 The investigators will investigate whether high-intensity exercise training can safely improve physical performance in long-term stable heart, kidney, lung, and liver transplant recipients. Adult transplant recipients will participate in Transplantoux, a 6-month individualized home- and group-based training program, with the goal to cycle the Mont Ventoux in France. The investigators will do cardiopulmonary exercise testing : maximal oxygen consumption, maximal power and BMI. 