Myoelectrical manifestations of localized muscular fatigue in humans.

Fatigue may be described as the decline in the ability of an individual to maintain a level of performance. However, the issue of fatigue in man is complex due to the various physiological and psychological phenomena which contribute to it. This article is limited to a discussion appertaining to that fatigue associated with changes in the physiological processes, and specifically that which is caused by sustained or repeated muscle contractions. It has long been known that during muscle contractions the frequency spectrum of the myoelectric signal undergoes a shift. Recently, several analyses and investigations have been reported on the applicability of this phenomenon for supplying objective or noninvasive measurements of localized muscle fatigue. The essence and results of pertinent publications are discussed with emphasis on the relationship between the spectral shift of the myoelectric signal, conduction velocity of muscle fibers, pH of the interstitial fluid and blood flow within a muscle.