Exercise dosage is a factor of exercise frequency, intensity and duration. Recent clinical trials show positive effects at both short term-(end of intervention) and at long term follow ups (6- and 12 months), in favor of high repetitive high dosage exercise therapy compared to a relatively lower exercise dosage in patients with long-term subacromial pain and in patients with long term patello femoral pain syndrome. Compared to treatment as usual, exercise therapy has also been shown to be effective as postsurgical rehabilitation after arthroscopic surgery in patients with knee pain with a verified ruptured mensicus. In this present clinical trial, which is a Nordic collaborative project with researchers from different research groups in Sweden and Norway, we intend to investigate short and long-term effects comparing high dosage exercise therapy versus a low repetitive low dosage exercise program in patients diagnosed with knee osteoarthritis. Primary outcome is pain (VAS) and knee function (The Knee Injury and Osteoarthritis Outcome Score (KOOS)). Since it is unknown which patients will respond to the different exercise dosages, we will also look at different prognostic factors related to patient`s beliefs regarding exercise therapy as well as different psychosocial variables as anxiety, depression, fear of movement, catastrophizing, life satisfaction and level of self-efficacy. We hope this study will increase our knowledge regarding positive and negative predictors for outcome.