Development and evaluation of an observational method for quantifying exposure to hand activity and other physical stressors in manual work.

Abstract

An observational method was developed in which hand activity/repetition and other physical stressors associated with work related musculoskeletal disorders (WRMSDs) are rated on scales from 0-10. A series of evaluations was performed to determine the method's reliability, internal validity, and external validity. The ratings of repetition were moderately correlated with measures of number of exertions per unit time and the amount of recovery time within the job cycle. Cycle time was not related to the analyst ratings. An analysis of test-retest reliability over a 1 1/2 to 2 year time period revealed a high level of consistency. Twelve jobs were analyzed by four groups of raters to determine inter-rater reliability. There was more variability in the initial ratings (between individuals) than in the final ratings (between groups). Repetition exhibited very strong agreement between raters. A laboratory study was conducted to assess the internal validity of the method. Instrumental measurements of muscle activity and wrist position were compared with ratings of equivalent parameters. When repetition rating was modeled as a function of movement speed and exertion time, both terms were significant and the model explained 88% of the variability in the repetition ratings. For both posture and force, there were significant relationships between the measures obtained from the instrumentation and the ratings $\rm(0.28<r\sp2<0.54).$ An epidemiological study was conducted which evaluated the relationship between repetitive work and prevalence of various WRMSDs in workers. Repetition was associated with reports of general discomfort (OR = 1.17 for 1 unit increase in repetition), tendinitis (OR = 1.21), and symptoms consistent with Carpal Tunnel Syndrome (CTS) (OR = 1.16). There was borderline significance for the relationship between repetition and CTS diagnosis based on the combination of symptoms and electrophysiological testing (OR = 1.22). The method for rating repetition exhibited high levels of reliability and validity. Repetition levels were found to be positively associated with risk of upper limb discomfort, tendinitis, and Carpal Tunnel Syndrome. The rating scales for the other stressors have varying levels of reliability and validity.