Total knee arthroplasty (TKA) alleviates pain, but muscle strength and function is reduced for a long period postoperatively. To investigate whether maximal strength training (MST) is more effective in improving muscle strength than standard rehabilitation (SR) after TKA. A randomized, controlled study. Community physical therapy centers and University hospital research department. Forty-one adults <75 years with primary, unilateral osteoarthritis of the knee scheduled for TKA. 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. 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. 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. Exercises after TKA should be performed with high intensity and target the operated leg specifically.