Unilateral Posterior-Chain Training as a Perturbation Strategy for Balance Improvements in Middle-Aged Adults

Postural instability and impairments in dynamic balance are common in aging populations and are often linked to asymmetries between the supportive and non-supportive limbs. This study investigated the effects of a four-week unilateral posterior-chain resistance training program targeting the non-supportive leg on dynamic and static balance measures in middle-aged, recreationally active adults. Twenty-seven participants (ages 40-56) performed Single-Leg Romanian Deadlifts (SLRD) twice weekly, following a progressive overload model. Balance performance was evaluated using the Y Balance Test (YBT) and the Tetrax posturography at three time points: PRE (familiarization), PRE1 (before intervention), and POST (post-intervention). Initial analysis of the supportive versus non-supportive classification showed no statistically significant improvements in either the trained (non-supportive) leg or the supportive one. However, when analyzed based on left versus right leg performance, the results revealed significant improvements in posterolateral reach in both limbs, indicating direction-specific adaptations and potential bilateral transfer effects. Posterolateral reach improved significantly in both the left leg (p = 0.008, η² = 0.170) and right leg (p = 0.022, η² = 0.137), with no change in static balance. The observed gains in dynamic balance across legs suggest that unilateral posterior-chain training may improve specific components of balance, regardless of limb dominance. Findings support the idea that unilateral posterior-chain exercises can act as perturbation-like stimuli, encouraging neuromuscular adaptations that enhance overall dynamic balance. Additionally, they also highlight the importance of clear methodological approaches to limb classification when analyzing training effects in balance research.