It has been reported that insulin basal rate reduction initiated at exercise onset can reduce the hypoglycemic risk during exercise. However, another potentially more efficient strategy to prevent exercise-induced hypoglycemia could be to reduce insulin basal rate a certain time prior to exercise. No study investigated what would be the best timing to initiate such temporary basal insulin reduction. Therefore, the objective of this study will be to compare the efficacy of three strategies to prevent exercise-induced hypoglycemia during a 45 min exercise at 60% VO2peak (moderate intensity): 1) reduce insulin basal rate at the time of exercise; 2) reduce insulin basal rate 20 minutes prior to exercise; 3) reduce insulin basal rate 40 minutes prior to exercise. Investigators hypothesize that the time spent in hypoglycemia will be less when the insulin basal rate is reduced 40 minutes prior to exercise compared to a reduction at the time of exercise. Secondary hypotheses are: 1) Time spent in hypoglycemia will be less when the insulin basal rate is reduced 20 minutes prior to exercise compared to a reduction at the time of exercise; 2) Time spent in hypoglycemia will be less when the insulin basal rate is reduced 40 minutes prior to exercise compared to a reduction 20 minutes prior to exercise.

Inclusion Criteria:

1. Males and females ≥ 18 years of old.
2. Clinical diagnosis of type 1 diabetes for at least one year.
3. The subject will have been on insulin pump therapy for at least 3 months.
4. Last (less than 2 months) HbA1c ≤ 12%.

Exclusion Criteria:

1. Clinically significant microvascular complications: nephropathy (estimated glomerular filtration rate below 40 ml/min), neuropathy (especially diagnosed gastroparesis) or severe proliferative retinopathy as judged by the investigator.
2. Recent (< 3 months) acute macrovascular event e.g. acute coronary syndrome or cardiac surgery.
3. Abnormal blood panel and/or anemia.
4. Ongoing pregnancy.
5. Severe hypoglycemic episode within two weeks of screening.
6. Other serious medical illness likely to interfere with study participation or with the ability to complete the exercise periods by the judgment of the investigator (e.g. orthopedic limitation).
7. Failure to comply with team's recommendations (e.g. not willing to change pump parameters, etc.).