Russ, D. W., Bartholomew, D. M., Towse, T. F., & Kent-Braun, J. A. (2003). Influence of duty cycle on sex differences in fatigue during maximum-effort exercise. Medicine and Science in Sports and Exercise, 35(5), Supplement abstract 802.

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This study determined if sex differences in fatigue are due to the protocol of the investigation. Men and women were exposed to four fatigue protocols:

The fatigue index of MVCpost/MVCpre and changes in central activation ratio (CAR) were calculated for all protocols.

Ischemia and increasing duty cycle intensity increased fatigue and central activation failure in both genders. A sex difference in favor of women was found in protocols A and B but not in C or D. Increasing the duty cycle intensity from 50% to 70% eliminated the gender difference as did producing an ischemic condition.

"Interestingly, a sex difference was present with A (100% duty cycle), consistent with the possibility that force fell below a threshold for occlusion in women, but not men, due to 33% lower MVCs in women than men. This would allow greater perfusion, attenuating fatigue in women. This force threshold may be a minor factor when sufficient rest time between contractions is present." (p. S145)

Implication. Perfusion/reperfusion during exercise may play an important role in sex differences in fatigue.

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