Substrate utilization and glucose turnover during exercise of varying intensities in individuals with NIDDM

Purpose: This investigation was undertaken to examine substrate utilization and glucose turnover during exercise of varying intensities in NIDDM patie nts, Methods: Six male NIDDM patients (N) and six male controls (C) of simi lar age, body weight, % body fat, and (V) over dot O-2peak were studied in two experimental sessions administered in a randomized counterbalanced orde r. During each session the subjects cycled at a power output corresponding to 50% of (V) over dot O-2peak or 70% of (V) over dot O-2peak. 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 we re used to assess substrate utilization and glucose turnover during exercis e. Results: Rates of carbohydrate (CHO) and Lipid oxidation increased (P < 0.05) during both the 50% and 70% trials. Rates of CHO oxidation were great er (P ( 0.05) during the 70% than during the 50% trial. However, rates of l ipid oxidation were similar in the two trials. No differences in rates of C HO and Lipid oxidation were observed in N and C. Rates of hepatic glucose p roduction (R-a) and plasma glucose utilization (R-d) increased (P < 0.05) d uring exercise, and the increases were similar in the 50% and 70% trials. R -a did not differ between N and C. However, R-d was greater (P < 0.05) in N than in C. Plasma glucose concentration decreased (P < 0.05) in N, with th e decrease being similar in the 50% and 70% trials. In contrast, plasma glu cose concentration remained unchanged during both the 50% and 70% trials in C. Conclusions: Exercise results in a greater increase in plasma glucose u tilization 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 gl ucose utilization and plasma glucose concentrations are similar during exer cise of varying intensities. Despite a greater glucose utilization, carbohy drate and fat oxidation are similar in the two groups and their relations t o exercise intensity are not altered by NIDDM.