Mechanomyographic amplitude tracks fatigue-induced changes in mean power, but not moment production

BACKGROUND: It has been hypothesized [1] that the amplitude of the mechanomyographic (MMG) signal should track mean power output (MP) during dynamic muscle actions. Bodor's hypothesis has been supported in studies of non-fatigued muscles where MMG amplitude was shown to track velocity-related changes in MP, but not moment production, during concentric and eccentric muscle actions. OBJECTIVE: The purpose of this study was to further test the hypothesis of Bodor [1] by examining the patterns of MMG amplitude responses during a fatiguing workbout that included repetitions that were characterized by constant moment production, but decreasing MP. METHODS: Eleven subjects performed 50 submaximal (65% of peak moment), concentric, isokinetic, forearm flexion repetitions at 60 degrees/s. Polynomial regression analyses were used to examine the composite patterns of responses for moment, MP, and MMG amplitude from the biceps brachii across the fatiguing workbout. RESULTS: There were linear decreases across the repetitions for MP (r = 0.93) and MMG amplitude (r = 0.70), but no change in moment production. CONCLUSIONS: The current findings extend the hypothesis of Bodor [1] to the process of fatigue and suggested that MMG amplitude may be useful for monitoring decreases in MP during submaximal, fatiguing workbout where moment production is maintained.