BACKGROUND: Total knee arthroplasty (TKA) alleviates pain, but muscle strength and function is reduced for a long period postoperatively. AIM: To investigate whether maximal strength training (MST) is more effective in improving muscle strength than standard rehabilitation (SR) after TKA. DESIGN: A randomized, controlled study. SETTING: Community physical therapy centers and University hospital research department. POPULATION: Forty-one adults <75 years with primary, unilateral osteoarthritis of the knee scheduled for TKA. METHODS: Participants were randomized to supervised MST of the lower extremities 3 times/week for 8 weeks and physiotherapy session1/week (N.=21) or to SR, including physiotherapy sessions/telephone contact 1/week and writing home exercise logs (N.=20). Maximal strength in leg press and knee extension, 6-minute walk test, patient-reported functional outcome score and pain were assessed preoperatively, 7 days, 10 weeks and 12 months postoperatively. RESULTS: The MST group exceeded preoperative levels of muscle strength in leg press and knee extension by 37% and 43%, respectively at 10 weeks' follow-up, and the increase was higher than in the SR group (P≤0.001). Strength differences persisted up to 12-months follow-up. At 12 months, both groups recovered to normative levels in the 6-Minute Walk Test, with no statistically significantly difference between the groups. CONCLUSIONS: Participants undergoing MST experienced superior increases in leg press and knee extension muscle strength compared with those managed with SR from 7-day to 10-week follow-up. The difference in muscle strength was maintained at 12-month follow-up. No differences in functional performance were found at any time-point. CLINICAL REHABILITATION IMPACT: Exercises after TKA should be performed with high intensity and target the operated leg specifically.