Harvard Health Letter

Why we should exercise - and why we don't

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.

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