BACKGROUND: Supervised lifestyle interventions have the potential to significantly improve physical activity and fitness in patients with CKD. METHODS: To assess the efficacy of a lifestyle intervention in patients with CKD to improve cardiorespiratory fitness and exercise capacity over 36 months, we conducted a randomized clinical trial, enrolling 160 patients with stage 3-4 CKD, with 81 randomized to usual care and 79 to a 3-year lifestyle intervention. The lifestyle intervention comprised care from a multidisciplinary team, including a nephrologist, nurse practitioner, exercise physiologist, dietitian, diabetes educator, psychologist, and social worker. The exercise training component consisted of an 8-week individualized and supervised gym-based exercise intervention followed by 34 months of a predominantly home-based program. Self-reported physical activity (metabolic equivalent of tasks [METs] minutes per week), cardiorespiratory fitness (peak O2 consumption [VO2peak]), exercise capacity (maximum METs and 6-minute walk distance) and neuromuscular fitness (grip strength and get-up-and-go test time) were evaluated at 12, 24, and 36 months. RESULTS: The intervention increased the percentage of patients meeting physical activity guideline targets of 500 MET min/wk from 29% at baseline to 63% at 3 years. At 12 months, both VO2peak and METs increased significantly in the lifestyle intervention group by 9.7% and 30%, respectively, without change in the usual care group. Thereafter, VO2peak declined to near baseline levels, whereas METs remained elevated in the lifestyle intervention group at 24 and 36 months. After 3 years, the intervention had increased the 6-minute walk distance and blunted declines in the get-up-and-go test time. CONCLUSIONS: A 3-year lifestyle intervention doubled the percentage of CKD patients meeting physical activity guidelines, improved exercise capacity, and ameliorated losses in neuromuscular and cardiorespiratory fitness.