Why we should exercise - and why we don't

If the benefits of physical activity are legion, so are the reasons for avoiding it. We've got suggestions for adding some to your day.

You already know that exercise is good for you. What you may not know is just how good — or exactly what qualifies as exercise. That's what this issue of the Health Letter is all about. The notion that physical activity helps keep us healthy is very old news indeed. Hippocrates wrote about the dangers of too little activity (and too much food). Tai chi, an exercise system of graceful movements that originated in China, dates from the 12th century B.C. Yoga's roots in India go back much further.

But old ideas aren't necessarily good ones, or have much evidence to back them up. This isn't a problem for exercise — or physical activity, the term many researchers prefer because it's more of a catchall. A deluge of studies have documented its health benefits. Many are observational, which always pose the problem of showing associations (people who exercise happen to be healthy) not proof of cause and effect (it's the exercise that makes those people healthy). But after statistical adjustments, these studies suggest that the connection between exercise and health is more than just an association. Besides, results from randomized clinical trials, which are usually seen as making the case for causality, also point to exercise making people healthier.

What's impressive about this research, aside from the sheer volume, is the number of conditions exercise seems to prevent, ameliorate, or delay.

We're used to hearing about exercise fending off heart attacks. The American Heart Association promulgated the country's first set of exercise guidelines in 1972. And it's not hard to envision why exercise helps the heart. If you're physically active, your heart gets trained to beat slower and stronger, so it needs less oxygen to function well; your arteries get springier, so they push your blood along better; and your levels of "good" HDL cholesterol go up.

It's also not much of a surprise that physical activity helps prevent diabetes. Muscles that are used to working stay more receptive to insulin, the hormone that ushers blood sugar into cells, so in fit individuals blood sugar levels aren't as likely to creep up.

But exercise as a soldier in the war against cancer? It seems to be, and on several fronts: breast, colon, endometrial, perhaps ovarian. The effect of physical activity on breast cancer prevention may be stronger after menopause than before, although some research suggests that it takes quite a lot to make a difference: four to seven hours of moderate to vigorous activity a week. Three studies have found that if you've had colon cancer or breast cancer, physical activity reduces the chances of it coming back.

To top things off, moving the body seems to help the brain. Several studies have found that exercise can reduce the symptoms of depression, and it changes the brain in ways similar to antidepressant medications. In old age, physical activity may delay the slide of cognitive decline into dementia, and even once that process has started, exercise can improve certain aspects of thinking.

Easy to avoid

We have to eat, so following nutritional advice is a matter of making choices. Swap out the trans for the unsaturated fats. Eat whole grains instead of refined carbohydrates.

But in this day and age, many (perhaps most) people don't need to be physically active unless they choose to be. And most evidence suggests that the choice of the kind of activity is far less important than whether to be active at all. About half of adult Americans don't meet one of the most oft-cited guidelines, which calls for 30 minutes of moderate-intensity activity (a fast walking pace) most days of the week — and you can accumulate that total in bouts of 10 to 15 minutes. The number of hard-core nonexercisers has stayed pretty stable since the late 1980s. About a quarter of American adults say they devote none of their free time to active pursuits.

Clearly some of us are less athletic than others — and some unathletic individuals were simply born that way. Twin studies suggest that about half of the difference in physical activity among people is probably inherited. And researchers are making headway in identifying particular genes that may influence how we respond to physical exertion. For example, they've identified some of the genes responsible for variation in the beta-agonist receptors in the lungs. How your lungs and heart react to strenuous exercise depends, in part, on those receptors.

But genetic explanations for behaviors like exercising only go so far. Many other influences come into play: family, neighborhood, cultural attitudes, historical circumstances. Research has shown, not surprisingly, that active children are more likely to have parents who encouraged them to be that way. Perceptions of how active parents are also seem to matter. The safety and layout of neighborhoods is a factor, particularly for children. In a dangerous place, having children stay home and watch television instead of going to the park to play might be the healthier choice simply because it's safer.

The types of activities offered to people make a difference, too. Researchers at San Diego State University reported results in 2008 of a study that offered sedentary, low-income Latino women aerobic dance classes at storefront exercise sites three times a week. At the end of the six-month study, the dance sessions resulted in a fivefold improvement in their maximal oxygen uptake, an important measure of fitness.

Illness and disability sometimes get overlooked as obstacles to activity, and they are bound to become more important as the American population ages. In 2006 Researchers at the National Cancer Institute subdivided people identified as sedentary by a national survey into eight subgroups based on their health, education level, whether they believed that exercise prevented cancer, and a number of other factors. The most sedentary of all was the subgroup they called "illness-burdened couch potatoes": people in poor to fair health with some college education who watched over four hours of television on a typical weekday.

The trip of a thousand miles begins...

