Utilization of glycogen but not plasma glucose is reduced in individuals with NIDDM during mild-intensity exercise

Colberg, Sheri R., James M. Hagberg, Steve D. McCole, JosephM. Zmuda, Paul D. Thompson, and David E. Kelley. Utilization ofglycogen but not plasma glucose is reduced in individuals with NIDDMduring mild-intensity exercise. J. Appl.Physiol. 81(4): 2027-2033, 1996.To test thehypothesis that substrate utilization during mild-intensity exercisediffers in non-insulin-dependent diabetes mellitus (NIDDM) comparedwith nondiabetic subjects, seven lean healthy subjects (L), seven obesehealthy subjects (O), and seven individuals with NIDDM were studiedduring 40 min of mild-intensity cycling (40% of peakO₂ uptake). Systemic utilization of plasma glucose (Glc Rd) was determined by using isotope dilution methods. Gas exchange was measured to determine rates of carbohydrate (CHO) and lipid oxidation. During exercise, when CHOoxidation was greater than Glc Rd, the net oxidation of glycogen wascalculated as the difference: CHO oxidation  Glc Rd. Duringmild-intensity cycling, the respiratory exchange ratio was similaracross groups (0.87 ± 0.02, 0.85 ± 0.02, and 0.86 ± 0.01 inL, O, and NIDDM subjects, respectively), and CHO oxidation accountedfor one-half of total energy expenditure during exercise. Glc Rdincreased 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 ·} min¹in L, O, and NIDDM subjects, respectively,P < 0.05), yet Glc Rd wasless than CHO oxidation during exercise, indicating net oxidation ofglycogen. Glycogen oxidation was greater in L and O than in NIDDMsubjects (3.4 ± 1.0, 2.5 ± 0.9, and 1.7 ± 0.8 ml ^· kg^{1 ·} min¹;P < 0.05). In summary, duringmild-intensity exercise, NIDDM subjects have an increased Glc Rd and adecreased oxidation of muscle glycogen.