Aging increases visual dependency and disrupts sensory strategies in upright standing

Postural control depends on the integration of visual and proprioceptive inputs, yet how aging modifies this sensorimotor integration in upright standing remains unclear. We examined age-related differences in postural responses to visual and proprioceptive disturbances during upright standing by applying (i) bilateral Achilles or tibialis anterior tendon vibration and (ii) and simulated forward or backward self-motion in a virtual environment. Eighteen young [22.8 (1.6)yr] and eighteen old adults [66.3 (5.5)yr] stood on a force platform to record the center of pressure (CoP). Postural responses were quantified by CoP velocity and maximal excursion. Intra- (within similar sensory modality) and inter-modal correlations (within different sensory modalities inducing similar directional postural response) were also investigated for CoP velocity to provide insight into sensory integration strategies. Tendon vibration induced robust, direction-specific CoP changes with large increase in CoP velocity without age-related differences. Conversely, simulated forward self-motion evoked greater CoP velocity increase in old [median [interquartile range]; 70.1 [75.6]%] than young [19.2 [25.1]%; p < 0.001], whereas responses to backward simulated self-motion were similar across groups. CoP maximal excursion exhibits similar variations than CoP velocity. Correlation analyses revealed intra-modal consistency in young (Achilles/tibial anterior: r² = 0.26, p = 0.030; forward/backward simulated self-motion: r² = 0.37, p = 0.024) while old adults exhibited an inter-modal positive association between Achilles vibration and simulated forward self-motion (r² = 0.29, p = 0.021). In addition to suggest an age-related increase in visual dependency to control balance, these findings revealed that aging disrupts sensory weighting within modalities and is accompanied by a stereotyped inter-modal response, suggesting altered sensory strategies that may increase fall risk.