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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