How Much Exercise Is Enough?

The Institute of Medicine's new stand on physical activity succeeded in one sense -- it sure raised a few heart rates.

The private advisory group's call for 60 minutes of physical activity each day are in line with the 2005 USDA Guidelines for exercise of 30 to 60 minutes on most days of the week. The new advice was meant to get people moving, but some experts are worried about recommending 60 minutes.

"The concern is that individuals will see this call for 60 minutes and think, 'My gosh, now it's 60 and I can't even do 30,'" says Edward T. Howley, Ph.D., president of the American College of Sports Medicine. "Sedentary individuals might be dissuaded from physical activity altogether."

But scientists who came up with the advice say the dispute is an exercise in confusion.

The Institute of Medicine (IOM) is part of the National Academy of Sciences, created by the federal government to act as an independent adviser on scientific matters. In a study on diet, an IOM panel looked at the number of calories thousands of people burn each day. It found that folks with a healthy body weight take part in about an hour of activity a day while sticking to a sensible diet.

The panel measured all calories burned -- everything from low-intensity movement such as climbing stairs to high-intensity exercise such as tennis. So the recommendation isn't based on a solid hour of exercise. You can count short sessions through the day with varied intensity levels. The standard, though, is 60 minutes total of moderately intense activity, such as walking 3 to 4 miles per hour.

"People are confusing physical activity with exercise," says IOM panel member George Brooks, Ph.D., a professor of integrative biology at the University of California at Berkeley. "If you walk to work, if you use the stairs, that is physical activity. If you go for a half-hour run, that's vigorous exercise, and it will be about the energy equivalent of walking briskly for an hour. So it's really a refinement of the Surgeon General's report."

The 60-minute advice is aimed at improved health and weight control. It does not rule out health benefits from lesser levels of activity. Studies show that 30 minutes of moderate activity a day lowers your risk of heart disease and diabetes.

If you're sedentary, 30 minutes of moderate activity is a good goal, says I-Min Lee, Sc.D., associate professor of medicine at Harvard Medical School. She found in one study that as little as an hour of walking a week halved the heart disease risk in a group of sedentary, middle-aged women. Still, she recommends more than that. "Thirty minutes of moderate activity per day still represents the low end of the scale, which should be the goal if you are sedentary."

So your needs depend on your goals:

  • If you want to keep your heart healthy and help fend off diabetes, 30 to 60 minutes of moderate activity most days of the week should do.

  • If you want to reap those benefits and watch your weight, follow the 60-minute advice.

  • If you want to lose weight, you must exceed the 60-minute level, or keep up that activity level while taking in fewer calories.

Any movement that raises your heart rate counts. To burn more calories, try higher-intensity activities like jogging or swimming.

Don't let confusion keep you on the couch. "Some people might say, 'I'm not going to exercise until [the scientists] get it right,' and that's not what we want," Dr. Lee says.

Get the lead out

You can build physical activity into sedentary situations.

• Desk jobs: Take the stairs, not the elevator. Walk to a co-worker's office rather than phoning. Take a walk (10 to 30 minutes) during your lunch hour. Get up, stretch and move at least once an hour.

• Autos: Walk instead of driving for short trips. When driving, park farther away from your destination instead of looking for the closest parking space. Wash the car yourself rather than using an automatic car wash.

• TV: Work out on a stationary bike or treadmill while you watch. Replace a half-hour of viewing each day with exercise or exercise while viewing a favorite program.

Burning calories

Calories burned in half an hour by a 150-pound adult:

Basketball 288

Gardening 162

Golf (no cart) 198

Raking lawn 162

Running (11.5 min/mile) 324

Step aerobics 252

Swimming 216

Tennis 252

Walking (3.5 mph) 144

Washing car 162

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