UTILIZATION OF GLYCOGEN BUT NOT PLASMA-GLUCOSE IS REDUCED IN INDIVIDUALS WITH NIDDM DURING MILD-INTENSITY EXERCISE

To test the hypothesis that substrate utilization during mild-intensit y exercise differs in non-insulin-dependent diabetes mellitus (NIDDM) compared with nondiabetic subjects, seven lean healthy subjects (L), s even obese healthy subjects (O), and seven individuals with NIDDM were studied during 40 min of mild-intensity cycling (40% of peak O-2 upta ke). Systemic utilization of plasma glucose (Glc Rd) was determined by using isotope dilution methods. Gas exchange was measured to determin e rates of carbohydrate (CHO) and lipid oxidation. During exercise, wh en CHO oxidation was greater than Glc Rd, the net oxidation of glycoge n was calculated as the difference: CHO oxidation - Glc Rd. During mil d-intensity cycling, the respiratory exchange ratio was similar across groups (0.87 +/- 0.02, 0.85 +/- 0.02, and 0.86 +/- 0.01 in L, O, and NIDDM subjects, respectively), and CHO oxidation accounted for one-hal f of total energy expenditure during exercise. Glc Rd increased during exercise and was greatest in subjects with NIDDM (3.0 +/- 0.2, 2.9 +/ - 0.2, and 4.5 +/- 0.4 ml . kg(-1). min(-1) in L, O, and NIDDM subject s, respectively, P < 0.05), yet Glc Rd was less than CHO oxidation dur ing exercise, indicating net oxidation of glycogen. Glycogen oxidation was greater in L and O than in NIDDM subjects (3.4 +/- 1.0, 2.5 +/- 0 .9, and 1.7 +/- 0.8 ml . kg(-1). min(-1); P < 0.05). In summary, durin g mild-intensity exercise, NIDDM subjects have an increased Glc Rd and a decreased oxidation of muscle glycogen.