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Exercise and Fitness: Benefits at Half Pace
By Donal P. O'Mathúna, PhD, Dr. O'Mathúna is a lecturer in Health Care Ethics, School of Nursing, Dublin City University, Ireland; he reports no consultant, stockholder, speaker's bureau, research, or other financial relationships with companies having ties to this field of study.
Source: Church TS, et al. Effects of different doses of physical activity on cardiorespiratory fitness among sedentary, overweight or obese postmenopausal women with elevated blood pressure: A randomized controlled trial. JAMA 2007;297:2081-2091.
Abstract: 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. The objective of this study was to examine the effect of 50%, 100%, and 150% of the NIH Consensus Development Panel recommended physical activity dose on fitness in postmenopausal women.
This randomized controlled trial study enrolled 464 sedentary, postmenopausal overweight or obese women whose body mass index (BMI) ranged from 25.0 kg/m2 to 43.0 kg/m2 and whose systolic blood pressure ranged from 120.0 mm Hg to 159.9 mm Hg. Enrollment took place between April 2001 and June 2005 in the Dallas, TX, area. Participants were randomly assigned to one of four groups: non-exercise control group (n = 102), 4 kcal/kg (n = 155), 8 kcal/kg (n = 104), and 12 kcal/kg (n = 103) 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.
The primary outcome was aerobic fitness assessed on a cycle ergometer and quantified as peak absolute oxygen consumption (VO2abs, L/min). The mean (SD) baseline VO2abs 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 VO2abs 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 < 0.001 for each vs. control; P for trend < 0.001). There was no treatment x subgroup interaction for age, BMI, weight, baseline VO2abs, race/ethnicity, or baseline hormone therapy use. There were no significant changes in systolic or diastolic blood pressure values from baseline to six months in any of the exercise groups vs. the control group.
In this study, previously sedentary, overweight or obese postmenopausal women experienced a graded dose-response change in fitness across levels of exercise training.
There is a clear connection between lack of fitness and higher risk of cardiovascular disease (CVD) and other causes of mortality. The National Institutes of Health (NIH) Consensus Development Panel recommendations have been adopted by many other organizations. They recommend that people should participate in at least 30 minutes of moderate-intensity physical activity on most days of the week, and preferably every day. However, little direct research has examined whether people exercising at less than or more than the NIH Consensus Panel recommendations will get varying degrees of benefit in their fitness levels. This question was addressed in this study, the Dose-Response to Exercise in postmenopausal Women (DREW) trial.
The participants in the study were postmenopausal women who were sedentary, overweight or obese, and had high blood pressure. This focus was chosen because CVD is the primary cause of death among postmenopausal women, yet one-third report no physical activity. Fitness levels generally decline by 1-2% per year among postmenopausal women. Understanding the gains of various "doses" of physical activity may help encourage the implementation of exercise recommendations.
The study's main finding, that there is a strong dose-response effect between exercise and fitness, is not surprising. Now there are data to support it. However, those who are sedentary and planning to begin an exercise regimen can be encouraged by the finding that adding half of the recommended amount of physical activity can bring significant fitness benefits. On average, those adding the smaller amount of exercise engaged in physical activity of moderate intensity for approximately 72 minutes accumulated over three days per week (which is less frequent than the recommendations). Given that sedentary people report that the most common reason they do not exercise is lack of time, the DREW study shows that even adding modest amounts of exercise can make a difference in one's fitness. Those who find the NIH Consensus Panel recommendations too time-consuming, or view them as unattainable, should be encouraged that they may reap some benefits from adding some amount of physical activity.
In spite of the positive changes in fitness, most CVD risk factors did not change significantly. Neither did people's blood pressure change significantly nor was there significant weight loss in any of the groups. Participants were informed that this was not a weight-loss trial and were asked not to make lifestyle changes. These findings are generally to be expected given the duration of the study and the relatively low intensity of the exercise. However, all exercise groups did report significant decreases in waist circumference compared to the control group. Exercise without dietary modification is known to have little impact on body weight. However, reduction in waist circumference may be clinically important in reducing the risk of diabetes.
Another interesting finding from the study relates to the way participants increased their physical activity. The study itself involved participants in structured exercise programs 3-4 days/week for six months. Participants alternated between using exercise bicycles and treadmills. Some raise concerns that when sedentary people begin structured exercise programs they reduce other physical activity because they are more tired; others claim the structured exercise invigorates people and they add even more physical activity at other times. The participants in the DREW study wore step counters at all times except when doing the structured exercise. These found no changes in any of the groups for general physical activity outside of the structured exercise.
The take-home message from this study has some good news, but also some cautions. Risk factors for CVD include lack of fitness and overweight. The good news from DREW is that exercising at only half the recommended level can bring some fitness benefits. However, this is not going to quickly change lipid profiles or blood pressure levels that correlate with cardiac health. The bad news is that weight loss did not occur with exercise alone, even when exercising at 150% of the recommended level, which averaged out at 192 minutes per week. If weight loss is the goal, exercise must be combined with dietary interventions. But if 30 minutes of exercise a day seems unattainable, start somewhere. Even a little seems to be of some benefit.