Well: For Fitness, Intensity Matters

Phys Ed

Gretchen Reynolds on the science of fitness.

This year, exercise science expanded and fine-tuned our understanding of how physical activity affects our brains, joints, hearts, and even genes, beginning before birth and continuing throughout our lifespans, which can be lengthened, it seems, by exercise, especially if we pick up the pace.

This year's fitness news, as a look back through 2013's Phys Ed columns shows, was variously enlightening, validating (if, like me, you never bothered cooling down after a workout anyway), and practical (D.I.Y. concussion testing, anyone?). It was also occasionally deflating, at least if you hoped that barefoot running invariably would reduce the risk of injury, gentle exercise would quash your appetite, or training for a marathon would automatically exempt you from being a couch potato.

But the lesson that seemed to emerge most persistently from the fitness-related studies published this year was that intensity matters, especially if you wish to complete your workout quickly. The most popular column that I wrote this year, by a wide margin, detailed "The Scientific 7-Minute Workout," a concept that appealed, I have no doubt, because the time commitment was so slight. But the vigor required was considerable; to gain health benefits from those seven minutes, you needed to maintain a thumping heart rate and spray sweat droplets around the room.

Almost halving the time spent exercising was also effective, a later and likewise popular column showed. In that study, out-of-shape volunteers who ran on a treadmill for a mere four minutes three times a week for 10 weeks raised their maximal oxygen uptake, or endurance capacity, by about 10 percent and significantly improved their blood sugar control and blood pressure profiles.

The results undercut a common excuse for skipping workouts. "One of the main reasons people give" for not exercising is that they don't have time, said Arnt Erik Tjonna, a postdoctoral fellow at the Norwegian University of Science and Technology, who led the study.

But they emphasize, too, the potency of hard effort. The volunteers ran at 90 percent of their maximum aerobic capacity for those four minutes, a level that is frankly unpleasant. But, in four minutes, they were done.

There were other hints throughout the year that exerting yourself vigorously may have unique payoffs, compared with less strenuous exercise. In a study that I wrote about a few weeks ago, for instance, people who walked briskly, at a pace of 17 minutes per mile or less, generally lived longer than those men and women who strolled during their walks, at a pace of 20 minutes per mile or slower, although the study was not designed to determine why the intensity of the exercise mattered.

And in September, I wrote about two studies showing that strenuous exercise blunted volunteers' appetites after workouts more effectively than longer sessions of easy exercise did. The studies were small, though, and involved only young-ish, overweight men. Whether the results are applicable to other people, including those of us who are not male, requires additional experiments. I expect to be covering the results in 2014.

Meanwhile, other studies that I wrote about this year emphasize how pervasive the impacts of any amount and type of exercise can be. One of my favorite experiments of 2013 detailed how rodents that ran on wheels for several weeks responded far better to stressful situations than sedentary animals, in large part, it seems, because their brains contained specialized cells that dampened unnecessary anxiety. At a molecular level, the runners' brains were calmer than those of their sedentary lab mates.

But perhaps the most remarkable studies of the year examined the effect of exercise on our DNA. In several experiments, which I wrote about in July, scientists found that exercise reshapes genes in human cells, changing how atoms attach to the outside of individual portions of our DNA. As a result, I wrote, the behavior of the gene changes. In one of the studies, researchers found that six months of moderate exercise profoundly remodeled genes related to the risk for diabetes and heart disease. But for those of us too impatient to wait six months, the other study found that a single session of bike riding altered genes in volunteers' muscle cells. The effects showed up whether the pedaling was easy or strenuous, but, in line with so much of this year's exercise science, were more pronounced when cyclists rode vigorously.

Still, for everyone, as one of the scientists told me, the studies are an important and inspirational reminder of "the robust effect exercise can have on the human body, even at the level of our DNA."

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