Surface-EMG Amplitude Differences Before and After Scheduled University Team Training Following a Standardized Warm-Up in Male Collegiate Volleyball Players

Objective: To examine acute BEFORE–AFTER changes in maximum, mean, and median surface-EMG RMS amplitudes recorded from four shoulder-girdle muscles around scheduled collegiate volleyball training sessions. Methods: Sixteen male collegiate volleyball players representing one university team participated in this exploratory prospective repeated-measures study. Surface EMG was recorded from the upper trapezius, lower trapezius, infraspinatus, and serratus anterior during muscle-specific maximal voluntary isometric effort tasks. A standardized dynamic warm-up was completed before the BEFORE assessment. Surface EMG was then recorded immediately after warm-up and before the volleyball-specific training components of the session (BEFORE), and again within 5–10 min after completion of the scheduled team-training session (AFTER), on three weekly measurement days. For each EMG outcome, the main inferential estimand was the marginal AFTER–BEFORE contrast averaged across muscles and measurement days. Linear mixed-effects models included assessment condition, muscle, measurement day, and the assessment condition × muscle term; interaction analyses were treated as exploratory because the participant-level sample comprised 16 independent experimental units. Marginal AFTER–BEFORE contrasts were adjusted across the three RMS-amplitude outcomes using the Bonferroni method. Results: Mean RMS amplitude was lower AFTER than BEFORE the training sessions by 4.16 µV (95% CI: −6.32 to −2.01; Bonferroni-adjusted p < 0.001). Maximum RMS amplitude was also lower by 5.77 µV (95% CI: −11.19 to −0.35), but this contrast was not supported after multiplicity adjustment (adjusted p = 0.115). Median RMS amplitude showed an estimated increase of 3.88 µV (95% CI: −0.19 to 7.94; adjusted p = 0.181). Exploratory assessment condition × muscle interactions were not statistically significant for any of the three RMS-amplitude outcomes. Conclusions: Only the decrease in mean RMS amplitude remained statistically supported after adjustment across the three EMG outcomes. Because both assessments were performed after the standardized warm-up, warm-up status was held constant with respect to completion of the warm-up. The AFTER assessment additionally followed the subsequent volleyball-specific training components and a 5–10-min post-session interval. Accordingly, the contrast represents a within-session AFTER–BEFORE difference associated with the intervening training exposure and temporal/order effects rather than an isolated causal effect of training. Exploratory condition × muscle interactions were not statistically significant, but the small sample does not establish equivalent responses among muscles. The findings do not establish altered mechanical force or localized neuromuscular fatigue.