Wobble-board dynamics as a scalable assay of long-latency reflex function in aging

Understanding how aging reshapes balance is essential for targeted assessment and rehabilitation. Because wobble boards impose continuous instability, their kinematics may provide a noninvasive readout of long-latency (transcortical) reflex function in ecologically valid conditions. We analyzed wobble-board dynamics in healthy younger adults ( $19\text{--}35$  y, $n=29$ ) and community-dwelling older adults ( $56\text{--}70$  y, $n=29$ ) performing with and without a concurrent cognitive load (Trail Making Task). Spatial behavior was indexed by peak angular excursion magnitudes and their RMS; temporal behavior by cycle durations. For each series, we estimated Hurst exponents ( $H$ ) using detrended moving-average analysis. Across ages and task conditions, cycle-duration series clustered near $H_{\mathrm{cycle}\mathrm{duration}}\approx 0.5$ , indicating emergent timing, and peak-angular-excursion series exhibited persistence ( $H_{\mathrm{peak}\mathrm{angular}\mathrm{excursion}}\approx 0.7$ ). Age did not affect $H$ for either measure, nor the number of cycles per trial. By contrast, older adults showed substantially larger peak angular excursions and higher root mean square (RMS) peak angular excursions than younger adults. Multivariate analyses (principal components and canonical correlations) revealed that wobble-board metrics capture variance not explained by center-of-pressure and center-of-mass measures, yielding distinct signatures differentiating individuals, conditions, and-via amplitude metrics-age groups. These results indicate that wobble-board dynamics in aging primarily differ in amplitude rather than in temporal organization or cadence of corrections. This pattern suggests that the timing of corrective responses remains intact with aging, while their effectiveness is reduced. These findings support wobble-board dynamics as a promising paradigm for assessing age-related changes in balance control. Direct validation using electromyography (EMG) and controlled perturbations is warranted to confirm that wobble-board metrics reflect long-latency reflex function.