Suiface electromyography (SEMG) is widely used in the study of localized muscle fatigue because many characteristics of the SEMG signal correlate with the physiological processes related to fatigue, such as conduction velocity of the motor unit action potentials (MUAP), synchronization of the motor units (MU), and recruitment patimis to name a few. However the traditional method of analyzing the SEMG signal in terms of fatigue (spectral method) requires stationarity of the process. In this study, a new method of analyzing the SEMG signal based on non-linear time series analysis was suggested and tested for two different types of fatiguing contractions of the elbow flexors. The effects of fatiguing exercise on motor control performance of the upper extremities was also investigated.

Our results indicate that the non-linear method is sensitive to different changes of the SEMG signal than the spectral methods and that its applicability depends on the type of contraction. The non-linear method appears to be sensitive to central fatigue factors and it can be used in conjunction with the spectral methods in sustained maximal efforts. Also significant changes on the motor control performance of upper extremities were obsCTved as a consequence of local fatigue.