Inclusion Criteria:  Males and females aged 14-23 years old  Athletes competing in endurance sports at national or international level for at least 2 years. Sports include:  Triathlon Cycling Distance running (≥ 1500 meters) Rowing Swimming Non athletes engaged in < 3 hours per week of physical activity  Exclusion Criteria:  Medical history of cardiovascular disease Current smoker of past history of smoking Diabetes mellitus