Collection of venous blood samples in male T1D patients to evaluate the behavior of different biomarkers (beta-hydroxybutyrate, lactate, glucose) during and after morning Aerobic (60% of VO2 max) and Symptom Limited Maximal Exercise Test.

Compare values and trends of different biomarkers (glucose, lactate and beta-hydroxybutyrate) before, during and after morning aerobic and symptom limited maximal exercise (cycling) to predict glycemic fluctuations (hypo- and hyperglycemic events) during and after exercise in order to create treatment algorithms to prevent these events.

Endpoint:

• Evaluate values and trends of glucose, lactate and beta-hydroxybutyrate before, during and after morning exercise in venous blood.

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

Adult male participants, aged 18-40 years, with Type 1 Diabetes (T1D) treated with Multiple Daily Insulin injections (MDI) and Continuous Subcutaneous Insulin Injections (CSII)