International Journal of Industrial Ergonomics 25 (2000) 367}373 The importance of the work/rest pattern as a risk factor in repetitive monotonous work. Hanne Christensen Ph.D., Karen S+gaard Ph.D., Marianne Pilegaard M.Sc., Henrik B. Olsen Engineer Department of Physiology, National Institute of Occupational Health, Lers~ Parkalle & 105, DK-2100, Copenhagen, Denmark Received 28 January 1998; accepted 24 May 1999 Abstract 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 `slowa group (121.0}138.9% of the mean work time) and a `fasta group (68.4}85.5% of the mean work time) were de"ned. During work, the mean muscle activity level for the wrist extensor was 20% of the reference value, and the #exor muscles were 40% of the reference value. No di!erences were observed between the `slowa and the `fasta group of meat cutters. Electrophysiological signs of muscle fatigue in the power spectrum analysis from the EMG signals registered during meat cutting showed no di!erences 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 di!erence in the work/rest pattern between the two groups of meat cutters, no di!erences 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.  2000 Elsevier Science B.V. All rights reserved. Keywords: Meat cutters; Muscle fatigue; Work/rest pattern; Work cycle time; EMG; Forearm muscles 1. Introduction The slaughterhouse industry today has a high level of technology and many work processes are semiautomized. Facilities to decrease the amount of manual handling have been introduced during the last years. However there are still some pro- cesses, such as meat cutting, where attempts to automation have not been successful. The quality of the "nal product, such as a deboned piece of meat, is still better when a human hand has performed the process (Fig. 1), than a machine. A very high frequency of selfreported troubles in the upper extremities is observed in the slaugh- terhouse industry, particularly among the meat cutters. 0169-8141/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 8 1 4 1 ( 9 9 ) 0 0 0 2 5 - 6