Substrate utilization and glucose turnover during exercise of varying intensities in individuals with NIDDM. Med. Sci. Sports Exerc., Vol. 31, No. 1, pp. 82-89, 1999.
Purpose: This investigation was undertaken to examine substrate utilization and glucose turnover during exercise of varying intensities in NIDDM patients.
Methods: Six male NIDDM patients (N) and six male controls (C) of similar age, body weight, % body fat, and V˙O2peak were studied in two experimental sessions administered in a randomized counterbalanced order. During each session the subjects cycled at a power output corresponding to 50% of V˙O2peak or 70% of V˙O2peak. Duration of exercise was adjusted so that energy expenditure (EE) was equal in both the 50% and 70% trials. Isotope infusion technique and indirect calorimetry were used to assess substrate utilization and glucose turnover during exercise.
Results: Rates of carbohydrate (CHO) and lipid oxidation increased (P < 0.05) during both the 50% and 70% trials. Rates of CHO oxidation were greater (P < 0.05) during the 70% than during the 50% trial. However, rates of lipid oxidation were similar in the two trials. No differences in rates of CHO and lipid oxidation were observed in N and C. Rates of hepatic glucose production (Ra) and plasma glucose utilization (Rd) increased (P < 0.05) during exercise, and the increases were similar in the 50% and 70% trials. Ra did not differ between N and C. However, Rd was greater (P < 0.05) in N than in C. Plasma glucose concentration decreased (P < 0.05) in N, with the decrease being similar in the 50% and 70% trials. In contrast, plasma glucose concentration remained unchanged during both the 50% and 70% trials in C.
Conclusions: Exercise results in a greater increase in plasma glucose utilization in patients with NIDDM compared with that in normal individuals, and this increase mediates the decline in plasma glucose concentrations in patients with NIDDM. Under isocaloric conditions, the changes in plasma glucose utilization and plasma glucose concentrations are similar during exercise of varying intensities. Despite a greater glucose utilization, carbohydrate and fat oxidation are similar in the two groups and their relations to exercise intensity are not altered by NIDDM.