Abstract: In total, we extracted data from 54 studies. Overall, 19 (20%) studies reported adequate random sequence generation and allocation concealment and adequately accounted for incomplete outcome data; we considered these studies to have an overall low risk of bias. Studies were largely free from selection bias, but research results may be vulnerable to performance and detection bias, as only four of the RCTs reported blinding of participants to treatment allocation, and, although most RCTs reported blinded outcome assessment, pain, physical function and quality of life were participant self-reported. High-quality evidence from 44 trials (3537 participants) indicates that exercise reduced pain (standardised mean difference (SMD) -0.49, 95% confidence interval (CI) -0.39 to -0.59) immediately after treatment. Pain was estimated at 44 points on a 0 to 100-point scale (0 indicated no pain) in the control group; exercise reduced pain by an equivalent of 12 points (95% CI 10 to 15 points). Moderate-quality evidence from 44 trials (3913 participants) showed that exercise improved physical function (SMD -0.52, 95% CI -0.39 to -0.64) immediately after treatment. Physical function was estimated at 38 points on a 0 to 100-point scale (0 indicated no loss of physical function) in the control group; exercise improved physical function by an equivalent of 10 points (95% CI 8 to 13 points). High-quality evidence from 13 studies (1073 participants) revealed that exercise improved quality of life (SMD 0.28, 95% CI 0.15 to 0.40) immediately after treatment. Quality of life was estimated at 43 points on a 0 to 100-point scale (100 indicated best quality of life) in the control group; exercise improved quality of life by an equivalent of 4 points (95% CI 2 to 5 points). High-quality evidence from 45 studies (4607 participants) showed a comparable likelihood of withdrawal from exercise allocation (event rate 14%) compared with the control group (event rate 15%), and this difference was not significant: odds ratio (OR) 0.93 (95% CI 0.75 to 1.15). Eight studies reported adverse events, all of which were related to increased knee or low back pain attributed to the exercise intervention provided. No study reported a serious adverse event. In addition, 12 included studies provided two to six-month post-treatment sustainability data on 1468 participants for knee pain and on 1279 (10 studies) participants for physical function. These studies indicated sustainability of treatment effect for pain (SMD -0.24, 95% CI -0.35 to -0.14), with an equivalent reduction of 6 (3 to 9) points on 0 to 100-point scale, and of physical function (SMD -0.15 95% CI -0.26 to -0.04), with an equivalent improvement of 3 (1 to 5) points on 0 to 100-point scale. Marked variability was noted across included studies among participants recruited, symptom duration, exercise interventions assessed and important aspects of study methodology. Individually delivered programmes tended to result in greater reductions in pain and improvements in physical function, compared to class-based exercise programmes or home-based programmes; however between-study heterogeneity was marked within the individually provided treatment delivery subgroup. High-quality evidence indicates that land-based therapeutic exercise provides short-term benefit that is sustained for at least two to six months after cessation of formal treatment in terms of reduced knee pain, and moderate-quality evidence shows improvement in physical function among people with knee OA. The magnitude of the treatment effect would be considered moderate (immediate) to small (two to six months) but comparable with estimates reported for non-steroidal anti-inflammatory drugs. Confidence intervals around demonstrated pooled results for pain reduction and improvement in physical function do not exclude a minimal clinically important treatment effect. Since the participants in most trials were aware of their treatment, this may have contributed to their improvement. Despite the lack of blinding we did not downgrade the quality of evidence for risk of performance or detection bias. This reflects our belief that further research in this area is unlikely to change the findings of our review.

Plain-language summary: This summary of an update of a Cochrane review presents what we know from research about the effects of exercise for people with OA of the knee. After searching for all relevant studies up to May 2013, we added 23 new studies since the last version of the review, now including 54 studies (3913 participants), most on mild to moderate symptomatic knee OA. Except for five studies in which participants enrolled in a Tai Chi-based programme, most participants underwent land-based exercise programmes consisting of traditional muscle strengthening, functional training and aerobic fitness programmes, which were individually supervised or were provided during a class; these individuals were compared with people who did not exercise. Evidence from 44 studies (3537 participants) shows the effects of exercise immediately after treatment; 12 studies provided data on two to six-month post-treatment sustainability. Here we report only results for the immediate treatment period. Pain on a scale of 0 to 100 points (lower scores mean reduced pain). • People who completed an exercise programme rated their pain at 12 (10 to 15) points lower at end of treatment (12% absolute improvement) compared with people who did not exercise. • People who completed an exercise programme rated their pain at 32 points. • People who did not exercise rated their pain at 44 points. Physical function on a scale of 0 to 100 points (lower score means better physical function). • People who completed an exercise programme rated their physical function at 10 points (8 to 13 points) lower at end of treatment (10% absolute improvement) compared with people who did not exercise. • People who completed an exercise programme rated their physical function at 28 points. • People who did not exercise rated their physical function at 38 points. Quality of life on a scale of 0 to 100 points (higher score means better quality of life). • Overall, people who completed an exercise programme rated their quality of life at 4 points (2 to 5 points) higher at the end of treatment (4% absolute improvement). • People who completed an exercise programme rated their quality of life at 47 points. • People who did not exercise rated their quality of life at 43 points. Withdrawals. • One fewer persons out of 100 dropped out of the exercise programme (1% absolute decrease). • Out of 100 people in exercise programmes, 14 dropped out. • Out of 100 people who did not exercise, 15 dropped out. High-quality evidence shows that among people with knee OA, exercise moderately reduced pain immediately after cessation of treatment and improved quality of life only slightly, without an increase in dropouts. Further research is unlikely to change the estimate of these results. Moderate-quality evidence indicates that exercise moderately improved physical function immediately after cessation of treatment. Further research may change the estimate of these results. Most clinical studies have provided no precise information on side effects such as injuries or falls sustained during exercise, but we would expect these to be rare. Eight studies reported increased knee or low back pain attributed to the exercise programme, and all identified studies reported no injuries.