BACKGROUND: Prescription of resistance training (RT) exercises is an essential aspect of management for knee osteoarthritis (OA). However, whether patients with knee OA who are randomly assigned to receive RT simply substitute RT for other modes of physical activity remains unclear. OBJECTIVE: The aim of this study was to determine the effect of a structured RT intervention on overall levels of moderate- and vigorous-intensity physical activity (MVPA) in patients with early-onset knee OA. The study compared patients with early-onset OA who participated in an RT program, those who participated in a self-management (SM) program, and those who participated in both RT and SM. Because participants randomly assigned to receive the RT intervention may simply switch activity modes, resulting in little net effect, we assessed total MVPA in addition to tracking changes in strength (force-generating capacity). DESIGN AND INTERVENTION: This study was a randomized controlled trial comparing the effectiveness of SM alone, RT alone, and combined RT+SM on MVPA in patients with early OA of the knee. SETTING: The study was conducted on a university campus, with patient recruitment from the local community. PARTICIPANTS: The participants in this study were 171 patients (74% women, 26% men) with knee OA. They had a mean age of 55.1 (SD 7.1) years, a mean body mass index of 27.6 (SD 4.2) kg/m2, and radiographic status of grade II OA (and no higher) in at least one knee, as defined by the Kellgren and Lawrence classification. They wore an accelerometer while awake (mean 14.2 (SD 2.2) hours) for 5 to 7 contiguous days (mean 6.8 (SD 0.5) days) at baseline and at 3 and 9 months of intervention. RESULTS: The participants engaged in MVPA a mean of 26.2 (SD 19.3) minutes per day at baseline. Both groups significantly increased their MVPA from baseline to 3 months (RT group by 18% (effect size (d) = 0.26); SM group by 22% (effect size (d) = 0.25)), but only the RT group sustained those changes at 9 months (RT group maintained a 10% increase (effect size (d) = 0.15); SM group maintained a 2% increase (effect size (d) = 0.03)). A significant group x time interaction for MVPA indicated that the RT group maintained higher MVPA levels than the SM group. LIMITATIONS: Lack of direct measures of energy expenditure and physical function was a limitation of the study. CONCLUSIONS: Patients with early-onset OA of the knee can engage in an RT program without sacrificing their overall MVPA levels. These results support the value of RT for management of knee OA.

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