Regeneration After Ultra-Endurance Exercise.

Most of the research on endurance exercise has focussed on the physiological and metabolic demands during an event and on factors causing fatigueFatigue during and after prolonged submaximal running may have many origins. The conventional explanation for fatigue after running a marathon or ultra-marathon is that glycogen is depleted in the skeletal muscles, thus reducing their ability to produce force. This form of fatigue may occur only when the muscle glycogen concentrations fall below a critical level perhaps causing impaired sarcoplasmic reticulum function. Fatigue, particularly after prolonged exercise exceeding 4 hours, may also coincide with the development of hypoglycaemia. There is some evidence to suggest that this fatigue may be delayed if carbohydrate is ingested during the event. The fatigue associated with hypoglycaemia probably has its origins in the central nervous system (CNS). Another mechanism underlying CNS fatigue after prolonged exercise proposed by Newsholme et al. (1992)} is that as the duration of exercise increases, more plasma free-tryptophan crosses the blood brain barrier and is converted into serotonin, which increases the perception of fatigue.Fatigue after prolonged exercise, particularly in hot, humid environments may also be caused by factors affecting the CNS arising from sustained elevation of muscle and possibly brain temperature . Studies have also identified a type of neuromuscular fatigue which occurs during and after a marathon and which accounts for the decrement in running performance. The above discussion highlights some of the metabolic issues and aetiology of fatigue associated with prolonged submaximal exercise. [ABSTRACT FROM AUTHOR]