During fatiguing contractions of muscles typical changes in the surface electromyogram (EMG) are found, like an increase in the EMG amplitude and a shift of the frequency spectrum towards lower values. Such changes can be used to indicate the occurrence of muscular fatigue. It has to be considered that EMG changes not only depend on muscular fatigue but also on the contraction force of the muscle under test. Suitable methods are shown which can, according to this condition, be applied for the determination of muscular fatigue occurring during occupational work.