Psychophysically determined work-cycle parameters for repetitive hand gripping

Abstract

Carpal tunnel syndrome (CTS) and other cumulative trauma disorders (CTD's) are responsible for a high cost to the industry. CTS and CTD's have been reported in many industries and their risk factors have been identified. CTD occupational risk factors include repetitive movement, forceful exertions, sustained or constrained postures, vibration, low temperature, and mechanical stress. Exertion period and work duration have also been reported as risk factors. The literature search revealed the need for analytical studies of work cycle parameters, and the need to determine empirically the safety exposure limits for these factors. Therefore this study was concerned with presenting an analysis and definition of the work cycle parameters and investigating the safety exposure limits of the work cycle parameters. The psychophysical adjustment method was used to investigate the effect of force, wrist angle, and exertion period on the maximum acceptable work cycle parameters. The work cycle parameters were defined using the engineering definitions and terminology. These parameters were the rest period, duty cycle, and rest-to-work ratio. Twelve female subjects participated in a 40-minute hand gripping task and were allowed to adjust their rest period in relation to a set exertion period. ANOVA showed that there were significant effects of force, wrist angle, exertion period, and their interaction on rest period, duty cycle, and rest-to-work ratio atα = 0.001. Regression analysis was used to develop prediction models for the rest period, duty cycle, and rest-to-work ratio as a function of anthropometric dimensions of the hand and wrist, age, force, wrist angle, exertion period, maximum voluntary contraction (MVC), maximum deviation angle (MDA), and the percentage of MVC. The results of the regression analysis indicated that anthropometric dimensions and age were not significant factors. Relevance to industry Several countries have initiated prevention programs to control the prevalence of CTD's and CTS in the workplace. An important ingredient of these programs is designing the workcycle to provide adequate recovery time. This paper presents an analysis and prediction equations of the workcycle parameters for different work and task conditions.