 The investigators have recently reported that early-commenced physical rehabilitation, including progressive strength training of the knee extensors of the operated leg seems feasible after TKA. The classic exercise-physiology literature emphasizes loading and repetitions performed to contraction failure - among others - as important variables for muscle hypertrophy and strength gains. It is currently not known how loading and repetitions performed to contraction failure during knee extensions with the operated leg, influences post-operative knee joint pain in patients with TKA. 