Changes in lower extremity muscle mass and muscle strength after weight loss in obese patients with knee osteoarthritis: A prospective cohort study

Objective To investigate the effects of low-energy dietinduced weight loss on lower-extremity muscle mass and knee muscle strength in obese patients with knee osteoarthritis (OA), and the associations of these effects. Methods. We studied 159 obese patients with knee OA and available data from body composition analysis that had been performed using dual x-ray absorptiometry scanning and isometric muscle strength testing of the knee in extension and in flexion. The data had been obtained as part of a randomized controlled trial, with measurements performed before and after a supervised low-energy diet-induced weight loss intervention lasting 16 weeks. Results. The patients lost an average of 12.9 kg (95% confidence interval [ 95% CI] 10.2, 15.7) (13% of baseline weight). The weight loss consisted of 10.9 kg fat mass (95% CI 8.9, 12.9), of which 3.8 kg (95% CI 2.7, 4.9) was leg fat mass. Total lean body mass was reduced by 1.9 kg (95% CI 0.05, 3.8), of which 0.785 kg (95% CI 0.09, 1.476) was leg lean mass. Absolute muscle strength decreased by similar to 3-4% after the weight loss, whereas body mass-normalized muscle strength increased by 11-12%. At baseline, leg lean mass was significantly related to muscle strength, but changes in these measurements at followup were not related. Conclusion. Weight loss induced by a low-energy diet led to independent losses of leg muscle tissue and strength. The weight loss was accompanied by increased normalized muscle strength along with improved self-reported disability and pain-all of which are beneficial to patients with knee OA. The present results suggest that significant weight loss in patients with knee OA should be followed by an exercise regimen to restore or increase muscle mass.