Conchola, E. C., Thiele, R. M., Thompson, B. J., & Smith, D. B (2014). Gender-related effects of neuromuscular fatigue on the electromechanical delay of the leg extensors and flexors. Medicine & Science in Sports & Exercise, 46(5), Supplement abstract number 95.

This study investigated the effects of a fatigue-inducing bout of submaximal intermittent isometric contractions on the electromechanical delay of the leg-extensors and flexors in college-aged females (N = 20) and males (N = 21). Ss participated in a familiarization trial followed by two randomly ordered experimental fatigue sessions separated by ~7 days. Experimental trials involved testing of either the leg-extensor or flexor muscles only, on each respective test day. All sessions began with Ss performing maximal voluntary contractions followed by a fatigue-inducing protocol consisting of intermittent isometric contractions of the leg extensors or flexors using a 0.6 duty cycle (6-second contraction, 4-second relaxation) at 50% of maximal voluntary contractions until volitional fatigue. Maximal voluntary contractions were again performed at 0, 7, 15, and 30 minutes post-fatigue. Electromechanical delay was calculated as the time (ms) difference between EMG and torque onset.

There was no significant three-way or two-way interaction for time × gender or muscle × gender. However, there was a two-way interaction for muscle × time. For muscle × time, the electromechanical delay was greater for the leg flexors at all post-fatigue time phases compared to pre-fatigue, but was only greater at immediately post-fatigue for the leg-extensors.

Implication. Fatigue-induced increases in electromechanical delay exhibited differential recovery patterns between muscles such that the flexor electromechanical delay values had no recovery within 30 minutes compared to more rapid recovery for the extensors. However, no gender-related differences were observed for the fatigue-induced electromechanical delay responses.

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