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The effect of Hyperglycemia on Carbohydrate Metabolism During Prolonged Intense Exercise

In the present study the effects of hyperglycemia (i.e.,12 mmol/l) throughout prolonged intense exercise on carbohydrate metabolism were examined. Eight male subjects undertook two trials during which they exercised on a cycle ergometer at an intensity of -70% Vozmax for 120 min. In the first trial (trial A), subjects had their blood glucose concentration clamped at 12 mmol/l, 30 min before exercise and throughout exercise, The same rate and volume of infusion of 0.9% saline as had occurred for trial A were used in a placebo trial (trial B). Calculted of the rates of total carbohydrate oxidation showed that trial A resulted in significantly higher values when compared with trial B (P<0.01), and the maximal rates of glucose infusion varied between 1.33 and 2.78 g/min at 100-120 min. Musccleglycogen concentrations were significantly depleted (P<0.01) after both trials (170 vs. 206/ molt dry Wt.). This apparent difference between two trials may be accounted for by storage of 22.6g glucose during the 30-min prime infusion. The results of this study confirm that maintained hyperglycemia promotes carbohydrate oxidation and glucose uptake, and it does not effect sparing muscle glycogne. However hyperglycemia may spare other carbohydrate sources, especially hepatic reservoirs.