Continuous glucose monitoring reveals delayed nocturnal hypoglycemia after intermittent high-intensity exercise in nontrained patients with type 1 Diabetes

Objective: Exercise is a cornerstone of diabetes therapy in type 1 diabetes mellitus (DMT1) patients. The type of exercise is important in determining the propensity to hypoglycemia. We assessed, by continuous glucose monitoring (CGM), the glucose profiles during and in the following 20 h after a session of two different types of exercise. Research Design and Methods: Eight male volunteers with well-controlled DMT1 were studied. They underwent 30 min of both intermittent high-intensity exercise (IHE) and moderate-intensity exercise (MOD) in random order. Expired air was recorded during exercise, while metabolic and hormonal determinations were performed before and for 120 min after exercises. The CGM system and activity monitor were applied for the subsequent 20 h. Results: Blood glucose level declined during both type of exercise. At 150 min following the start of exercise, plasma glucose content was slightly higher after IHE. No changes were observed in plasma insulin concentration. A significant increase of norepinephrine concentration was noticed during IHE. Between midnight and 6:00 a.m. the glucose levels were significantly lower after IHE than those observed after MOD (area under the curve, 23.3 ± 3 vs. 16 ± 3 mg/dL/420 min [P = 0.04]; mean glycemia at 3 a.m., 225 ± 31 vs. 147 ± 17 mg/dL [P < 0.05]). The number of hypoglycemic episodes after IHE was higher than that observed after MOD (seven vs. two [P < 0.05]). Conclusions: We demonstrate that (1) CGM is a useful approach in DMT1 patients who undergo an exercise program and (2) IHE is associated with delayed nocturnal hypoglycemia.