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Phys Ed Gretchen Reynolds on the science of fitness.

Tens of thousands of Americans sprain an ankle every year. But ankle sprains get little respect, with most of us shrugging off the injury as inconsequential and soon returning to normal activities.

Several new studies in people and animals, however, suggest that the effects of even a single sprained ankle could be more substantial and lingering than we have supposed, potentially altering how well and often someone moves, for life.

Healthy ankles are, of course, essential for movement.

“The ankle is the base of the body,” said Tricia Hubbard-Turner, a professor of kinesiology at the University of North Carolina at Charlotte, who led the recent studies. “Everything starts with the ankle.”

But the ankle can be surprisingly fragile and vulnerable to clumsiness (or maybe that’s just me). Step awkwardly off a curb, slide off your high heels, plant a foot wrong while running or playing a sport, and you overstretch or tear the ligaments around the joint and sprain your ankle.

Until recently, few of us worried much about the injury, assuming in most cases that the sprain would fully heal within a week or two, with or without medical attention.

But three new studies, each co-authored by Dr. Hubbard-Turner, raise serious questions about whether ankle sprains are really so benign.

In the most worrying, since it involves young people, she and her colleagues recruited 20 college students with chronic ankle instability — a condition caused by ankle sprains, in which the ankle easily gives way during movement — and 20 healthy students and asked all of them to wear a pedometer for a week. The researchers controlled for variables like sex, B.M.I. and general health.

It turned out that the students with chronic ankle instability moved significantly less than the other students, taking about 2,000 fewer steps on average each day.

That finding echoed the results of an earlier study by Dr. Hubbard-Turner, although that experiment involved young adult mice. For it, the researchers mildly sprained some of the rodents’ ankles by surgically snipping one of the ligaments on the outside of the joint. They more severely sprained other animals’ joints by snipping two of the ankle ligaments; and performed sham surgery on others to serve as a control group.

Then they let the ligaments heal for several days before giving all of the animals access to running wheels and also testing them for balance by inking their feet and having them skitter along a narrow beam. The researchers could track slips by noting where the colored footprints had slipped off of the beam.

The researchers followed the mice for a year.

At the end of that time, the mice that had undergone sham surgery — whose ankle ligaments had remained untouched — were running significantly more mileage on their wheels than the mice that had had sprains, especially those that had had a severe sprain, even though, presumably, the injury had healed long ago.

The animals with past sprains also continued to slip during balance testing far more often than the control mice. Their balance was impaired and, the researchers concluded, about 70 percent of the mice from the sprain groups had developed the rodent equivalent of chronic ankle instability as a result of a single past sprain.

This animal study and that of the college students were relatively short-term, however. Although mice may be approaching rodent retirement age after a year, that span does not generally represent their entire life, and the researchers wondered whether the past ankle sprain might turn out to affect their life-long movement patterns.

So for another study, this one published last month in The Journal of Sports Science and Medicine, they continued to follow and test the same groups of mice until they passed away from old age, usually within an additional 12 months.

They found that the repercussions of a single ankle sprain lingered throughout the animals’ lives. The mice that had experienced a mild sprain in young adulthood generally continued to run less and more slowly throughout their lives than the animals that had undergone sham surgery, and those that had experienced a severe ankle sprain ran even fewer miles and at the slowest speeds.

“In these animals, a single sprain had led to far more inactivity” throughout their lives than among the animals with intact ankles, Dr. Hubbard-Turner said.

Of course, these were mice, not humans, so it’s impossible to know whether the same decline in lifelong activity occurs in people who sprain an ankle.

But that possibility implies that we should take sore ankles seriously, Dr. Hubbard-Turner said.

“Don’t ignore a sprain,” she said.

If you twist or otherwise hurt your ankle, consult a doctor or physical therapist about diagnosis, treatment and rehabilitation. And if you have sprained an ankle in the past, even if the injury seems fully healed, consider balance testing by a physical therapist to determine whether you are more wobbly than you suspect.

Finally, if you have never sprained an ankle, pat yourself on the back, preferably while standing on one leg. “Balance training is a good idea for everyone,” Dr. Hubbard-Turner said. (This video has useful balance training tips here.)

The best way to avoid the consequences of a sprained ankle, she said, “is to not sprain it in the first place.”



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