Role of Central Fatigue in Resistance and Endurance Exercises: An Emphasis on Mechanisms and Potential Sites

Abstract

An exercise-induced reduction in maximal force production, or the inability to continue an activity with enough force, is defined as fatigue. Although the etiology of fatigue is complex, it can be divided into two distinct components: central and peripheral. Central fatigue is the progressive exerciseinduced loss of the voluntary activation, or decrease in the neural stimulation, of the muscle, thereby reducing maximal force production. Considering the different mechanisms of strength and endurance activities as well as previous research, the authors suggest that there is peripheral fatigue in both kinds of activities. However, the mechanisms of fatigue and the rate of perceived exertion are distinct (mentally, endurance exercise is more difficult). An analysis of fatigue kinetics shows that peripheral fatigue occurs initially, and the central nervous system tries to prevent the disorder via output force through the perceptions of the metabolic condition of the muscle and the activation of additional motor units. Once peripheral fatigue surpasses a certain amount, the central nervous system reduces the number of activated motor units to prevent serious disorders in homeostasis and muscle damage, and protects the central governor. Still, in important and critical situations such as the final stages of running a marathon (when the last flight of runners is observed) and fight-or-flight situations in which someone faces a worse outcome if a task is abandoned, humans can choose one of worse or the worst alternatives to write their final destiny.