PURPOSE: This study was designed to investigate whether, in a dose-response manner, there would be greater health benefits in a group of postmenopausal women completing 45 minute- versus 30 minutes of moderate intensity (50% maximal oxygen uptake reserve, VO2R) exercise 5 days/wk. METHODS: Apparently healthy but sedentary postmenopausal women (n = 33) were randomized to a nonexercise control group, a 30-minute exercise duration group, or a 45-minute exercise duration group. Exercise training was performed 5 days/wk for 12 weeks at 50% VO2R. Participants were instructed to not change their usual diet throughout the study. RESULTS: Twenty-six women completed the study. After 12 weeks, VO2max increased significantly (p < 0.05) in both 30-minute (0.20 +/- 0.21 L/min) and 45-minute (0.41 +/- 0.10 L/min) groups. Repeated measures ANOVA identified a significant interaction between exercise duration and VO2max values (F = 4.72, p < 0.05), indicating that VO2max responded differently to 30-minute and 45-minute exercise durations. Trend analysis showed that body mass, body composition, waist circumference, and high-density lipoprotein cholesterol (HDL-C) changed favorably (p < 0.05) across control, 30-minute, and 45-minute groups. CONCLUSIONS: Although most health organizations agree that 150 min/wk of physical activity will reduce the risk of all-cause and cardiovascular mortality, few randomized, controlled studies have examined whether completing more physical activity than the recommended amount will yield additional benefits. Findings from the present study suggest that there is a dose-response relationship between exercise duration and numerous health outcomes in postmenopausal women, including cardiorespiratory fitness, body mass, body composition, waist circumference, and HDL-C.

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