Context: Exercise increases the risk of hypoglycemia in type 1 diabetes.

Objective: This study aimed to investigate how the amount of glucose required to prevent an exercise-mediated fall in glucose level changes over time in adolescents with type 1 diabetes.

Setting: The study took place at a tertiary pediatric referral center.

Design, Participants and Intervention: Nine adolescents with T1DM (5 males:4 females, age 16 ± 1.8 yr, diabetes duration 8.2 ± 4.1 yr, HbA1c 7.8 ± 0.8%, mean ± SD) were subjected on two different occasions to a rest or 45 min of exercise at 95% of their lactate threshold. Insulin was administered intravenously at a rate based on their usual insulin dose, with similar plasma insulin levels for both studies (82.1 ± 19.0, exercise vs. 82.7 ± 16.4 pmol/l, rest). Glucose was infused to maintain euglycemia for 18 h.

Main Outcome Measures: Glucose infusion rates required to maintain euglcycemia and levels of counterregulatory hormones were compared between rest and exercise study nights.

Results: Glucose infusion rates to maintain stable glucose levels were elevated during and shortly following exercise compared with the rest study, and again from 7-11 h following exercise. Counterregulatory hormone levels were similar between exercise and rest studies except for peaks in the immediate post-exercise period (epinephrine, norepinephrine, growth hormone and cortisol peaks: 375.6 ± 146.9 pmol/l, 5.59 ± 0.73nmol/l, 71.9 ± 14.8 mIU/l and 558 ± 69 nmol/l, respectively).

Conclusions: The biphasic increase in glucose requirements to maintain euglycemia after exercise suggests a unique pattern of early and delayed risk for nocturnal hypoglycemia following afternoon exercise.