Reproducibility of the mean power frequency of the surface electromyogram

There is evidence in the literature that the decrease of mean power frequency (MPF) during exercise is greater as a muscle become more fatigued. After strenuous exercise this phenomenon can last several days. It is usually assumed, however, that the MPF has a good reproducibility. In this study the reproducibility of the MPF of the surface electromyogram of the biceps brachii muscle was investigated for five subjects on 5 successive days. Force level, muscle length and skin temperature were kept constant. The results show that interindividual differences in MPF were large (SD 11.5 Hz). However, during these 5 days, the range in MPF for individual subjects was small. The SD of the trials within subjects and days was 2.0 Hz, while the SD trials excluded). It is hypothesized that this SD may be due to variations in the electrode replacement. It is concluded that the variability in MPF for a subject is small compared to the decrease of the MPF associated with muscle fatigue and which can therefore be determined reliably during longitudinal studies.