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A Randomized Controlled Trial

Timothy S. Church, MD, MPH, PhD; Conrad P. Earnest, PhD; James S. Skinner, PhD; Steven N. Blair, PED

JAMA. 2007;297:2081-2091.

Context  Low levels of cardiorespiratory fitness are associated with high risk of mortality, and improvements in fitness are associated with reduced mortality risk. However, a poor understanding of the physical activity–fitness dose response relation remains.

Objective  To examine the effect of 50%, 100%, and 150% of the NIH Consensus Development Panel recommended physical activity dose on fitness in women.

Design, Setting, and Participants  Randomized controlled trial of 464 sedentary, postmenopausal overweight or obese women whose body mass index ranged from 25.0 to 43.0 and whose systolic blood pressure ranged from 120.0 to 159.9 mm Hg. Enrollment took place between April 2001 and June 2005 in the Dallas, Tex, area.

Intervention  Participants were randomly assigned to 1 of 4 groups: 102 to the nonexercise control group and 155 to the 4-kcal/kg, 104 to the 8-kcal/kg, and 103 to the 12-kcal/kg per week energy-expenditure groups for the 6-month intervention period. Target training intensity was the heart rate associated with 50% of each woman's peak O₂.

Main Outcome Measure  The primary outcome was aerobic fitness assessed on a cycle ergometer and quantified as peak absolute oxygen consumption (O₂abs, L/min).

Results  The mean (SD) baseline O₂abs values were 1.30 (0.25) L/min. The mean (SD) minutes of exercising per week were 72.2 (12.3) for the 4-kcal/kg, 135.8 (19.5) for the 8-kcal/kg, and 191.7 (33.7) for the 12-kcal/kg per week exercise groups. After adjustment for age, race/ethnicity, weight, and peak heart rate, the exercise groups increased their O₂abs compared with the control group by 4.2% in the 4-kcal/kg, 6.0% in the 8-kcal/kg, and 8.2% in the 12-kcal/kg per week groups (P<.001 for each vs control; P for trend <.001). There was no treatment x subgroup interaction for age, body mass index, weight, baseline O₂abs, race/ethnicity, or baseline hormone therapy use. There were no significant changes in systolic or diastolic blood pressure values from baseline to 6 months in any of the exercise groups vs the control group.

Conclusion  In this study, previously sedentary, overweight or obese postmenopausal women experienced a graded dose-response change in fitness across levels of exercise training.

Trial Registration  clinicaltrials.gov Identifier: NCT00011193

Author Affiliations: Pennington Biomedical Research Center, Louisiana State University System, Baton Rouge (Drs Church and Earnest); Department of Kinesiology, Indiana University, Bloomington (Dr Skinner); and Arnold School of Public Health, University of South Carolina, Columbia (Dr Blair).

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