Thus, both the contractile and transmission mechanism may be impaired by continuous muscle activity. The other activity constituted a diverting activity that produced the accelerated recovery of the central mechanism. It is explained as follows. During muscle fatigue, feedback of nerve impulses from the fatigued muscles impinges on a part of the reticular formation and causes an inhibition of voluntary effort. Diverting activity, on the other hand, produces an increased inflow of impulses from non-fatigued parts of the body to the facilitatory part of the reticular formation, thus shifting the balance between inhibition and facilitation in a facilitatory direction.
Central fatigue is also an expression of lowered arousal.
During fatigue studies, EEGs show a gradual appearance of the characteristic alpha-rhythm as fatigue progresses. The introduction of diverting activity makes the alpha-rhythm disappear. Alpha-rhythms are a signal of lowered arousal level in the brain, and usually are found when subjects close their eyes and disappear when the eyes are opened. The inhibition may act on the motor pathways anywhere from the voluntary centers in the brain to the spinal motor neurons. This kind of fatigue should manifest itself by a decrease in the outflow of motor impulses to the muscles.