Effects of Time-Loss Injuries on Seasonal Changes in Vertical Jump Performance and Surface Electromyography in Professional Football Players: An Exploratory Study

Limited evidence exists regarding longitudinal changes in neuromuscular function throughout a competitive season and following time-loss injuries in professional football. The aim of this study was to explore the longitudinal alterations related to time-loss injuries on surface electromyography (SEMG) and vertical jump performance in professional football players. Fourteen U-23 male professional football players were assessed at two time points during the 2019–2020 competitive season. SEMG activity of the rectus femoris, vastus medialis, vastus lateralis, biceps femoris, and semitendinosus was evaluated during the bulgarian squat (BS) and single knee straight bridge (SKSB) exercises. Vertical jump performance was assessed using squat jump (SJ) and countermovement jump (CMJ) tests performed on force platforms. Participants were classified as players experiencing time-loss injuries (IPs; n = 6) or players who remained continuously available (NIPs; n = 8) according to the occurrence of a time-loss injury (>8 days). Repeated-measures ANOVA was used to examine the effects of time point, group, limb, and exercise phase. Significant time point × group interactions were observed for CMJ inter-limb asymmetry variables, with IPs demonstrating reduced asymmetry values over time. During the SKSB exercise, biceps femoris activation was significantly lower in IPs (η2p = 0.38) compared with NIPs. No consistent alterations related to time-loss injuries were identified during the BS exercise. No consistent differences related to time-loss injuries were observed in conventional vertical jump performance measures. These observations suggest that SEMG assessment during posterior-chain exercises may provide complementary information regarding neuromuscular function in professional football players experiencing time-loss injuries beyond that obtained from conventional vertical jump assessments. Nevertheless, these observations should be interpreted with caution given the small sample size, the heterogeneous injury profile, and the exploratory nature of the present investigation.