Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Hence, maximal voluntary strength can often be below true maximal muscle force. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Evidence for "central" fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it.
It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force.
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