A-41 Free Communication/Poster - Immunology-Supplements

Abstract

Recent research suggests that neuromuscular fatigue leads to increased electromechanical delay (EMD), and that differential recovery patterns are exhibited between the leg extensor and flexor muscles. However, it is unknown whether these fatigue-induced EMD responses vary by gender. PURPOSE: The purpose of this study was to investigate the effects of a fatigue-inducing bout of submaximal intermittent isometric contractions on the EMD of the leg extensors and flexors in college-aged females and males. METHODS: Twenty (mean±SD age=21.3±1.5 yrs) females and twenty-one college-aged (age=22.0±3.5) males participated in a familiarization trial followed by 2 randomly ordered experimental fatigue sessions, separated by 7(±1) days. Experimental trials involved testing of either the leg extensor or flexor muscles only, on each respective test day. All sessions began with participants performing maximal voluntary contractions (MVCs) followed by a fatigue-inducing protocol consisting of intermittent isometric contractions of the leg extensors or flexors using a 0.6 duty cycle (6s contraction, 4s relaxation) at 50% of MVC until volitional fatigue. MVCs were again performed at 0,7,15, and 30min post fatigue. EMD was calculated as the time (ms) difference between EMG and torque onset. A three-way repeated measures ANOVA was used to analyze the EMD data. RESULTS: There was no significant three-way interaction (P=0.526), nor two way interaction for time × gender (P=0.948) or muscle × gender (P=0.636), however there was a two-way interaction for muscle × time (P=0.001). For muscle × time, the EMD was greater for the leg flexors at all post fatigue time phases compared to Pre (P=0.001-0.016), but was only greater at immediately Post (i.e., 0) for the leg extensors (P=0.001). CONCLUSIONS: These findings showed that fatigue-induced increases in EMD exhibited differential recovery patterns between muscles such that the flexor EMD values had no recovery within 30min compared to more rapid recovery for the extensors. However, no gender-related differences were observed for the fatigue-induced EMD responses. These findings may have implications for performance and injury risks following fatiguing tasks, with the duration of the effects being muscle but not gender specific.