OBJECTIVE: To examine the long-term effects of exercise modality during weight loss on body composition and associations between body composition and physical function changes. METHODS: Two hundred forty-nine older adults (66.9 +/- 4.7 years, 71% women, 32% African American, BMI 34.4 +/- 3.7 kg/m2) were randomized to weight loss (WL; n = 82), WL plus aerobic training (WL+AT; n = 86), or WL plus resistance training (WL+RT; n = 81) for 18 months. Dual-energy x-ray absorptiometry-acquired body composition, 400-m walk time, and knee extensor strength were measured at baseline and at 6 and 18 months. RESULTS: Total body mass loss was enhanced when WL was combined with exercise (WL -5.7 +/- 0.7 kg, WL+AT -8.5 +/- 0.7 kg, WL+RT -8.7 +/- 0.7 kg; p < 0.01). Total body fat mass loss was significantly greater in WL+AT (-6.8 +/- 0.6 kg, -16.4%) and WL+RT (-7.8 +/- 0.5 kg, -19.0%) than WL (-4.8 +/- 0.6 kg, -10.9%); both p < 0.01. Lean mass loss was greatest in WL+AT (-1.6 +/- 0.3 kg, -3.1%) compared with WL+RT (-0.8 +/- 0.3 kg, -1.5%) or WL (-1.0 +/- 0.3 kg; -2.0%); both p <= 0.02. Change in 400-m walk time was associated with change in fat mass (beta/SD +6.1 s; p < 0.01), while change in knee extensor strength was associated with change in lean mass (beta/SD +1.6Nm; p < 0.01). CONCLUSIONS: WL+RT results in less lean mass lost than WL+AT; WL plus exercise yields greater fat mass loss than WL alone.

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