Is Exercise Good for Your Health?

This may sound like a stupid question, but it's one that I've often wondered about. Here's a post in which Greg Mankiw shares his thoughts:

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I have long wondered whether exercise passes a cost-benefit test. That is, if one does not enjoy exercise for its own sake, does it yield benefits that outweigh the costs?

[A] serious issue is the identification problem. This was aptly summarized in a letter to the Times…

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If those who run regularly are less likely to have a heart attack, does that prove that running regularly is good for the heart? Or does it simply indicate that those with a strong heart and good health otherwise are more likely to enjoy running and do it more regularly? Your advice is probably right. But to know for sure is probably one of the most difficult problems in epidemiology. It would require telling one randomly selected group, ''You run,'' and another similarly selected group, ''You be a couch potato.'' Tricky to organize and tricky to avoid defectors' messing up the study.

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Absent a controlled experiment, it is hard to know if vigorous exercise is the cause of good health, or good health is the cause of vigorous exercise.

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I think it is vital to keep yourself physically and mentally active during your lifetime and to eat a balanced and nutritious diet, maintaining a healthy weight. However, I'm not convinced that vigorous exercise on a routine basis adds that much health value (and may actually have a negative impact beyond a certain level -- think of sports injuries and lifelong complications that can arise from them). Like anything else, the health benefits of exercise are subject to the law of diminishing returns.

Of all the people I know who have lived in good health into their 80s, 90s or 100s, I don't know of a single one who were "exercise-a-holics" in their younger years. What seemed to be more common was a continued interest in the world and people around them, well connected relationship, a good sense of humor, and religious belief. I should note that most of these people did grow up on farms and did physically demanding work in their younger years, so that may factor in. (I just got back from a trip to Alaska with my 90-year-old Aunt Ruth and she was able to get around just about as well as anyone on our tour.)

While I certainly wouldn’t use this as a reason not to exercise, it does give one pause to realize just how little we know about such a simple question as: “Is exercise good for your health?”