Aging and Posture Control: Changes in Sensory Organization and Muscular Coordination

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Abstract
The following study examined two aspects of balance control in the older adult: 1) the coordination of the timing and the amplitude of muscle responses to postural perturbations, and 2) 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: 1) increases in the absolute latency of distal muscle responses were observed in all older adults; 2) in five of the twelve older adults temporal reversals of proximal and distal muscle response onset were observed; and 3) 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.