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SEX-DIFFERENCES IN REPETITIONS TO FAILURE AND NEUROMUSCULAR FATIGUE OF THE ELBOW FLEXORS

Abstract

Heather Day1, Mary Wilkenson1, Micaela Dusseault1, Katie Kennedy2, Ryan Colquhoun1. 1University of South Alabama, Mobile, AL. 2Texas Tech University, Lubbock, TX.

BACKGROUND: The purpose of this investigation was to examine sex-differences in repetitions completed and changes in maximal voluntary isometric contraction (MVIC) strength following consecutive sets to failure at 80% and 30% 1-repetition maximum (1RM). METHODS: Twenty-two healthy, resistance-trained subjects (9 females) completed a single visit. Subjects arrived at the lab after abstaining from caffeine for a minimum of 8 hours and upper body exercise for at least 48 hours prior to their visit. Subjects then completed 1RM testing of a bilateral preacher curl exercise. 2-3 minutes of rest was given between each attempt, and all subject’s 1RM was found within 5 attempts. Following a 5-minute rest, subjects completed consecutive sets to volitional failure at 80% and 30% 1RM with no rest between sets. MVIC strength of the dominant arm was measured prior to (PRE) and after (POST80/POST30) each set. Each MVIC was analyzed offline to calculate peak force (PF) from the greatest 200 ms window during each MVIC attempt. RESULTS: Independent samples t-tests indicated there were no significant differences in repetitions completed between sexes at 80% 1RM (F: 7.9 ± 3.3 reps; M: 7.8 ± 2.5 reps; p=0.923). However, females completed significantly more repetitions at 30% 1RM (F: 42.9 ± 11.4 reps; M: 33.7 ± 5.9 reps; p=0.022). There was a significant Sex (M/F) × Time (PRE/POST80/POST30) interaction for PF (p=0.006). Post-hoc analyses indicated that males exhibited greater PF at all timepoints (p<0.001-0.003). For females, PF non-significantly decreased from PRE (208.3 ± 56.9 N) to POST80 (192.6 ± 51.1 N; p=0.075) and significantly decreased from POST80 to POST30 (167.2 ± 58.9 N; p=0.01). In males, PF significantly decreased across all timepoints (PRE: 388.8 ± 68.1 N; POST80: 339.4 ± 56.9; POST30: 284.9 ± 91.8 N; p<0.001-0.002). CONCLUSIONS: Our data suggest that sex-differences in repetitions to failure may be exclusive to lower loads, as both males and females completed a similar number of repetitions at 80% 1RM. Additionally, our data suggest that neuromuscular fatigue may also be sex-dependent, as PF significantly declined across all timepoints in males, but not until POST30 in females. FUNDING: This project was funded by the University of South Alabama’s Summer Undergraduate Research Fellowship and Bukstein Fellowship.

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