Real-world physical activity produces highly variable glycemic responses in individuals with T1DM. This study evaluated 8,171 activity sessions across 45 activity types from the Type 1 Diabetes Exercise Initiative to characterize hypoglycemia risk during daily physical activity.

Hypoglycemia risk was assessed using change in continuous glucose monitoring (ΔCGM), the low blood glucose index (LBGI), and hypoglycemia event occurrence. Analyses applied analysis of variance and Tukey range testing to investigate associations with activity duration, starting glucose, IoB, carbohydrate intake, and sex. Activity categories included aerobic, mixed, and anaerobic modalities.

Longer activity duration produced larger glucose declines. Median ΔCGM was −24 mg/dL for 60–120 minutes compared with −12 mg/dL for 15–30 minutes. Lower starting glucose also increased risk, and 90% of sessions that began below 50 mg/dL resulted in hypoglycemia. Higher IoB and carbohydrate intake 2-4 hours before activity were linked with greater glucose reductions, a relationship explained by lower starting glucose and higher insulin exposure. Males experienced larger glucose declines than females. Aerobic activities caused the greatest reductions compared with mixed and anaerobic activity types. Closed-loop users demonstrated lower LBGI values than open-loop users.

These findings highlight the substantial variability in glycemic responses during daily physical activity and emphasize the need for individualized approaches to prevent hypoglycemia in T1DM.