Moderate exercise attenuates the loss of skeletal muscle mass that occurs with intentional caloric restriction--induced weight loss in older, overweight to obese adults

Background. Aging is associated with a loss of muscle mass and increased body fat. The effects of diet-induced weight loss on muscle mass in older adults are not clear. Purpose. This study examined the effects of diet-induced weight loss, alone and in combination with moderate aerobic exercise, on skeletal muscle mass in older adults. Methods. Twenty-nine overweight to obese (body mass index = 31.8 [+ or -] 3.3 kg/[m.sup.2]) older (67.2 [+ or -] 4.2 years) men (n = 13) and women (n = 16) completed a 4-month intervention consisting of diet-induced weight loss alone (WL; n = 11) or with exercise (WL/EX; n = 18). The WL intervention consisted of a low-fat, 500-1,000 kcal/d caloric restriction. The WL/EX intervention included the WL intervention with the addition of aerobic exercise, moderate-intensity walking, three to five rimes per week for 35-45 minutes per session. Whole-body dual-energy x-ray absorptiometry, thigh computed tomography (CT). and percutaneous muscle biopsy were performed to assess changes in skeletal muscle mass at the whole-body, regional, and cellular level, respectively. Results. Mixed analysis of variance demonstrated that both groups had similar decreases in bodyweight (WL, -9.2% [+ or -] 1.0%; WL/EX, -9.1% [+ or -] 1.0%) and whole-body fat mass (WL, -16.5%, WL/EX, -20.7%). However, whole-body fat-free mass decreased significantly (p < .05) in WL (-4.3% [+ or -] 1.2%) but not in WL/EX (-1.1% [+ or -] 1.0%). Thigh muscle cross-sectional area by CT decreased in both groups (WL, -5.2% [+ or -] 1.1%: WL/EX, -3.0% [+ or -] 1.0%) and was not statistically different between groups. Type l muscle fiber area decreased in WL (-19.2% [+ or -] 7.9%, p = .01) but remained unchanged in WL/EX (3.4% [+ or -] 7.5%). Similar patterns were observed in type II fibers (WL, -16.6% [+ or -] 4.0%; WL/EX, -0.2% [+ or -] 6.5%). Conclusion. Diet-induced weight loss significantly decreased muscle mass in older adults. However, the addition of moderate aerobic exercise to intentional weight loss attenuated the loss of muscle mass. Key Words: Weight loss--Aerobic exercise Obese--Muscle.