KEY POINTS
– Prolonged strenuous exercise increases plasma concentrations of the hormones epinephrine, growth hormone, cortisol, and glucagon. Insulin is decreased.
– Ingestion of carbohydrate during prolonged exercise blunts these hormone responses and delays fatigue.
– The blunted hormone response may contribute to a delay in both central (brain) and peripheral (muscle) fatigue by helping to spare liver and muscle glycogen, maintain blood glucose, and reduce blood concentrations of free fatty acids, free tryptophan, and ammonia.
– To prevent a fall in blood glucose concentration and to blunt the hormonal response to exercise, every 15-20 min athletes should drink 8-12 oz (240-350 ml) of a sports drink that contains carbohydrate.

INTRODUCTION
The endocrine (hormonal) system provides for normal bodily functions, including the maintenance of blood glucose levels for optimal health and exercise performance. A decrease in blood glucose during prolonged strenuous exercise can be a major contributor to the onset of fatigue (Davis & Fitts, 1998). The endocrine system attempts to maintain adequate blood glucose levels during exercise by mobilizing other fuels for energy and by stimulating production of glucose from amino acids and other non-carbohydrate sources. Unfortunately, these responses can only delay depletion of the body’s carbohydrate stores, and fatigue can occur in spite of large increases in  irculating hormones.
In fact, as will be described later, there is some evidence suggesting that the dramatic increase in stress hormones that accompany strenuous exercise may actually hasten fatigue.
Ingesting properly formulated carbohydrate drinks can delay fatigue by keeping blood glucose at high levels (Coggan & Coyle, 1987) and perhaps by sparing muscle glycogen stores (Hargreaves, 2000). Interestingly, the  increase in stress-related hormones during exercise is also attenuated when carbohydrate drinks are ingested, but whether this has any bearing on the delay of fatigue is uncertain. Therefore, the purpose of this paper is to briefly review how the glucoregulatory hormones (epinephrine, cortisol, insulin, glucagon, and growth hormone) respond to exercise, how carbohydrate feeding alters these responses, and to judge whether there is an association between
altered hormone responses and postponement of fatigue.

FULL ARTICLE IN PDF: http://www.jbc.org/content/251/23/7494.full.pdf

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