Basal Insulin Reduction 90 Minutes Before Exercise Beneficial for Glucose Control, Hypoglycemia Risk in T1D 

A 50% to 80% basal rate reduction performed 90 minutes before beginning exercise will improve open-loop glucose control and decrease the risk for hypoglycemia during exercise in individuals with type 1 diabetes.

Source: Basal Insulin Reduction 90 Minutes Before Exercise Beneficial for Glucose Control, Hypoglycemia Risk in T1D – Endocrinology Advisor