Practice and endpoint accuracy with the left and right hands of old adults: the right-hemisphere aging model.

The purpose of the study was to quantify the aging-related differences in endpoint accuracy during isometric contractions of the left and right hands based on the prediction that declines in motor performance with aging may be greater for muscles controlled by the right hemisphere. Twelve young (6 men, 25 +/- 5 years) and 12 old (6 men, 76 +/- 6 years) adults performed a task that involved matching the peak of a force-time trajectory to a target. The old adults were less accurate than the young men and exhibited greater endpoint error with the left hand than the right hand on day 1, but not on days 2 and 3. Although electromyographic amplitude was similar between hands, old adults exhibited greater timing variability. These findings indicate that given sufficient practice there was no difference in endpoint accuracy between the left and right hands of old adults, which is not consistent with the prediction of an asymmetrical decline in motor performance by the right-hemisphere aging model. Conversely, an inability by an old adult to achieve similar accuracy with both hands during such tasks likely indicates an underlying motor impairment.