The influence of wrist position on individual finger forces during forceful grip.

Nine healthy subjects sustained maximum grip of an instrumented handle while voluntarily moving the wrist joint within their available range of motion of the wrist in a continuous and random manner. Individual finger forces and wrist angular positions in flexion/extension and radial/ulnar deviation were recorded simultaneously. Wrist position had a significant effect on individual finger force and total force production. Peak finger forces were produced at 20 degrees of wrist extension and 5 degrees of ulnar deviation. At this position, a mean total grip force of 114.9 (+/-12.8) N was produced with force-sharing percentages of 32.2% (+/-3.8%), 32.6% (+/-4.3%), 23.5% (+/-4.5%), and 11.7% (+/-4.9%) among the index, middle, ring, and small finger, respectively. As the wrist was moved farther away from this position, the forces produced by individual fingers decreased incrementally; however, the decreases in individual finger forces were not proportional, leading to a dependence of finger force-sharing patterns on wrist position.