Does a muscle fatigue-inducing protocol alter the magnitude of functional inter-limb asymmetry in healthy adolescents?

Introduction: Inter-limb asymmetry has extensively been studied in the context of sport performance. Research has shown that inter-limb asymmetry is a complex metric influenced by numerous factors (e.g., loading protocol). However, research on inter-limb asymmetry in a fatigued state is scarce. Therefore, the purpose of this study was to assess changes in jump asymmetry magnitudes in healthy adolescents over a 72-hour period following a muscle fatigue-inducing protocol.
Methodsː Twenty-two adolescents (age = 14.6±1.8 years, 32% female) participated in the current study. The fatiguing protocol involved 10 sets of 10 maximal vertical jumps, with a one-minute rest interval between sets. The functional test battery consisted of the Single-leg 10-jump (SL10J), single-leg countermovement jump (SLCMJ), and single-leg hop jump (SLHJ) asymmetry, measured at baseline, immediately post-protocol, and at 24, 48, and 72 hours post- fatiguing protocol. Bioelectrical impedance analysis-derived phase angle was used to assess the level of muscle damage, while muscle soreness was evaluated using the Visual Analog Scale (VAS). Bilateral countermovement jump (BCMJ) and bilateral horizontal jump (BHJ) were used to indicate changes in absolute jump performance across test occasions. Normality was assessed using the Shapiro-Wilk test. A one-way repeated measures mixed design ANOVA was conducted to examine differences in the magnitude of inter-limb asymmetry over time. For non-normally distributed data, Friedman and Wilcoxon tests were applied. Kappa coefficients were calculated to evaluate the consistency of the limb that performed better across tests (i.e., task specificity) and the consistency of the limb that displayed the highest jump performance over time (i.e., time specificity).
Resultsː A significant increase in SL10J asymmetry was observed 48 hours post-protocol (p<0.001), while no significant changes were detected immediately post-protocol or at 24 and 72 hours post-protocol (p=0.462–0.766). No significant changes were found in SLCMJ (p=0.714) or SLHJ (p=0.468) asymmetry at any time point. BIA did not indicate significant muscle damage, although a significant increase in muscle soreness (VAS) was recorded. Kappa values indicated slight to moderate agreement for task specificity (κ=-0.123–0.493) and slight to substantial agreement for time specificity (κ=-0.137–0.732).
Conclusionsː SL10J asymmetry significantly peaked 48 hours after the fatigue-inducing protocol before returning to baseline values. In contrast, no significant changes were observed in SLCMJ and SLHJ asymmetry. Consistent with previous research, our findings indicate that inter-limb asymmetry is both task- and time-specific. However, the results show greater consistency in the direction of asymmetry between 24 and 48 hours post-protocol for both SLCMJ and SL10J. These findings suggests that repeated jump tests, such as the SL10J, may be more sensitive to detecting fatigue-induced changes in asymmetry.