Bilateral Grasp Force Coordination in Young and Old Adults.

Abstract

The purpose of these experiments was to examine the coordination of bilateral isometric grasp force production in young and old adults during maximum and submaximum force tasks produced either simultaneously or sequentially. Thirty-six adults (12 young, 18-28y; 12 old, 65-75y and 12 old-old, 76-85y) participated in the first experiment involving maximum isometric grasp-grasp and grasp-pinch force. In the dominant hand, a force deficit was observed in bilateral compared to unilateral tasks in young adults during both maximum isometric grasp-grasp, -12 ± 5% (p < .05), and grasp-pinch, -20 ± 4% (p < .001), tasks. The force deficit was absent in the old group in both grasp, +4 ± 12%, and grasp-pinch, +5 ± 13%, tasks, as well as in the old-old group during both grasp, -9 ± 8%, and grasp-pinch, -9 ± 8%, tasks. Data therefore suggest that the force deficit is absent in both tasks with aging. These findings are consistent with the mechanism of transcallosal inhibition and degeneration of the corpus callosum in aging. The second experiment examined sequential submaximum maintained grasp force tasks. Twenty-four adults (12 young, 18-28y, and 12 old, 75-85y) participated in this experiment. During sequential light or firm grasp tasks, maintained grasp force in young adults decreased during force rise, -2 ± 1% (p < .05), or relaxation, -13 ± 2% (p < .01), in the opposite hand. The decline in maintained force was even greater in old adults during force rise, -5 ± 1% (p < .01), and relaxation, -15 ± 1% (p < .01), in the opposite hand. Overall, the decline found in maintained grasp during relaxation of the opposite hand was greater than observed during force rise, p < .001, for both age groups. These results were independent of the hand used to maintain force and the force level exerted in either hand. Divided attention is suggested to at least partially account for the decline in maintained force, with the anterior cingulate cortex posited as the locus for the integration of bilateral force production and attention.