Evaluation of psychometric estimates of vibratory hand-tool grip and push forces

Tool grip and push forces are important determinants of health risk associated with operation of powered hand tools. In the field, use of sophisticated hand-force instrumentation can be impractical. This study investigated the potential for using psychophysical force recall methods to estimate grip and push forces when operating vibratory hand tools. This study examined various combinations of handle vibration and grip and push force exposures upon one's ability to recall those forces using psychophysical methods. Twelve male subjects grasped and pushed an instrumented handle for 45 s at one of three levels of force while it vibrated sinusoidally at one of five frequencies (0, 12.5, 40, 125, or 250 Hz). We examined the effects of post-exertion rest periods of 10 and 20 s upon force recall performance, and day-to-day test-retest reliability. Results showed vibration frequency and force level differentially influenced grip and push force recall accuracy. Subjects characteristically overestimated grip and push forces; especially during vibration exposures of 40 and 125 Hz. The magnitude of the overestimations increased as target force levels decreased. Test–retest correlations were reasonably strong.Relevance to industryOperators of powered hand tools are at risk of developing health problems associated with repeated forceful actions and exposure to intense hand-transmitted vibration. To better assess health risks, hand-tool coupling forces should be quantified. Psychophysical force recall techniques may permit assessment of these forces without the need for expensive or fragile instrumentation. An understanding of the effects of vibration and force level upon force recall accuracy and reliability must first be explored before such methods are proposed for research or field assessments.