Neuromuscular fatigue in healthy muscle: Underlying factors and adaptation mechanisms

Abstract

OBJECTIVES This review aims to define the concept of neuromuscular fatigue and to present the current knowledge of the central and peripheral factors at the origin of this phenomenon. This review also addresses the literature that focuses on the mechanisms responsible for the adaption to neuromuscular fatigue. METHOD One hundred and eighty-two articles indexed in PubMed (1954-2010) have been considered. RESULTS Neuromuscular fatigue has central and peripheral origins. Central fatigue, preponderant during long-duration, low-intensity exercises, may involve a drop in the central command (motor, cortex, motoneurons) elicited by the activity of cerebral neurotransmitters and muscular afferent fibers. Peripheral fatigue, associated with an impairment of the mechanisms from excitation to muscle contraction, may be induced by a perturbation of the calcium ion movements, an accumulation of phosphate, and/or a decrease of the adenosine triphosphate stores. To compensate for the consequent drop in force production, the organism develops several adaptation mechanisms notably implicating motor units. CONCLUSION Fatigue onset is associated with an alteration of the mechanisms involved in force production. Then, the interaction between central and peripheral mechanisms leads to a series of events that ultimately contribute to the observed decrease in force production.