Age-Related Differences in Postural Adjustments on Firm and Foam Surfaces

Background: Age-related changes in postural control and altered somatosensory input may both affect balance regulation, but their combined influence on postural adjustments during external perturbations remains unclear. This study investigated the effects of age and support-surface condition on postural adjustments induced by pendulum perturbations. Methods: Forty-four healthy male Chinese participants, including 22 young adults and 22 older adults, were exposed to external perturbations while standing on firm and foam support surfaces. Surface electromyography and force-platform data were used to assess muscle activation and center-of-pressure behavior during anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs). Results: Young adults showed earlier EMG onset and greater modulation of selected postural muscles than older adults. During APAs, tibialis anterior and rectus femoris baseline-normalized EMG responses were greater on the foam surface, whereas during CPAs, soleus baseline-normalized EMG activity was greater on foam. Older adults showed greater normalized lower-limb co-contraction on the foam surface, whereas young adults showed no significant surface-related change in co-contraction. Conclusions: These findings indicate age-related differences in neuromuscular responses to compliant support conditions and suggest that older adults may rely more on lower-limb co-contraction when somatosensory information and mechanical support are altered.