Wrist Motions in Industry: Variance between Jobs and Subjects

Abstract

Ergonomists assume that they can design out injurious postures and motions with engineering controls by guiding the worker to use the preferred, less injurious motions. The variance between workers performing tasks in ergonomically-designed jobs is assumed to be dominated by the variance between jobs. However, little research exists that quantified whether this assumption is valid.

The present study examined the wrist motions of 40 industrial workers who performed highly repetitive, hand-intensive jobs of low and high risk of cumulative trauma disorders (CTDs). The position and angular velocity and acceleration of these workers' wrists were measured in all three planes (radial/ulnar, flexion/extension, pronation/supination) with goniometry. The results of this study show that for all the kinematic variables, the variance between subjects within jobs accounted for a substantial, and often majority, amount of variance. The results of this study demonstrate that ergonomists should consider the variability in motion patterns between workers when designing existing or new jobs and also should monitor at least two subjects per job in quantitative surveillance studies of wrist motion.