The Biochemistry of Human Energy Systems

4The ingestion of glucose or carbohydrates during exercise can marginally prolong performance. It has no effect on muscle glycogen but it does spare the use of liver glycogen if it can be assimilated into the circulatory system in time. The rate of emptying from the stomach and absorption into the blood stream determine the value of this supplement. Emptying is facilitated by the glucose being diluted as a cool drink taken in resting or calm circumstances.
5The rate of muscle glycogen use appears to be increased in hot conditions.
6However the body's athletic conditioning also plays a role in what fuel is chosen. Firstly specific training can be done to increase the creatine system and also to condition the muscles to resist the effects of lactic acid build-up from the glycolytic system. In addition as specific athletic fitness alters the call on fat versus carbohydrate oxidation and glycogen depletion is stalled, 2Foster & Costill (1978). In addition regular training increases the total number of mitochondria in the muscles, thus making the 'battery' they provide larger, this not only improves endurance, 12Holloszy (1975) but delays the need to switch to fat, 13Holloszy (1967) and 14Dudley (1975), making muscle more efficient at a given intensity.
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