DEVELOPMENT AND EVALUATION OF AN OBSERVATIONAL METHOD FOR ASSESSING REPETITION IN HAND TASKS

Several physical stressors, including repetitive, sustained, and force ful exertions, awkward postures, localized mechanical stress, highly d ynamic movements, exposures to low temperatures, and vibration have be en linked to increased risk of work-related musculoskeletal disorders. Repetitive exertions have been among the most widely studied of these stressors, but there is no single metric for assessing exposure to re petitive work. A new methodology enables repetitive hand activity to b e rated based on observable characteristics of manual work. This metho d uses a series of 10-cm visual-analog scales with verbal anchors and benchmark examples. Ratings for repetition reflect bath the dynamic as pect of hand movements and the amount of recovery or idle hand time. T rained jab analysis experts rate the jobs individually and then agree on ratings. For a group of 33 jobs, repetition ratings using this syst em were compared to measurements of recovery time within the cycle, ex ertion counts, and cycle time. Amount of recovery time within the job cycle was found to be significantly correlated with the analysis ratin gs (r(2)=0.58), as were the number of exertions per second (r(2)=0.53) . Cycle time was not related to the analyst ratings. Repeated analyses using the new method were performed 1 1/2 to 2 years apart on the sam e jobs with the same group of raters. Ratings for repetition differed less than 1 point (on the 10-cm scale), on average, among the differen t sessions,These results indicate that the method is sensitive to exer tion level and recovery time, and that the decision criteria and bench mark examples allow for a consistent application of these methods over a period of time. This method of rating repetition can be combined wi th similar scales for other physical stressors.