The effects of exercise on lean body mass (LBM), fat mass (FM), maximal oxygen uptake (VO2max), and quadriceps (QD) strength were studied in 72 male, mildly obese (mean 38% fat) subjects (mean age 43.5 yr) randomly assigned to one of eight treatments arranged in a 2x4 factorial plan with exercise (EX) and non-exercise (NE) and four diets as the two factors. Exercise consisted of a 3 d/wk, 8-wk aerobics program (70 to 85% maximum heart rate) accompanied by a calisthenics program. LBM was determined by whole body potassium (40K), FM by subtracting LBM from total body weight, VO2max using the Wilmore-Costill method, and QD strength with the Cybex II system. Weight loss of the combined EX (11.8 +/- 0.6 kg) (mean +/- SE) and NE (9.2 +/- 0.3 kg) groups was not statistically different. LBM of the EX group was unchanged (from 63.1 +/- 1.9 to 62.5 +/- 2.1 kg), whereas in the NE group it was reduced from 62.6 +/- 1.1 to 59.3 +/- 1.2 kg (p < 0.001) accounting for 36% of total weight loss. FM loss was greater for the EX group (11.2 +/- 1.5 kg) when compared to the NE (5.2 +/- 1.6 kg) group (p < 0.001). The EX group exhibited an increase in VO2max from 2.9 +/- 0.3 to 3.4 +/- 0.2 1 L/min (p < 0.001), whereas the NE group was unchanged (3.0 +/- 0.3 to 2.9 +/- 0.4 1 L/min (NS). QD strength increased in the EX group from 1.72 +/- 7.0 to 2.10 +/- 6.6 Nm (p < 0.001) whereas no change was found in the NE group values (NS). We conclude that the addition of EX to a caloric-deficient dietary regimen results in (1) preservation of existing LBM; (2) increase in VO2max (3) increase in strength; (4) increase in fat utilization for energy production; and (5) more effective reduction in fat stores than diet alone.

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