Changes in voluntary reaction time with age: implications for falls in the elderly

Previous studies of healthy aging subjects have demonstrated age-related changes in functional performance, with generalized slowing in gait and decreased velocity of movement in standing balance. While aging is also associated with decreased conduction time of the somatosensory evoked potential of the lower limbs and slowing or absence of deep tendon reflexes at the ankle, these changes alone do not explain functional deficits in the elderly. To further explore age-related changes in function, we have performed a battery of voluntary reaction time studies at the ankle. Early studies demonstrated that healthy elderly subjects show slowing of voluntary reaction times, but the onset of muscle activity is not significantly different than younger subjects. In this study, the analysis of EMG activity during voluntary reaction time tests demonstrates that the time to complete plantarflexion movements is significantly increased in healthy elderly subjects. This slowing of ankle movements is decreased when elderly subjects are provided with visual feedback about the target and joint position. In contrast, elderly fallers demonstrate a significant slowing in the onset of EMG activity and are not able to complete plantarflexion movements at the ankle, even with visual feedback about joint position.