Animal data comprehensively demonstrates that regular exercise improves long-term health. The data on life extension is less conclusive, but in some studies more individuals lived into what is the late life period for their species, extending mean life span. Other studies show no such increase. Researchers can follow groups of animals for their entire life spans and crunch the numbers: the causality of results can be well demonstrated, and we can safely conclude that exercise is producing these benefits.
In human studies statistics and population surveys have to substitute for following groups carefully segregated by amount of exercise, with scientific controls and consistent data gathering, for an entire life span. It is very hard to pull causality from this sort of data, but the data itself looks very similar to that generated in animal studies, in that regular exercise is a good thing for health and produces analogous short term changes in measures of metabolism. It isn't unreasonable to expect on the basis of all this evidence that regular exercise does indeed cause better health, on balance, across populations, in humans just as it does in animals.
All this has been said numerous times, and there are mountains of data to support it. You should be exercising, as your physician no doubt reminds you on every occasion that the two of you meet: it costs little and produces greater benefits for most people than any sort of presently available medical technology. There is so much epidemiological data on exercise available in this age of cheap computing that anyone with the time and skills can slice and dice it to come up with new measures - such as a guesstimate of the return on investment for exercise. What is the expected outcome in terms of time gained versus time invested? This will not be a simple linear relationship, but it is interesting to come up with simple speculative numbers - and bear in mind that it isn't just life gained, but also medical expenditures and pain and suffering reduced:
It's a daily struggle to make the time to exercise, and the current federal health guidelines call for at least 150 minutes a week of moderate exercise - a lot of time that somehow manages to seem like even more, magnified by the "should" it adds to so many days. There are hundreds of other reasons to exercise, and the one that works best for me is wanting to feel at my best on that very day. But it would be very comforting, I thought, if I knew that all of that time would come back to me.
Let me cut to the happy conclusion: It seems that it does. And then some. If you play with the data of a recent major paper on exercise and longevity, you can calculate that not only do you get the time back; it comes back to you multiplied - possibly by as much as seven or eight or nine.
Pooled data from six large studies that included more than 650,000 people followed over ten years [showed] that people who exercised at the recommended level gained 3.4 years of life after age 40. Say you start with someone 45 years old who begins to follow the 150-minute-a-week recommendation. Average American life expectancy is 78. So: "If you start exercising at 45 and you die at 78, that means that you exercise for 33 years, at 150 minutes a week. I calculated that over 33 years you would need to spend basically 4,290 hours in exercise, which is 179 days of exercise, which is less than half a year. So that's half a year, and you gain almost three and a half years, so it is worth exercising. That's an approximate scenario using reasonable assumptions, and you're getting a 1-to-7 return.
On the flip side of the coin, there is the now fairly established ballpark estimate that being sedentary is about as bad as smoking when it comes to the bottom line of whether you are going to be alive or dead or dying some number of years from now:
People across the world are falling so far short on exercise that the problem has become a global pandemic, causing nearly a tenth of deaths worldwide and killing roughly as many people as smoking, researchers warned this week. Eight out of 10 youngsters age 13 to 15 don't get enough exercise [and] nearly a third of adults fall short. The problem is even worse for girls and women, who are less active than boys and men, researchers found.
The results are fatal. Lack of exercise is tied to worldwide killers such as heart disease, diabetes and breast and colon cancer. If just a quarter of inactive adults got enough exercise, more than 1.3 million deaths could be prevented worldwide annually, researchers said. Half an hour of brisk walking five times a week would do the trick.