Age-related changes in grasping force modulation.

The aim of this study was to determine the effect of age on the modulation of forces produced by the digits and to determine the effects of practice on the control of these forces in young and older adults. Young (n = 14, 19-28 years) and old (n = 12, 67-75 years) adults used a precision grip to perform a variable force-tracking task (sine wave, 5-25% of maximum voluntary force) with their dominant hand. Participants performed 100 practice trials over 2 consecutive days. Results indicated that both groups improved accuracy of force tracking as a result of practice. Younger adults performed the task at a higher level in pre- and post-test conditions compared with older adults. Younger adults showed improvements in force control in force generation and release phases. Older adults reached performance levels comparable with younger adults' pre-test performance, but only after extended practice. In contrast to young adults, older adults' performance during the force release phases remained quite variable. These data suggest that older adults are impaired in the accurate release of grip force. Varied force release patterns that disrupt the precision of force modulation may contribute to older adults' diminished dexterous abilities.