Patterns of electromyographic shoulder muscle fatigue during MTM-paced repetitive arm work with and without pauses

Surface electromyographic recordings from the lateral and the cervical portions of the descending trapezius muscle and from the infraspinatus muscle were assessed for 12 female subjects during performance of a standardized repetitive work simulation task involving 1 h of continuous work and 1 h with introduced pause activities. Discomfort ratings and ratings of perceived exertion were also assessed. Work pace was determined according to MTM-110 (Methods-Time Measurement) as 2466 cycles for both working hours. Muscle fatigue with a decrease in the mean power frequency and an increase in root mean square amplitudes was found both during continuous work and during work with pause activities. The muscle fatigue was less pronounced when pause activities were introduced into the work. Five-minute fatigue patterns were lower during the second hour, indicating adaptation to the work task and work pace. The ratings of perceived exertion and discomfort were similar during work with and without pauses and were higher during the second hour of work. Both work pace and a varied muscle activity pattern are of importance for prevention of muscle fatigue.