Association of a trunk endurance–strength composite with lower-extremity dynamic balance in physically active college students: relative roles of hip abductor strength and weight-bearing ankle dorsiflexion distance

Objective To examine the association between a trunk endurance–strength composite and the Y-Balance Test Lower Quarter (YBT-LQ) composite score in physically active college students, and to determine whether this association remained independent after simultaneous adjustment for hip abductor strength and weight-bearing ankle dorsiflexion distance. Methods This cross-sectional study included 263 college students majoring in sport-related disciplines or maintaining longstanding exercise habits. The YBT-LQ composite score was the primary outcome, the trunk endurance–strength composite was the primary exposure, and hip abductor strength and weight-bearing ankle dorsiflexion distance were specified as key competing explanatory variables; these continuous variables were standardized before entry into the regression models. Correlation analyses and hierarchical regression models were used to assess independent associations after adjustment for sex, age, body mass index, training exposure, injury history, low back pain, and sport background. Bootstrap single-mediator models were then applied to examine potential statistical pathways. Results Bivariate analyses showed that the trunk endurance–strength composite was moderately positively correlated with the YBT-LQ composite score (r = 0.39). Hip abductor strength (r = 0.64) and weight-bearing ankle dorsiflexion distance (r = 0.42) were also positively correlated with the YBT-LQ composite score, with hip abductor strength showing the strongest association. After adjustment for covariates, the trunk endurance–strength composite remained independently associated with the YBT-LQ composite score (β = 0.28, p = 0.011). After further simultaneous inclusion of hip abductor strength and weight-bearing ankle dorsiflexion distance, model explanatory power increased from 0.281 to 0.587; hip abductor strength (β = 0.59, p < 0.001) and weight-bearing ankle dorsiflexion distance (β = 0.33, p < 0.001) both remained significantly and positively associated with the outcome, whereas the effect of the trunk endurance–strength composite was attenuated and was no longer significant (β = 0.10, p = 0.136). Path analysis showed that when hip abductor strength was specified as the mediator, the indirect effect was significant (0.169, 95% CI 0.077 to 0.270, p < 0.001), with a proportion mediated of 0.612, whereas the direct effect was not significant ( p = 0.112). When weight-bearing ankle dorsiflexion distance was specified as the statistical pathway variable, the indirect effect was not supported (0.017, 95% CI -0.050 to 0.080, p = 0.566). No significant interactions were observed for sex or activity background ( p = 0.411 and 0.666). Conclusion In physically active college students, YBT-LQ composite performance was more directly and consistently associated with hip abductor strength and weight-bearing ankle dorsiflexion distance than with the trunk endurance–strength composite. The statistical association between the trunk endurance–strength composite and dynamic balance was largely explained by hip abductor strength.