The purpose of this study was to examine the effects of 10 weeks of aerobic endurance training (AET), resistance exercise training (RET), or a control (CON) condition on absolute and relative fat mass (FM) or fat-free mass (FFM) in the total body (TB) and regions of interest (ROIs) of sedentary overweight middle-aged males and females. Following prescreening, 102 subjects underwent anthropometric measurements, dual-energy x-ray absorptiometry, and strength and aerobic exercise testing. Randomized subjects (male RET, n = 16; female RET, n = 19; male AET, n = 16; and female AET, n = 25) completed supervised and periodized exercise programs (AET, 30 to 50 min cycling at 70% to 75% maximal heart rate; RET, 2 to 4 sets x 8 to 10 repetitions of 5 to 7 exercises at 70% to 75% 1 repetition maximum) or a nonexercising control condition (male CON, n = 13 and female CON, n = 13). Changes in absolute and relative TB-FM and TB-FFM and ROI-FM and ROI-FFM were determined. At baseline, and although matched for age and body mass index, males had greater strength, aerobic fitness, body mass, absolute and relative TB-FFM and ROI-FFM, but reduced absolute and relative TB-FM and ROI-FM, compared with females (p < 0.05). After training, both female exercise groups showed equivalent or greater relative improvements in strength and aerobic fitness than did the male exercise groups (p < 0.05); however, the male exercise groups increased TB-FFM and reduced TB-FM more than did the female exercise groups (p < 0.05). Male AET altered absolute FM more than male RET altered absolute FFM, thus resulting in a greater enhancement of relative FFM. Despite equivalent or greater responses to RET or AET by female subjects, the corresponding respective increases in FFM or reductions in FM were lower than those in males, indicating that a biased dose-response relationship exists between sexes following 10 weeks of exercise training.

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