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: 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±4.7y; glycated hemoglobin, 61±14mmol·mol -1; body mass index, 24.0±3.3kg·m -2, V̇O2 peak, 36.6±8.0ml·kg -1min -1) were subjected to a hyperinsulinemic-euglycemic clamp to maintain stable glycemia (5-6mmol·L -1), and exercised for 40 min at 4 different 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.

RESULTS: The GIR (±SEM) to maintain euglycemia was 4.4±0.4mg·kg -1min -1 prior to exercise, and increased significantly by 1.8±0.4, 3.0±0.4, 4.2±0.7, and 3.5±0.7mg·kg -1min -1 during exercise at 35, 50, 65, and 80% V̇O2 peak, respectively, with no significant differences between the two highest exercise intensities (p>0.05), despite differences in catecholamine levels (p<0.05). During the 2-h period after exercise at 65 and 80% V̇O2 peak, GIRs did not differ from those during exercise (p>0.05).

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.