Knee strength maintained despite loss of lean body mass during weight loss in older obese adults with knee osteoarthritis

Background. The effects of weight loss on muscle function in older adults have not been well studied. This study determined the effects of a 6-month weight-loss intervention on muscle strength and quality in older obese adults with knee ostcoarthritis. Methods. Participants were randomized to a weight loss (WL) (n = 44,70 +/- 6 years) or weight stable (WS) (n = 43, 69 +/- 6 years) group. The WL intervention consisted of weekly educational meetings, a meal replacement diet, and a three-session-per-week structured exercise program to achieve 10%-12% weight loss. The WS intervention included bimonthly group meetings and newsletters. Body composition and knee extensor strength were measured at baseline and after intervention. Results. The WL group decreased body weight, lean body mass, fat mass, and percent body fat (p < .001 for all). Concentric extension strength increased 25% in wL (p > .05), whereas eccentric extension decreased 6% in WS (p = .028). Concentric muscle quality (strength per kg body weight or lean body mass) increased in WL (p < .05), whereas eccentric muscle quality decreased in WS (p < .05). Changes in lean body mass and fat mass were inversely associated with changes in most muscle strength and quality measures (p < .05). Men and women did not differ in response to the intervention in knee strength outcomes. Conclusions. Hypocaloric dieting in combination with exercise training had beneficial effects on muscle strength/ quality, despite loss of lean body mass in this sample of older men and women. Greater fat loss was associated with greater gains in muscle strength and quality. More studies are needed regarding the mechanisms by which loss of fat mass increases muscle strength and quality.