Mediating effects of wrist reaction torque on grip force production

Abstract

A pistol grip, power tool simulator was developed and used to examine the mediating effects of wrist reaction torque on changes in direct measures of grip force. The effects of thrust force (0 and 45 N), and pre-existing grip force (10 and 30% MVC) were also controlled with this simulator. A modified Jamar dynamometer attached to the motor shaft, permitted grip forces to be measured directly. A 2×2×2×2, repeated measures ANOVA, was used to test the effects of torque impulse magnitude, duration, thrust force, and pre-existing grip force on changes in normalized grip force. Subjects included 11 males and 8 females. Grip force increased significantly (31–254%) with increasing torque magnitude. Grip force decreased (15–37%) with increasing pre-torque grip force. Grip force was not significantly affected by torque duration. Grip force also decreased 10–31% with increasing thrust force. Derived measures of hand-wrist dynamic compliance decreased significantly with increases in torque duration, thrust force, torque magnitude, and pre-torque grip force. The wrist actively stiffened under these conditions. Relevance to industry Manufacturers of powered hand tools may find this study useful to further their understanding of the effects of tool use on the hand–wrist system. The importance of torque shut-off mechanisms and a continued attention to optimal handle design is also supported by this work.