That physical activity is good for us is hardly a new idea. The ancient Greeks and Chinese, for example, prescribed physical activity for a healthier and longer life. Nowadays, we have hundreds of medical studies to confirm that it works. Physical activity can lower our risk for a wide variety of conditions, including heart disease, colon cancer, obesity, hypertension, diabetes, osteoporosis, and depression. It also improves immune, joint, cardiac, and brain function. Yet 30% of American women are completely sedentary in their leisure time. Another 50% do something, but not – according to public health researchers – at a level that would yield optimal health benefits.
Part of the problem is a lack of specifics. We know that exercise can improve our health, but we’re not always sure what level or kind of exercise would be best. As a result, we may not settle on any form of regular exercise.
In addition, official recommendations may have discouraged sedentary women from even starting. In the 1970s and 1980s, “no pain, no gain” was a popular catch phrase. Official recommendations shared that outlook. Sustained, vigorous exercise – such as running or aerobics, three to five days a week – was considered necessary to raise the heart rate and oxygen intake to levels sufficient for cardiac fitness.
By the mid-1990s, recommendations had become less demanding, partly to encourage more people to exercise. Updated federal guidelines advised all adults to accumulate at least 30 minutes of moderate-intensity physical activity (brisk walking is the typical example) on most days of the week. Both old and new recommendations would expend approximately 1,000 calories per week, but many people, including researchers, still wonder whether moderate activities offer the same health benefits as vigorous activities.
How to Burn an Extra 150 Calories
We measure energy expenditure through physical activity in calories. Light activities – such as casual walking, bowling, and yoga – do not burn calories as quickly as vigorous exercise like jogging and singles tennis, so they require more time to burn an equivalent number of calories. Current federal health guidelines for physical activity call for at least 30 minutes of brisk walking on most days of the week. A 30-minute walk at a 3-4 mph pace expends about 150 calories. Here are some other ways for a 150-pound woman to accomplish the same thing.
Activity – Approximate Time (in minutes)
Bicycling (6 mph) 38
Golfing (carrying bag and walking) 26
Hiking (40-pound pack) 22
Jogging (5.5 mph) 12
Running (7.5 mph) 11
Raking leaves 35
Skating (ice or roller) 30
Swimming (slow crawl) 17
Tennis (singles) 23
Walking (3 – 4 mph) 30
Weight training 20
Exercise times are calculated for a 150-pound person. If you weigh less than 150 pounds, you’ll burn fewer calories per minute and will have to work out longer to expend 150 calories. If you weigh more than 150 pounds, you’ll burn 150 calories in a shorter time.
Physical Activity and Women
Much of the data has come from epidemiological studies showing an inverse association between physical activity and coronary heart disease (CHD). Although this subject has been less thoroughly studied in women than in men, an increasing body of evidence over the past decade indicates that active women have lower CHD rates than inactive women. We also know that physical activity helps us live longer: the more physically fit we are, the lower our risk of dying, not just from CHD, but from all causes. This is as true for women as it is for men.
Recent research has focused on the kinds and intensity of physical activities that are associated with lower risk. The Nurses’ Health Study, for example, found that women who walk briskly three hours a week are as well-protected from heart disease as women who spend one and a half hours a week in more vigorous activities, such as aerobics or running. Women in the study who engaged in either form of exercise had a rate of heart attacks 30%-40% lower than that of sedentary women.
Now a new study suggests that walking even one hour per week can lower risk for CHD among relatively sedentary women. This should be encouraging news to those women who have been unenthusiastic about – or unable to begin or stick with – a more vigorous exercise program.
An Intriguing Study
Harvard Medical School researchers with the Women’s Health Study reported in the March 21, 2001, Journal of the American Medical Association (JAMA) on the association between CHD and physical activity in nearly 40,000 healthy women, ages 45 and over. The Women’s Health Study is a randomized, controlled trial of aspirin and vitamin E for primary prevention of cardiovascular disease and cancer.
