Age-related changes in anticipatory postural adjustments associated with arm movements.

This study investigated the effects of age on the feedforward activation of postural muscles in advance of reaction time arm movements. Fifteen young (mean age 26 years) and 15 older (mean age 71 years) adult subjects were instructed to rapidly push or pull on a hand-held manipulandum. Postural muscle response onset latencies of the lower leg were significantly increased in the older adult group in three of the four conditions when compared to the young adult group. In addition, prime mover muscle response onset latencies of the upper arm showed a large, significant increase in older adults beyond that due to the slowing of the postural response. The results suggest two conclusions. The voluntary control system may be affected to a slightly greater degree with age resulting in slower voluntary movement in the elderly. Or, deterioration of the postural control system with age slows the speed of voluntary movement by delaying the onset of the voluntary muscle response.