Substrate source utilization during moderate intensity exercise with glucose ingestion in Type 1 diabetic patients

Substrate oxidation and the respective contributions of exogenous glucose, glucose released from the liver, and muscle glycogen oxida-tion were measured by indirect respiratory calorimetry combined with tracer technique in eight control subjects and eight diabetic patients (5 men and 3 women in both groups) of similar age, height, body mass, and maximal oxygen uptake, over a 60-min exercise period on cycle ergometer at 50.8 % (SD 4.0) maximal oxygen uptake [131.0 W (SD 38.2)]. The subjects and patients ingested a breakfast (containing 80 g of carbohydrates) 3 h before and 30 g of glucose (labeled with 13C) 15 min before the beginning of exercise. The diabetic patients also received their usual insulin dose [Humalog 9.1 U (SD 0.9); Humulin N 13.9 U (SD 4.4)] immediately before the breakfast. Over the last 30 min of exercise, the oxidation of carbohydrate [1.32 g/min (SD 0.48) and 1.42 g/min (SD 0.63)] and fat [0.33 g/min (SD 0.10) and 0.30 g/min (SD 0.10)] and their contribution to the energ