A Bit of Exercise Improves Fitness For Sedentary Heavy Women

BATON ROUGE, La., May 16 -- For postmenopausal women who are sedentary, overweight, or obese, peddling an exercise bike for just a few minutes a week can improve cardiorespiratory fitness, found researchers here.

But although riding the bike for 75 minutes a week, spread over three days, improved cardiorespiratory fitness, most other cardiovascular risk factors held firm, said Timothy S. Church, M.D., Ph.D., of Louisiana State University here, and colleagues.

These included blood pressure, lipid profiles, and weight, Dr. Church and colleagues reported in the May 16 issue of the Journal of the American Medical Association.

Nevertheless, low fitness is a powerful, independent risk factor for premature mortality, and it is important to understand the effects of different doses of physical activity, particularly for women with cardiovascular disease, type 2 diabetes, and other chronic diseases, the investigators said.

To examine the effect of 50%, 100%, and 150% physical activity dose on women's fitness, as recommended by a 1996 NIH consensus panel, the researchers undertook the randomized controlled DREW trial (Dose Response to Exercise in postmenopausal Women).

The independent advisers who comprised the NIH panel has recommended at least 30 minutes of moderate-intensity physical activity on most, preferably all, days of the week.

The DREW trial included 464 sedentary, postmenopausal overweight or obese women. Their body mass index ranged from 25.0 to 43.0 while their systolic blood pressure ranged from 120.0 to 159.9 mm Hg. Enrollment took place from April 2001 to June 2005 in the Dallas area.

In the six-month study, participants were randomized to one of four groups: 102 to the nonexercise control group; 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 six-month intervention period, target training intensity was the heart rate associated with 50% of each woman's peak VO₂.

Aerobic fitness was assessed on a cycle ergometer and quantified as peak absolute oxygen consumption (VO₂abs, L/min). Mean age of the participants was 57.3 years; about 35% were nonwhite.

The mean 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.

After adjustment for age, race/ethnicity, weight, and peak heart rate, the exercise groups increased their fitness 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, the researchers reported (P

In discussing the findings the researchers wrote that the most striking finding is that even activity at the 4-kcal/kg per week level (approximately 72 minutes a week) was associated with a significant improvement in fitness compared with women in the control group.

The group exercising at 150% of the NIH panel's recommendation (12-kcal/kg per week) had a proportionally greater increase in fitness compared with those in the 8-kcal/kg per week, the researchers said. These improvements occurred at a modest training intensity (heart rate at a 50% of peak VO₂).

The data in this study showing a that even 72 minutes of moderate physical activity per week accumulated over about three days has a significant effect on fitness in this group of sedentary women, the researchers said.

They added that they do not recommend that the public health recommendation for physical activity be lowered to less than 150 minutes a week. Nevertheless, these results should be considered, along with other new evidence on exercise dose, when revised public recommendations are developed.

The study had certain limitations, they said, primarily because the sample was limited to a specific set of women. Thus, there was no way of knowing whether the results would apply to other women or men.

To our knowledge, Dr. Church concluded, this study is the largest single-center, controlled efficacy trial of a graded dose-response change in fitness in women across different levels of exercise training.

In an accompanying editorial, I-Min Lee, MBBS, Sc.D., of the Harvard School of Public Health, wrote that it is plausible that there is a minimum dose of physical activity for health benefits and that these benefits increase with increasing dose, and that beyond a certain dose, adverse effects, such as injuries, outweigh the benefits.

In their study, Dr. Lee said, Dr. Church and colleagues provided some clarification for dose-response questions related to physical activity.

However, he said, with obesity a major health problem worldwide, sedentary, overweight or obese individuals should not be lulled into believing that 72 minutes a week of physical activity will ameliorate their weight concerns. Even at 192 minutes a week, the highest dose, trial participants did not change their diet and did not lose weight.

Therefore given the typical U.S. diet, guidelines suggesting 60 minutes or more of daily physical activity are more appropriate if weight control is the primary goal.

Dr. Lee also suggested the need for studies of other patterns of physical activity, such as running, to determine whether such activity might improve cardiovascular risk factors.

However, he said, the study by Dr. Church and his colleagues, provides important information on the dose of physical activity needed to improve physical fitness, a strong predictor of chronic disease and premature mortality.

This, Dr. Lee said, may be succinctly summarized for patients and clinicians as "Even a little is good; more may be better."

Dr. Lee reported having received investigator-initiated research funding and support as Principal Investigator from the National Institutes of Health (the National Heart, Lung, and Blood Institute and the National Cancer Institute) and research support as co-investigator from Dow Corning Corp. He also reported having received honoraria for serving as a member of the Scientific Advisory Board of the Cooper Institute and as a consultant to Virgin Life Care Inc.