Visual, vestibular and somatosensory contributions to balance control in the older adult.

Age- and pathology-related changes in the relative contributions of visual and somatosensory inputs to dynamic balance control were evaluated. Young adults (mean age = 25, SD = 4) were compared to older adults (mean age = 68, SD = 5). Electromyographic responses were collected when subjects' balance was perturbed on a movable platform. The amounts of visual information and of somatosensory input at the ankle were manipulated. Muscle response latencies, losses of balance, and muscle sequencing were analyzed. Muscle response latencies did not differ across age groups. Loss of balance data indicated that older adults were less stable under conditions in which peripheral vision was occluded and ankle somatosensation was limited (only foveal vision and vestibular input remaining). Older adults showed more antagonist muscle activation and used muscle sequences not seen in young adults (e.g., hip strategy). These effects were exaggerated among subjects in whom borderline pathology had been diagnosed.