EMG manifestations of muscle fatigue development during low-force work

135 General discussion In the general introduction, it was stated that occupational work often involves prolonged sustained low-force repetitive activities and a number of recent trends may further increase the prevalence of this type of work. Although force levels are relatively low, muscle fatigue or physiological signs of localized muscle fatigue may develop during low-intensity work. Localized muscle fatigue in the trapezius muscle may be a precursor of work-related upper extremity disorders and may reduce performance of employees. Localized muscle fatigue is usually defined as an exercise-induced decline in the maximal force or power capacity of the muscle (Bigland-Ritchie and Woods 1984). However, during low-force activities a reduction in force generating capacity does not necessarily occur while physiological changes affecting the capacity of the muscle do (e.g. Moussavi et al. 1989). To evaluate muscle fatigue electromyographic (EMG) indicators of fatigue are commonly used, i.e. a compression of the power spectrum towards lower frequencies accompanied by an increase in amplitude of the EMG signal (De Luca 1984, Basmajian and De Luca 1985).