Insulin therapy and exercise

Abstract

Proper insulin management during exercise is crucial for individuals with type 1 diabetes (T1D). The goals are to enable better performance during the activity and to prevent both hypoglycemia and hyperglycemia during and after the activity. Management strategies depend on the therapy used, as well as the intensity and duration of the exercise.

• Pre-exercise considerations: When engaging in planned activities, it is vital to consider "Insulin on Board" (IOB)—referring to the circulating insulin resulting from basal doses plus any boluses administered in the hours leading up to the exercise. For those using multiple daily injection (MDI) therapy or open-loop insulin pumps, if exercising 1 to 2 hours after a meal, it is suggested that the pre-meal bolus be reduced by 25% to 75%, depending on the exercise intensity and duration. With automated insulin delivery (AID) systems, the recommendation is to set a higher glucose target 1 to 2 hours in advance for aerobic exercise, while also reducing the pre-meal bolus.
• Considerations based on activity type: Continuous aerobic exercise of mild to moderate intensity causes a drop in glucose levels, thus requiring the most significant reductions in insulin. In contrast, strength training or high-intensity interval training (HIIT) triggers hormonal responses that can stabilize—and often raise—blood glucose levels. For these predominantly anaerobic activities, reducing insulin is not recommended; in fact, a small increase in the rapid-acting insulin dose may even be necessary.
• Post-exercise recovery and monitoring: Continuous glucose monitoring (CGM) is now an indispensable tool for decision-making. Decisions regarding carbohydrate intake and insulin dosage management should be proactive—made before, during, and after exercise. It is well established that exercise increases insulin sensitivity in the hours following the activity, thereby raising the risk of hypoglycemia. It is recommended that any correction bolus administered post-exercise for reactive hyperglycemia be reduced to 50% of the dose to prevent hypoglycemia.