Myoelectric activity in four different shoulder muscles was collected and interpreted as indirect indicators of the load in eight different arm positions. The power spectrum changes associated with localized muscle fatigue were measured using a new dedicated instrument. Localized muscle fatigue was present in all muscles, in overhead and shoulder level work, and in some cases in waist level work #x2022; as well. For instance, in overhead work, the supraspinatus load was significantly affected by elbow positioning. The infraspinatus muscle held the highest fatigue effects of all muscles investigated. The results indicate the possibility of finding positions entailing reduction of the total muscular load in different working situations.
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