment) of the signal. Additionally, torque fluctuations (tremor) were quantified as an indirect measure of excitatory drive.

Females had a longer endurance time during non-ischemic conditions, but not during ischemia. EMG data demonstrated fatigue induced gender differences in the neuromuscular activation patterns of the rectus femoris. The most noticeable differences were the males failing to recruit the rectus femorisas the fatiguing contraction progressed and females achieving a greater relative activation. Additionally, during the non-ischemic condition, females exhibited a greater tremor during the last-third of the contraction, and had a tendency for increased bursting activity.

Implication. Gender differences in intramuscular blood flow and/or muscle metabolism are in part responsible for the female advantage in fatigue-resistance. Additionally, fatigue-induced gender differences were observed in the neuromuscular activation pattern of the quadriceps femoris but not the other muscles. These findings suggest there are fatigue-induced gender differences in supraspinal descending drive, and/or excitability of the human neuromuscular system.

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