Invited Review : Exercise and Central Fatigue

Journal of Exercise Nutrition & Biochemistry 2003;7(3):227-234.

Abstract

When we exercise, we feel fatigue at a certain point during exercise. Because the manifestation of feeling of fatigue occurs far before physical exhaustion, it can be thought as a kind of defense system of the body. This feeling of fatigue seems to be generated by central nervous system, and can be designated as central nervous system (CNS) fatigue, however, its exact mechanism remains elusive. Some theories has been proposed to explain the mechanism so far. In this review such theories conceming serotonin, ammonia and cytokines mentioned. TGF-B from among those cytokines, is commented in detail. The concentration of serotonin in the brain increases during endurance exercise. This seemed to lead the activation of serotonergic nervous system and the emergence of CNS fatigue. Ammonia is mainly produced by AMP degradation in skeletal muscles and affects neurons. Various cytokines are supposed to relate with CNS fatigue because those used as therapeutics caused feeling of tiredness as a side effer and the concentrations of some of those in plasma increased in acute physical exercise. The concentration of TGF-B in the brain increased during exercise and it was suggested to directly act on neurons. TGF-B administered into the brain seemed to generate feeling of fatigue and to cause the depression of spontaneous motor activity.

Key Words: Fatigue, serotonin, tryptophan, BCAA, ammonia, cytokine, TGF-β