The importance of the work/rest pattern as a risk factor in repetitive monotonous work.

The work cycle time is an important parameter in assessing the risk for development of musculoskeletal disorders caused by repetitive monotonous work. The work/rest pattern in the work cycle time may be an even more important factor. Based on the normalized work cycle time for 48 meat cutters, a "slow" group (121.0-138.9% of the mean work time) and a "fast" group (68.4-85.5% of the mean work time) were defined. During work, the mean muscle activity level for the wrist extensor was 20% of the reference value, and the flexor muscles were 40% of the reference value. No differences were observed between the "slow" and the "fast" group of meat cutters. Electrophysiological signs of muscle fatigue in the power spectrum analysis from the EMG signals registered during meat cutting showed no differences between the groups. Meat cutting work seems to be performed with a stereotyped muscle activity pattern with only small variations for the forearm muscles. Regardless of a rather large difference in the work/rest pattern between the two groups of meat cutters, no differences were found in any of the measured acute physiological responses. To evaluate the risk of the workload, more comprehensive variables must be included in addition to the work cycle time and the work/rest pattern. Relevance to industry One explanation for the high frequencies of musculoskeletal disorders has been suggested to be the speed of work. A way to estimate the speed of work is to measure the work cycle time and the work/rest pattern. The purpose of this study is to evaluate the work/rest pattern as a risk factor. (C) 2000 Elsevier Science B.V. All rights reserved.