UBC Theses and Dissertations
Glycogen utilization in the athlete under conditions of accute, moderate hypoxia Hazlett, David Lorne
It is common knowledge that diet and endurance training both have a major impact on body glycogen stores and carbohydrate metabolism. Usual nutritional recommendations for athletes participating in endurance activities are to consume at least 8 grams of carbohydrate per kilogram body weight. This level of carbohydrate intake has been found to optimally maintain muscle glycogen stores in actively training endurance athletes. This recommendation has been based on athletic activity undertaken under sea level conditions. A survey of the literature shows that this recommendation has never been investigated in athletes exercising under hypoxic conditions such as at altitude. Theoretical and experimental evidence would predict that under hypoxic conditions, one strategy which could maintain ATP production in the face of decreased oxygen availability is to increase flux through the glycolytic pathway. Increased glycolytic flux could ultimately affect carbohydrate use which could in turn lead to enhanced muscle glycogen use. If this did occur, it could have implications for dietary advice given to athletes exercising at altitude. It was our intent to see if these alterations occur with exercise under acute exposure to moderate altitudes such as those an athlete could conceivably face during competition. To investigate this possibility, muscle glycogen utilization was assessed during exercise at sea level (SL) and with acute exposure to simulated altitude (ALT) equivalent to 7500 feet above sea level. Six endurance trained cyclists exercised for 75 minutes at the same relative exercise intensity (65% of VO2 ma x) under each condition. In addition to glycogen use, plasma lactate serum glucose, and respiratory exchange ratios (RER) were also evaluated to assess whether any shift in substrate use occurred between conditions. There was a trend towards decreased muscle glycogen use under ALT conditions, however the difference was not found to be significant (P=0.09). Plasma lactate, serum glucose, and RER findings were also found to be not significantly different between conditions. This data suggests that exercise at the same relative intensity at ALT as SL does not result in enhanced carbohydrate use. From this it is inferred that under the conditions used, oxygen supply to exercising muscle is not diminished. These findings also suggest that in highly trained cyclists undertaking exercise under moderate altitude conditions, no increase in carbohydrate intake is necessary above that recommended for exercise of equivalent intensity at sea level.
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