The effects of age on precision pinch force control across five days of practice

The effects of age on control of fingertip forces, across five days of practice, were determined for an isometric precision pinch grip task. The task involved controlling a computer cursor so that it traveled upward and horizontally on a 45 degree template line by applying X-axis isometric force with contraction of the thumb, and Y-axis force with the index finger. Upon reaching a reverse circle target, the cursor was returned to the start by controlling the steady release of isometric force. Participants' control across the 6 segments of the template line (3 applying and 3 releasing force) was examined. Healthy participants comprised three age groups: Y20 (mean = 21 ± 4 years), O70 (mean = 70 ± 3 years) and O80 (mean = 79 ± 3 years). The results indicated that 1) overall the Y20 group was faster in completing the task than the O80 group, 2) age differences in task duration time (speed) increased over 4 days, 3) the Y20 and O70 groups, but not the O80 group, improved performance (increased accuracy and decreased within-participant variability for time and accuracy) with practice, 4) circle target proximity (segments 3 and 6) was a potent factor; all groups were slower, less accurate, and less consistent irrespective of force direction in the segments approaching a circle target goal (reverse/end). A task maneuver preceding a directional reversal of force modulation, from increasing to decreasing, was the most difficult element for the O80 group followed by the O70 and Y20 groups. These old adults improved tracing accuracy and consistency, but not performance speed with practice on this precision pinch force control task.