Morning Versus Afternoon Aerobic Exercise in Type 1 Diabetes

Aim. To determine whether the need for exogenous carbohydrate supplementation during exercise in type 1 diabetes is lower during morning exercise compared to afternoon exercise, and whether this is associated with greater lipid oxidation in the morning. Design and methods Twelve subjects with type 1 diabetes will participate in a randomized crossover study. Subjects will perform moderate intensity at 60% of VO2max for 1 hour during one morning (9 AM) and one afternoon (4 PM). Glucose monitoring will occur every 10 minutes during exercise, and every 5 minutes if blood glucose drops below 3.9 mmol/l. If blood glucose drops below 3.9 mmol/l, glucose infusion will be administered at a rate that keeps blood glucose just above 5 mmol/l. Glucose and palmitate tracers will be infused and indirect calorimetry will be used to assess glucose and lipid metabolism. Blood samples will be gathered to measure tracer levels, growth hormone, cortisol, and free fatty acids (FFA). Endpoints: Volume of intravenous glucose needed to maintain glucose above 5 mmol/l during the two exercise bouts, lipid- and carbohydrate oxidation rates, time to hypoglycemia, delta blood glucose levels, lipolysis rate, and endogenous glucose production.