Effects of strength training on the incidence and progression of knee osteoarthritis

Objective. Quadriceps weakness is a risk factor for incident knee osteoarthritis (OA). We describe a randomized controlled trial of effects of lower-extremity strength training on incidence and progression of knee OA. Methods. A total of 221 older adults (mean age 69 years) were stratified by sex, presence of radiographic knee OA, and severity of knee pain, and were randomized to strength training (ST) or range-of-motion (ROM) exercises. Subjects exercised 3 times per week (twice at a fitness facility, once at home) for 12 weeks, followed by transition to home-based exercise after 12 months. Assessments of isokinetic lower-extremity strength and highly standardized knee radiographs were obtained at baseline and 30 months. Results. Subjects in both groups lost lower-extremity strength over 30 months; however, the rate of loss was slower with ST than with ROM. Compared with ROM, ST decreased the mean rate of joint space narrowing (JSN) in osteoarthritic knees by 26% (P = not significant). However, the difference between ST and ROM groups with respect to frequency of knee OA progression in JSN consensus ratings was marginally significant (18% versus 28%; P = 0.094). In knees that were radiographically normal at baseline, JSN > 0.50 mm was more common in ST than in ROM (34% versus 19%; P = 0.038). Incident JSN was unrelated to exercise adherence or changes in quadriceps strength or knee pain. Conclusion. The ST group retained more strength and exhibited less frequent progressive JSN over 30 months than the ROM group. The increase in incident JSN > 0.50 mm in ST is unexplained and requires confirmation.