Abstract

Exceedingly large grip forces that many older adults employ whin lifting objects with a precision pinch grip may compensate for a reduced capability to produce a stable isometric force. We examined the within-trial variablity of isometric force in old (68-85 yrs.) and young (22-35 yrs.) human subjects a) when they were asked to produce a constant pinch force at 3 target levels with external support of the ar, hand, and force transducer and b) when they were asked to grasp, lift, and hold a small test object with a precision grip. Pinch force produced in the first task was equally stable acrtoss the 2 subject groups during analysis intervals that lasted 4 s. Elderly subjects produced grip forces when lifting objects that averaged twice as much as those produced by young subjects. Force variability during the static (hold phase of the lift for the old subjects was comparable with that used by young subjects, after adjusting for the difference in grip force. Failure to observe less stable grip force in older adults contradicts a similar recent study. Differences in task (isometric grip force versus isometric abduction torque of a signle digit) may account for this conflict, however. Thumb and finger forces for grip are produced through coactivation of many muscles and thus promote smooth force output through temporal summation of twitches. We conclude that peripheral reorganization of muscle in older adults does not yield increased instability of precision grip force. Force instability may affect grip configuration. Verf.-Referat (gek.)