As we went to press with this issue, the federal government was scheduled to release new physical activity guidelines sometime in October 2008. The scientific committee that advised the guideline writers concluded that current research supports the standard advice to get 30 minutes of moderate-intensity exercise most days of the week. We're also supposed to do exercises to build up muscle strength twice a week. But the committee noted that studies show that some exercise, even if it is pretty minimal, is better than none, particularly among people who are very sedentary.

So in that spirit, we've made 27 suggestions for ways to become a little bit more physically active. Some are adapted from a book published by Sport England, a group in Britain that encourages activity and fitness. If you've got suggestions, please e-mail them to us at health_letter@hms.harvard.edu, and we'll post them on our Web site.

1. Take the far away spot. Walking from the farthest corner of the parking lot will burn a few calories. If it's a parking garage, head for the roof and use the stairs.

2. Walk to the next stop. If you take a bus or train, don't wait at the nearest stop. Walk to the next one. Or, at the end of your journey, get off a stop early and finish up on foot.

3. Hang loose. During your bus or train trip, stand and don't hold on too tightly. You'll improve your sense of balance and build up your "core" back and abdominal muscles.

4. Get into the swing of it. Swinging your arms when you walk will help you reach the brisk pace of 3 to 4 miles per hour that is the most healthful.

5. Walk and talk. If you are a member of a book group, propose 15 to 20 minutes of peripatetic discussion of the book before you sit down and chat.

6. Walk while you watch. Soccer moms, dads, and grandparents can circle the field several times during a game and not miss a single play.

7. Walk tall. Maintaining good posture — chest out, shoulders square but relaxed, stomach in — will help keep your back and abdominal muscles in shape. Besides, you'll just look a whole lot healthier if you don't slouch (mom was right).

8. Adopt someone as your walking, jogging, or biking buddy. Adding a social element to exercise helps many people stick with it.

9. That buddy might have four legs. Several studies have shown that dog owners get more exercise than the canineless.

10. Be part of the fun. Adults shouldn't miss a chance to jump into the fray if kids are playing on a playground or splashing around in the water. Climbing on the jungle gym (be careful!) and swinging on a swing will strengthen muscles and bones and set a good example.

11. Dine al fresco. Tired of eating at home? Skip the restaurant meal, which tends to be heavy on the calories. Pack a picnic. You'll burn calories looking for the best spot and carrying the picnic basket.

12. Put on your dancing shoes. Exercise doesn't have to be done in a straight line. Dancing can get your heart going and helps with balance. Dance classes tend to have lower dropout rates than gyms. Or just turn up the volume at home and boogie.

13. Wash and dry the dishes by hand. The drying alone is a mini-workout for the arms.

14. Don't use an electric can opener. It's good for your hand, wrist, and arm muscles to use a traditional opener. For the same reason, peel and chop your own vegetables and avoid the precut versions.

15. Clean house. Even if you have a cleaning service, you can take responsibility for vacuuming a couple of rooms yourself. Fifteen minutes burns around 80 calories. Wash some windows and do some dusting and you've got a pretty decent workout — and a cleaner house.

16. Hide that remote. Channel surfing can add hours to screen time. If you have to get up to change the channel, you are more likely to turn it off and maybe do something else that's less sedentary.

17. Go swimmingly somewhere. Swimming is great exercise if you have arthritis because the water supports your weight, taking the load off of joints. The humid air around a pool sometimes makes breathing more comfortable for people with lung problems.

18. Take a walk on the waterside. Even people who can't, or don't like to, swim can get a good workout by walking through the water. Try walking fast, and you'll get cardiovascular benefits. Walking in water is a great way to rehabilitate if you're recovering from an injury and certain types of surgery because the water acts as a spotter, holding you up.

19. Don't e-mail. In the office, get out of your chair, walk down the hallway, and talk to the person. At home, write an old-fashioned letter and walk to a mailbox — and not the nearest one — to mail it.

20. Stand up when you're on the phone. Breaking up long periods of sitting has metabolic benefits. Even standing for a minute or two can help.

21. Grow a garden. No matter how green the thumb, the digging, the planting, the weeding, and the picking will ramp up your activity level and exercise sundry muscles.

22. Use a push mower. Even if you have a large lawn, pick a small part of it to mow in the old-fashioned way. You get a nice workout, you're not burning any gas, and it's usually quieter. The same reasoning favors the rake over the leaf blower.

23. Think small. Small bouts of activity are better than knocking yourself out with a workout that will be hard to replicate.

24. Be a stair master. Take the stairs instead of the elevator or escalator whenever you can. It's good for your legs and knees, and your cardiovascular health will benefit from the little bit of huffing and puffing. Don't overdo. One flight at a time.

25. Stairs tip #2. You'll give the gluteal muscles a nice little workout if you can climb up two stairs at a time.

26. Stairs tip #3. You can give your calf muscles a nice little stretch by putting the ball of the foot on the stair and lowering your heel.

27. Whatever works. When it comes to physical activity, the ends do justify the means. Find something that gets you moving — and keep on trucking