Electromyographic signs of shoulder muscle fatigue in repetitive arm work paced by the Methods-Time Measurement system.

Surface electromyographic (EMG) recordings from the lateral and cervical portions of the descending trapezius muscle and from the infraspinatus muscle were assessed for six female subjects performing a standardized repetitive work simulation task for 1 h. The work pace was determined according to the Methods-Time Measurement system to 2466 cycles.h-1. The variation in load levels were high and indicated dynamic muscle activity. A decrease in the EMG mean power frequency and an increase in the root-mean-square amplitudes, both indicating muscle fatigue, developed in all muscles of most of the subjects. EMG signs of fatigue, analyzed separately for each 5-min period, showed variable fatigue patterns both between muscles and between subjects. It is therefore suggested that dynamic work movements do not protect the muscles of the shoulder and neck from fatiguing processes in highly repetitive work with short cycle times.