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Sometimes it’s good news when a study’s hypothesis is not proved. That was the case, certainly, with a new study of older runners, in which researchers assumed that athletes over 60 would be noticeably less efficient than their younger counterparts.

For the experiment, published in The Journal of Strength and Conditioning Research, researchers at the University of New Hampshire and other institutions recruited 51 competitive runners, ranging in age from 18 to 77. Each trained regularly and had placed in the top three in his or her age group in a local 5-kilometer or 10-kilometer road race. Their goal was to assess running economy, a measure of how much oxygen someone uses to run at a certain pace. Economical runners can continue at a given speed longer than inefficient striders, outdistancing them.

Going into the study, the researchers had assumed that runners past age 60 would be less economical than youthful athletes, since older runners, as a group, are slower than younger ones. But as it turned out, when scientists fitted the volunteers with masks that measured their oxygen use as they ran on a treadmill and then compared the results by age group, the runners 60 and older were just as physiologically economical as younger runners, even those in their 20s and 30s.

“It was quite a surprise,” said Timothy Quinn, a professor of exercise science at the University of New Hampshire and lead author of the study. “Economical runners perform better than less-economical runners. And contrary to our expectations, economy did not decline with age.” The results are encouraging for older runners, he continued, suggesting that aging lungs and leg muscles have no trouble using oxygen efficiently, and that older runners can still be fast.

Masters runners and, in particular, those 60 and older are the fastest-growing group in the sport, according to most statistics. A recent study of the New York City Marathon from 1980 to 2009, for example, found that “the percent of finishers younger than 40 years significantly decreased, while the percent of masters runners significantly increased for both males and females,” said Romuald Lepers, a professor of sports sciences at the University of Burgundy in France who, with his colleague Thomas Cattagni, conducted the study.

In the coming weeks, thanks to New Year’s resolutions, many more of us are likely to swell the ranks of well-seasoned runners.

But science is only starting to systematically study older runners, and not everything that is being learned is encouraging. For instance, a sobering examination of running injuries, published in Current Sports Medicine Reports, found that middle-aged and older runners are much more prone to problems with Achilles tendons and hamstring and calf muscles than their whippersnapper counterparts. A possible explanation for the high rate of such injuries among the post-40 set, the study authors speculate, is that the normal muscle wear and tear “that occurs with training seems to take greater time to repair with aging, and older runners continue running at a frequency similar to that of younger runners.”

So much for age conferring patience and wisdom.

Dr. Quinn’s group, too, found that some physiological parameters did worsen with age. Older runners scored poorly on tests of upper-body strength and lower-body flexibility, both of which can affect the ability to compete.

“You need upper-body strength to pump your arms and generate power and velocity, especially on hills,” Dr. Quinn said. Similarly, flexible tendons and muscles in the lower leg allow full, easy strides. “We didn’t measure step length,” he said, “but my guess is that it was shorter” among the runners who were 60 or older. With tighter tissues, older runners are constrained to choppy strides and, in general, a slower pace.

Happily, Dr. Quinn says, these particular physical detriments can be improved. “Older runners should try very hard to get to the gym to lift weights a few times a week,” he said. Concentrate on exercises that build upper-body strength. The sexagenarian and older runners in his study had almost as much leg strength as younger runners, he says, but far less muscle mass, strength and power in their arms and shoulders.

Stretch occasionally after a run, too, he advises. It’s not as clear that flexibility aids in running performance among older runners, he says. But to help maintain speed, “it’s probably not a bad idea to work on lower-body flexibility, especially if you used to be more flexible.”

Should you need further inspiration, consider another finding of the study of older New York City marathon racers. The researchers report that in recent years, the average finishing time for the fastest men 60 and older dropped by more than seven minutes; among older women, it plummeted by more than 16 minutes. And the improvements show no sign of slowing. Older runners “have probably not yet reached their limits in marathon performance,” Dr. Lepers says, which is worth bearing in mind as you set your 2012 exercise goals.