A24 Fatigue

Topic

In general, this type of sports-related fatigue represents a reversible reduction in an athlete's capacity to generate force or power during sustained exertion. Consequently, this fatigue comprises both a peripheral component—located within the muscle itself—and a central component, located within the central nervous system.

The peripheral component depletes the muscle's immediate energy substrates, leads to the accumulation of acidic metabolites within the muscle, and alters the function of the sarcoplasmic reticulum—the internal compartment responsible for releasing and resequestering the calcium required for muscle contraction.

This muscle fatigue reduces both the maximal force and the maximal shortening velocity defined by the Hill curve (a model describing muscle mechanics), thereby shifting the muscle's peak power output toward lower velocity and force values ​​on the curve. Further progression of this peripheral fatigue component causes a further reduction in the maximal force and maximal shortening velocity on the muscle's Hill curve.

The central component of this fatigue reduces the excitatory drive sent by the central nervous system to the athlete's motor neurons; this impairs proprioceptive capacity and neuromuscular control—factors linked to control failure in other models within this framework. A further reduction in this excitatory drive to the motor neurons increases the risk of injury, particularly toward the end of a training session or competition, when central fatigue has accumulated to its highest levels. Consequently, this model—which begins by accounting for a reversible reduction in the athlete's capacity—dictates that the athlete's ultimate performance evolves according to Banister’s fitness-fatigue model; this performance is represented as the difference between accumulated adaptation and accumulated fatigue over the course of a training period. The reversibility of this fatigue follows an exponential recovery pattern, with a much shorter time scale for acute fatigue than for chronic fatigue. If the athlete's accumulated fatigue is chronic in nature, the subsequent recovery—governed by this same exponential model—extends over an even longer time scale.

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