Just 75 minutes of exercise per week helps improve fitness levels for postmenopausal women who are overweight

May 16 2007

New research indicates that even small amounts of physical activity, approximately 75 minutes a week, can help improve the fitness levels for postmenopausal women who are sedentary and overweight or obese, according to a study in the May 16 issue of JAMA.

Low levels of cardiorespiratory fitness are associated with high risk of cardiovascular disease (CVD) and death, and improvements in fitness are associated with a reduction in these risks. Physical activity habits are the primary determinant of fitness in adults and changes in physical activity result in changes in fitness, according to background information in the article. However, there is a poor understanding of the relationship between levels of physical activity and the change in fitness levels.

Timothy S. Church, M.D., M.P.H., Ph.D., of the Louisiana State University System, Baton Rouge, La., and colleagues examined the effect of 50 percent, 100 percent, and 150 percent of the NIH Consensus Panel physical activity recommendations on cardiorespiratory fitness in sedentary, overweight or obese postmenopausal women with elevated blood pressure. The Panel recommends at least 30 minutes of moderate-intensity physical activity on most, preferably all, days of the week. The study included 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.

Participants were randomly assigned to 1 of 4 groups: 102 to the nonexercise control group, 155 to the 4-kcal/kg (400 calories), 104 to the 8-kcal/kg (800 calories), and 103 to the 12-kcal/kg (1,200 calories) per week energy-expenditure groups for the 6-month intervention period. Target training intensity was the heart rate associated with 50 percent (a modest intensity) of each woman's peak VO2 (a measure of oxygen consumption and fitness level).

The average minutes of exercising per week were 72.2 for the 4-kcal/kg, 135.8 for the 8-kcal/kg, and 191.7 for the 12-kcal/kg per week exercise groups. Compared with the control group, the VO2abs (absolute) increased by 4.2 percent in the 4-kcal/kg, 6.0 percent in the 8-kcal/kg, and 8.2 percent in the 12-kcal/kg per week groups. 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.

"Perhaps the most striking finding of our study is that even activity at the 4-kcal/kg per week level [approximately 72 min/wk over about three days] was associated with a significant improvement in fitness compared with women in the nonexercise control group," the authors write. "This information can be used to support future recommendations and should be encouraging to sedentary adults who find it difficult to find the time for 150 minutes of activity per week, let alone 60 minutes per day."

Editorial: Dose-Response Relation Between Physical Activity and Fitness - Even a Little Is Good; More Is Better

In an accompanying editorial, I-Min Lee, M.B.B.S., Sc.D., of the Brigham and Women's Hospital and Harvard Medical School, Harvard School of Public Health, Boston, comments on the study concerning physical activity levels and fitness.

"Although the trial by Church et al shows a linear dose-response relation between physical activity and improvements in physical fitness, with benefit observed beginning at 72 minutes a week of moderate activity, it is limited in its ability to provide direct answers for other patterns of physical activity. Understandably, because of cost and feasibility reasons, the trial mimicked only three physical activity patterns that can occur; in real life, there are infinitely more."

"Although current knowledge regarding the dose-response relation between physical activity and health remains incomplete, the study by Church et al does provide important information on the dose of physical activity to improve physical fitness, a strong predictor of chronic disease and premature mortality. This may be succinctly summarized for patients and clinicians as "Even a little is good; more may be better!"

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