Aging and movement errors when lifting and lowering light loads.

The purpose was to determine the influence of movement variability and level of muscle activation on the accuracy of targeted movements performed with the index finger by young and older adults. Twelve young (27.4 ± 4.4 years) and 12 older adults (74.5 ± 8.9 years) attempted to match the end position of an index finger movement to a target position when lifting and lowering a light load (10% of the maximum). Visual feedback was provided after each trial. Movement error was calculated as the absolute distance from the target. Movement variability was quantified as the standard deviation of finger acceleration and the variability of end position across trials. The EMG activity of first dorsal interosseus (FDI) and second palmar interosseus (SPI) muscles was measured with intramuscular electrodes. Older adults exhibited greater spatial and temporal errors and greater variability in finger acceleration and end position during both the lifting and lowering tasks. Older adults lifted the load by activating FDI less but SPI the same as young adults, whereas they lowered the load by activating SPI less and FDI the same as young adults. In addition, older adults exhibited lower variability across trials in SPI activation when lifting the load and lower variability for FDI activation when lowering the load. The findings demonstrate that the decrease in spatial and temporal accuracy observed in older adults when lifting and lowering a light load to a target position was due to greater movement variability and differences in antagonistic muscle activity.