Inclusion Criteria:  Male adults (18-40 years old) with T1D, diagnosed since > 1 year Using a CGM (Dexcom G5) or willing to wear a CGM (Dexcom G5) for the duration of the study.  The CGM must be applied >48h before the exercise test  Participants are on intensified insulin therapy (MDI) or insulin pump therapy (CSII) 6% ≤ HbA1c ≤ 8% Having a self-reported moderate activity level on the iPAQ (Internationally Physical Activity Questionnaire). C-peptide <0.2 nmol/l The Physical Activity Coefficient has not changed in the 2 months prior to the first Exercise Test. 20kg/m2 < BMI < 25kg/m2  Exclusion Criteria:  Recently diagnosed T1D (< 12mo) Participants not on MDI or CSII Musculoskeletal disorder that affects cycling or is a contra-indication for vigorous physical activity Cardiorespiratory disease or ECG abnormality that is a contra-indication for vigorous physical activity Having an acute illness (e.g. influenza) that interferes with glucose metabolism Having a metabolic disorder (different from diabetes) or takes drugs known to have significant interference with glucose metabolism, such as systemic corticoids as judged by the investigator Current treatment with drugs known to have significant interference with glucose metabolism, such as systemic corticoids as judged by the investigator Presence of concomitant pathology such as heart failure, liver failure, kidney failure defined as eGFR <45mL/min Patient not able or willing to sign the patient informed consent