Effect of Exercise Intensity on Exogenous Glucose Requirements to Maintain Stable Glycemia At High Insulin Levels in Type 1 Diabetes

CONTEXT: Under basal insulin levels, there is an inverted U relationship between exercise intensity and exogenous glucose requirements to maintain stable blood glucose levels in type 1 diabetes (T1D), with no glucose required for intense exercise (80% V̇O2 peak), implying that high-intensity exercise is not conducive to hypoglycemia. OBJECTIVE: This work aimed to test the hypothesis that a similar inverted U relationship exists under hyperinsulinemic conditions, with high-intensity aerobic exercise not being conducive to hypoglycemia. METHODS: Nine young adults with T1D (mean ± SD age, 22.6 ± 4.7 years; glycated hemoglobin, 61 ± 14 mmol/mol; body mass index, 24.0 ± 3.3 kg/m2, V̇O2 peak, 36.6 ± 8.0 mL·kg-1 min-1) underwent a hyperinsulinemic-euglycemic clamp to maintain stable glycemia (5-6 mmol·L-1), and exercised for 40 minutes at 4 intensities (35%, 50%, 65%, and 80% V̇O2peak) on separate days following a randomized counterbalanced study design. MAIN OUTCOME MEASURES: Glucose infusion rates (GIR) and glucoregulatory hormones levels were measured. RESULTS: The GIR (± SEM) to maintain euglycemia was 4.4 ± 0.4 mg·kg-1 min-1 prior to exercise, and increased significantly by 1.8 ± 0.4, 3.0 ± 0.4, 4.2 ± 0.7, and 3.5 ± 0.7 mg·kg-1 min-1 during exercise at 35%, 50%, 65%, and 80% V̇O2 peak, respectively, with no significant differences between the 2 highest exercise intensities (P > .05), despite differences in catecholamine levels (P < .05). During the 2-hour period after exercise at 65% and 80% V̇O2 peak, GIRs did not differ from those during exercise (P > .05). CONCLUSIONS: Under hyperinsulinemic conditions, the exogenous glucose requirements to maintain stable glycemia during and after exercise increase with exercise intensity then plateau with exercise performed at above moderate intensity ( > 65% V̇O2 peak). High-intensity exercise confers no protection against hypoglycemia.