This multicentre two-phased RCT aims to evaluate implementation potential, cost-effectiveness, effectiveness, and the role of exercise intensity of a home-based exercise and physical activity intervention to improve de novo kidney transplant recipients' physical fitness, cardiovascular health, gut microbiome characteristics, and health-related quality of life. The first phase of this study comprehends a six-month exercise training intervention. Patients will be randomized into (i) a sham intervention consisting of low-intensity balance and stretching exercises (LIT), (ii) a moderate-intensity aerobic and strength training intervention (MIT), or (iii) a moderate- and high-intensity aerobic and strength training intervention (MHIT). The second phase of this study comprehends a physical activity maintenance intervention provided to MIT and MHIT but not LIT. A total of 147 de novo kidney transplant recipients will be recruited from two independent Belgian transplant centres i.e. UZ Leuven and UZ Ghent.