At the start of the trial, participants were asked to estimate how much time they spent each week on activities such as walking, jogging, running, bicycling, aerobic exercise, tennis, and lap swimming. They also reported their usual pace of walking and the number of flights of stairs they climbed each day. Researchers calculated calorie expenditure for all of these activities. They also took into account other factors that influence CHD risk, such as weight, smoking status, diet, medical history, and use of postmenopausal hormones. The women were followed for five years, while the researchers tracked coronary events and deaths from CHD.
As expected, the more that women exercised, the lower their risk for heart disease. Those who expended at least 1,000 calories per week – the amount recommended by both the old and new guidelines – experienced a significant reduction in CHD risk compared with the least active women. Vigorous activity in particular reduced the risk by 37%. The researchers analyzed walking separately in the 58% who didn’t engage in vigorous exercise. They found that women who walked at least an hour a week had a CHD risk about half that of women who didn’t walk. Moreover, at this level of exercise, pace was not an important factor.
In a separate analysis, the researchers found that the benefits of physical activity are not confined to women at especially low risk. The inverse association of physical activity and CHD risk was also found in women who smoked, were overweight, or had elevated cholesterol.
Some Implications for Sedentary Women
It might seem surprising that as little as one hour a week of even casual walking could lower CHD risk. Part of the explanation lies with the study population. Women in this study were fairly inactive. We know from other research that the greatest observable cardiovascular gains are made when a sedentary person becomes moderately active. Among people who are already active, more vigorous exercise is needed to see additional benefits.
How to Get – and Keep – Going
Most of us are short on time. But physical activity is so valuable to our health that it pays to figure out how to fit more of it into our lives. Even if you can’t manage the recommended 30 minutes of moderate physical activity on most days, don’t give up. Try exercising for shorter amounts of time, spread throughout the day. Here are some other strategies:
- Set aside a certain time every day for exercise – even if it’s only 10-15 minutes – and keep your “appointment,” just as you would a doctor’s or dentist’s appointment.
- If possible, schedule your exercise for the time of the day when you feel most energetic. But even if you’re tired, remind yourself that being active will give you more energy.
- If you’ve been inactive, start slowly and build up gradually. Perhaps start by walking just 10 minutes a day, and gradually work up to 30 minutes a day. Over time, increase your pace, e.g., from 2 miles per hour (mph) to 3-4 mph.
- Take a walk during your lunch break.
- Do outdoor activities with your children: take a walk, ride bikes, hike, or play Frisbee, volleyball, or basketball.
- Set up a regular walking time with a buddy. It’s harder to back out when someone else is involved.
- Rake leaves in the fall. Garden in the spring and summer.
The Women’s Health Study participants were bunched at the low end of activity, with few women in the higher end. Consequently, the gains comparing moderate activity to inactivity jumped out of the data. The JAMA study is the first to suggest a benefit at lower-than-recommended levels of activity, and the study’s authors caution against changing official recommendations until these findings are duplicated by others.
Still, the findings are encouraging. I-Min Lee,M.B.B.S., Sc.D., Associate Professor of Medicine, Harvard Medical School – and the study’s lead author – explains: “Our public health problem is at this low end of the spectrum of activity. If clinicians can say to women who are sedentary, ‘Just walk an hour a week,’ I think that’s relatively easy for them to accomplish. Once they reach this level, they’re more physically fit and more confident in their ability to exercise. I wouldn’t stop there, at least based on this one study. I would encourage them to go beyond that, to gradually do more, so that they reach the level of 30 minutes of moderate-intensity physical activity on most days of the week that meets current recommendations.
“The study’s finding that one hour a week of walking reduces heart-disease risk among inactive women doesn’t mean that physically active women should relax their efforts. The study’s more active women were less likely to be overweight, or to have hypertension, elevated cholesterol, or diabetes. Other research looking at risk factors suggests that the more you do in terms of activity and intensity, the better off you’ll be. But women who previously engaged in no physical exercise will enjoy the greatest gains by simply starting some physical activity – such as one hour of walking per week.