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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Healthy Heart Healthy Heart

How Much Exercise Is Enough?

June 27, 2013

By Thomas H. Lee M.D.

Harvard Medical School

Last reviewed by Faculty of Harvard Medical School June 27, 2013

Everyone should exercise for 20 minutes three times per week. No, make that five times per week for 30 minutes. No, make it more like an hour every day. No, scratch that — short bursts of intense activity for 10 minutes at a time, a few times a day.

You hear so much contradictory information about exercise, it's hard to know what to believe. No wonder so many people tune out completely, and go back to surfing the Net or watching TV. A logical conclusion might be that researchers do not know what they are talking about. Actually, the situation is much worse — all of those seemingly contradictory recommendations are probably true.

In actuality, you only need to do gentle activities like walking and gardening to lower your risk of heart disease. Below is a quick guide to what constitutes a reasonable prescription for exercise:

  1. If you aren't doing much physically, then mild exercise a few times a week will cut your heart disease risk in half. Americans have become incredibly sedentary — remote controls, drive-up banks, elevators and other conveniences have made it possible to get through the day burning a trivial amount of calories. As a result, even mild activity — like walking at a reasonable clip — a few times per week can make a big difference in the health of your blood vessels. Just raising your heart rate and dilating those arteries modestly can help to lower your blood pressure and fight off atherosclerosis. So, if you are a true couch potato, the orders from this doctor are to begin doing 20- to 30-minute walks three days a week. If you feel chest pressure, light-headed or markedly short of breath, see your doctor right away. But if not, get back out there in two days.
  2. If you do mild exercise a few times a week, increase the frequency to every day. At this point, we know it is safe for you to take those one- to two-mile walks. So what's the point of waiting two days before your next one? Going to daily exercise will help you to burn more calories, and that will have a whole range of beneficial health effects.
  3. If you can do mild or moderate physical activities daily, start doing short bursts of more intense activity. You can jog five or 10 miles per day at the same slow clip, and you will burn plenty of calories, but you won't really make your cardiovascular system much healthier. One of the painful messages from recent research is that intense activity — 30 to 60 seconds of really pushing yourself — takes the health of your blood vessels to a new level. This kind of interval training is what athletes do, and for good reason. It conditions your arteries to pump out nitric oxide and other chemicals that help them dilate when your muscles really need a lot of blood. And there is pretty good evidence that this kind of stress on the arteries helps to keep them younger.

Naturally, you should not increase your activity level if you feel any of the warning symptoms described above. Those are good reasons to stop, rest and give your physician a call. But the bottom line on exercise is that whatever you are doing, try doing more. If you are burning a lot of calories with long bouts of exercise, you should try exercising more intensely for shorter periods.

It takes discipline to constantly move to a higher level of exercise. Sometimes working with a trainer or going to an exercise class can help. In the meantime, consider these recommendations a doctor's orders.

Thomas H. Lee, M.D., is the chief executive officer for Partners Community HealthCare Inc. He is a professor of medicine at Harvard Medical School. He is an internist and cardiologist at Brigham and Women's Hospital. Dr. Lee is the chairman of the Cardiovascular Measurement Assessment Panel of the National Committee for Quality Assurance.


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