Aging and posture control: changes in sensory organization and muscular coordination.

The following study examined two aspects of balance control in the older adult: the coordination of the timing and the amplitude of muscle responses to postural perturbations, and the ability of the participant to reorganize sensory inputs and subsequently modify postural responses as a consequence of changing environmental conditions. Coordination of muscle activity in postural responses of twelve elderly (sixty-one to seventy-eight years) participants were compared to those of young (nineteen to thirty-eight years) adults using a movable platform and recording the electromyographic activity of muscles of the legs. The following changes were noted in the timing and amplitude of muscle activity within a postural response synergy: increases in the absolute latency of distal muscle responses were observed in all older adults; in five of the twelve older adults temporal reversals of proximal and distal muscle response onset were observed; and there was a breakdown in the correlation of the amplitude of responses within a synergy. The ability of the older adult to balance under conditions of reduced or conflicting sensory information was also impaired. When confronted with functionally inappropriate visual and/or somatosensory inputs, half of the older group lost balance. In most instances, however, the older participants were able to maintain stability during subsequent responses to conflicting stimuli.