EMG-based detection of muscle fatigue during low-level isometric contraction by recurrence quantification analysis and monopolar configuration

The center frequency (CF) of the power spectral density of a bipolar-configured surface electromyogram is typically used as an index of muscle fatigue. However, this index may be inadequate for measuring wave slowing due to muscle fatigue during low-level contractions. A previous study in which strong muscle fatigue was mimicked by compressing the proximal region of the forearm during isometric contractions showed that the differences in the degree of fatigue under compression and non-compression conditions were undetectable. The purpose of this study was to improve detection sensitivity of surface EMG variation caused by muscle fatigue using two approaches. The first approach employed recurrence quantification analysis (RQA) instead of traditional frequency analysis (FA) to compute the muscle fatigue index. The second approach employed a monopolar configuration for measuring surface EMG. We measured the surface EMG signal by using monopolar and bipolar configurations simultaneously during low-level isometric contractions under blood flow-restricted (BFR) and unrestricted (CON) conditions, and then compared and evaluated the detected differences in muscle fatigue. The results showed that the effect of BFR was better detected by RQA than by FA, and that the fatigability change was larger in the monopolar configuration than in the bipolar configuration.