Regular sustained physical activity creates a cardiac remodelling : it is athlete's heart. In our preliminary work published in 2016, the investigators demonstrated in a small population of triathletes that there is also a vascular remodelling named athlete's artery. Moreover, the investigators know that left ventricle and aorta behave together like a couple. So they want to study by Cardiovascular Magnetic Resonance Imaging the impact of triathlon on the cardiac AND aortic remodelling.

Inclusion Criteria:

• to be enrolled in a social security plan.

• to have a BMI between 18,5 and 25 kg/m²

• to have received full information on the organization of the research and having signed its informed consent

• to have carried out a clinical screening adapted to the research

  *** Triathlete group:

• to have a minimum performance level: between 2h and 2h45 on an M triathlon during the past year (provide proof),

• to participate in 2018 in a long distance triathlon, i. e. at least distance L

• to have a defined training volume: less than 8 hours per week during the winter months and between 10 and 15 hours per week in preparation of the objective

  ***Control group:

• to have no more than 150 minutes of moderate physical activity per week (footing, brisk walking, cycling, etc.).

Exclusion Criteria:

• Persons referred to in Articles L. 1121-5 to L. 1121-8 and L1122-2 of the Public Health Code
• Cardiovascular history including Ii.e. known heart rhythm disorders
• Chronic disease: diabetes, high blood pressure...
• Long-term drug therapies that may modify cardiovascular remodeling such as Conversion Enzyme Inhibitor, Angiotensin II Receptor Antagonist,
• Active smoking, even if occasional
• Contraindication to MRI