Beyond Hamstring Shortness: Continuous Flexibility Is Associated With Balance and Stability but Not Sensory Measures-A Cross-Sectional Study.

backgroundHamstring flexibility may influence postural control through its effects on movement mechanics and lower extremity function. However, whether flexibility is associated equally with motor and sensory components of postural control remains unclear. In addition, previous studies have predominantly relied on categorical classifications of flexibility, which may obscure functional relationships. This study is aimed at examining the associations between hamstring flexibility and multiple components of postural control in healthy young adults.

methodsThis cross-sectional observational study included 70 healthy young adults. Hamstring flexibility was assessed using the sit-and-reach test. Postural control was evaluated through dynamic balance (Y Balance Test), postural stability (Biodex Overall Stability Index), proprioception (joint position sense), and tactile acuity (two-point discrimination). Between-group comparisons and correlation analyses were performed. Multiple linear regression was conducted to identify independent predictors of dynamic balance performance.

resultsNo significant differences were observed between participants with and without hamstring shortness in dynamic balance, postural stability, proprioception, tactile acuity, or interlimb asymmetry (all p > 0.05). Hamstring flexibility was positively correlated with right-limb YBT composite score (r = 0.298, p = 0.012), negatively correlated with Biodex Overall Stability Index (r = -0.241, p = 0.044), and weakly negatively correlated with shoulder joint position sense (r = -0.265, p = 0.027). In multiple linear regression analysis, hamstring flexibility remained an independent predictor of dynamic balance performance (B = 0.557, 95% CI 0.212-0.903, p = 0.002).

conclusionsGreater hamstring flexibility was associated with better dynamic balance performance and showed a weaker association with postural stability, whereas no robust associations were observed with sensory measures of postural control. These findings suggest that hamstring flexibility may be more closely related to motor than sensory aspects of postural control in healthy young adults. Furthermore, associations were identified when flexibility was analyzed as a continuous variable, highlighting the potential value of preserving continuous data in studies examining functional performance.