By Gretchen Reynolds, NY Times, January , 2013
With New Year’s exercise resolutions still fresh and hopefully unbroken on this, day two of 2013, it now seems like the perfect time to review lessons of the past year in fitness science.

First, since I am habitually both overscheduled and indolent, I was delighted to report, as I did in June, that the “sweet sport” for health benefits seems to come from jogging or moderately working out for only a brief period a few times a week.

Specifically, an encouraging 2012 Study of 52,656 American adults found that those who ran 1 to 20 miles per week at an average pace of about 10 or 11 minutes per mile—my leisurely jogging speed, in fact—lived longer, on average, than sedentary adults. They also lived longer than the group (admittedly small) who ran more than 20 miles per week.

“These data certainly support the idea that more running is not needed to produce extra health and mortality benefits,” Dr. Carl J. Lavie, a cardiologist in New Orleans and co-author of the study told me. “If anything,” he said, “it appears that less running is associated with the best protection from mortality risk.”

Similarly, in a study from Denmark that I wrote about in September, a group of pudgy young men lost more weight after 13 weeks of exercising moderately for about 30 minutes several times a week than a separate group who worked out twice as much.

The men who exercised the most, the study authors discovered, also subsequently ate more than the moderate exercisers.

Even more striking, however, the vigorous exercisers subsequently sat around more each day than did the men who had exercised less, motion sensors worn by all of the volunteers showed.

“They were fatigued,” said Mads Rosenkilde, a Ph.D. candidate at the University of Copenhagen and the study’s co-author.

Meanwhile, the men who had worked out for only about 30 minutes seemed to be energized by their new routines. They stood up, walked, stretched and even bounced in place more than they once had. “It looks like they were taking the stairs now, not the elevators, and just moving around more,” Mr. Rosenkilde said. “It was little things, but they add up.”

And that idea was, in fact, perhaps the most dominant exercise-science theme of 2012: that little Things Add up, with both positive and pernicious effects. Another of my favorite studies of 2012 found that a mere 10 minutes of daily Physical Activity increased life spans in adults by almost two years, even if the adults remained significantly overweight.

But the inverse of that finding proved to be equally true: not fitting periods of Activity into a person’s daily life also affected life span. Perhaps the most chilling sentence that I wrote all year reported that, according to a large study of Western adults, “Every single hour of television watched after the age of 25 reduces the viewer’s life expectancy by 21.8 minutes.”

I am watching much less television these days.

But not all of the new fitness science I covered this year was quite so sobering or, to be honest, consequential. Some of the more practical studies simply validated common sense, including reports that to succeed in ball sports, keep your eye on the ball; during hot-weather exercise, pour cold water over your head; and, finally, on the day before a marathon, eat a lot.

But when I think about the science that has most affected how I plan my life, I return again and again to those studies showing that physical activity alters how long and how well we live. My days of heedless youth are behind me. So I won’t soon forget the study I wrote about in September detailing how moderate, frequent physical activity in midlife can delay the onset of illness and frailty in old age. Exercise won’t prevent you from aging, of course. Only death does that. But this study and others from this year underscore that staying active, even in moderate doses, dramatically improves how your aging body feels and responds.