Ross Martinson once felt invincible.

One of those high-velocity land animals, he could run nearly forever and fast, finishing 23d in the Boston Marathon and three times in the top five of the Broad Street Run.

Then, in 2008, he ran the Rock 'n' Roll distance run, finishing the half-marathon in 1 hour 6 minutes and 49 seconds.

As he walked off the course, he felt some tightness in his calves. Two hours later, he was crippled with pain.

"It felt like I was screwed up," he said with a runner's classic understatement.

The injury, a damaged Achilles tendon, would put an end to Martinson's competitive running career. Not because of the initial insult, but because it has taken him five years to discover how to properly treat the problem.

If he knew then what he knows now, he said, "instead of working in the marathon last week, I would have been competing in it at a high level."

Achilles tendinopathy is one of the most common problems for runners, accounting for an estimated 6 to 18 percent of the sport's injuries.

Physical therapists, podiatrists, orthopedic surgeons, and foot and ankle specialists report that several weeks after a marathon, they invariably find more patients limping into their offices.

The delayed search for treatment has more to do with psychology than physiology, said Karin Silbernagel, assistant professor of physical therapy at the University of the Sciences whose work is funded by the Swedish Center for Sports Research.

Just after a race, athletes expect to feel aches and pains, said Silbernagel, 48, who specializes in the Achilles tendon.

"But it's after they start building back up, doing longer training runs again, that they realize the problem isn't going away."

The Achilles is a thick tendon running down the back of the calf and attaching to the bone above the ankle. For decades (except in cases where it had clearly ruptured), patients complaining of pain in the tendon were believed to be suffering from acute inflammation, or tendinitis.

They were told to rest and stay off their feet.

In most cases, that turned out to be exactly the wrong treatment, said Silbernagel. For as research in the late 1990s showed, most Achilles injuries are degenerative, a breakdown in the tissue. And for that, she said, the remedy is exercise.

"We learned we need to load the tendon in order to heal it."

Since a damaged Achilles tendon may feel tight, the inclination is to try to stretch it. That can worsen the problem, especially when the damage occurs at the lower point where the tendon attaches to the bone.

A healthy tendon has long, straight fibers. When it breaks down, the tissue shreds and tatters, much like a cut rope.

"When you get up in the morning, it hurts. Adhesions form while you sleep," said Howard Palamarchuk, director of sports medicine at Temple University's School of Podiatric Medicine. "When you stretch, you create little tugs and tears."

The recent barefoot running fad led to a rise in Achilles injuries, he said.

He agrees with Silbernagel that a careful balance must be found between stretching and strengthening.

She has always been interested in exercise and understands the mentality of elite athletes. Two of her three brothers competed in the 1984 Olympics on the Swedish sailing team.

When the subject turns to tendons, Silbernagel starts talking with greater speed and intensity.

"I love the complexity of the foot," she explained. "We underestimate its capacity. We try to pacify it, put it in shoes."

She picked up a plastic model of a lower leg, ankle, and foot and demonstrated how, with each step, a slackened tendon presses against the underlying bursa and bone before lifting the heel.

The cure, she said, is to strengthen the calf muscle.

Until recently, the prescription has been to give everyone the same set of "eccentric" exercises - essentially rising up on the toes and slowly lowering the heels. This challenges and strengthens the muscles and tendons.

Lately, though, clinicians have been wondering if the one-size-fits-all model needs to change.

"If exercise is medicine, dosage is crucial," Silbernagel said. "Right now, we have one dose for all." But an elite athlete, for whom a five-mile jog feels like no exercise at all, may not heal the same way as someone who can barely climb a flight of stairs.

Before starting care, Silbernagel asks her patients to see how many times, keeping up with the pace set by a metronome, they can rise up on the ball of each foot and lower down.

The average person can do about 20 repetitions before exhausting the calf muscle.

On his first try, Martinson managed 45.

For a typical person, that kind of calf strength would be impressive. "But not for the demands I was putting on it," he said.

Before finding Silbernagel, Martinson had seen a host of doctors and physical therapists and tried almost every remedy, short of surgery. He had rested. Iced. Taken ibuprofen. He had been massaged and adjusted and X-rayed.

"Nobody could really tell me what was going on," he said. "I was beginning to think it was all in my head."

Martinson, 35, is co-owner of the Philadelphia Runner stores, a running coach, and elite runner coordinator for the Philadelphia Marathon and Broad Street Run. For a few years, he kept running through the pain, even finishing a few races. But by last spring, he had given up.

"I didn't think I would ever run again. There would be mornings that I'd get out of the car and hobble the three blocks from the parking garage. I definitely didn't look like any sort of runner."

Months before, a friend had told him that Silbernagel was a wizard with these injuries. In June, he finally made an appointment.

She did an ultrasound and showed him the shadowy image.

"She pinpointed the spot in your tendon where it's really messed up," he said. "You can see the tissue that's healthy, there are straight lines across. It looks significantly different from this area on the bone side just above my heel - it looked like a darker jumble of tissue."

He started doing the exercises. After a couple of months, she had him start running again, giving himself four days to recover, then gradually cutting back to three.

"It's definitely been an incredibly frustrating injury," he said. "When I first went in to see her, I asked, 'Is it ever going to get better?' "

"Yes," Silbernagel said. "It might take a while, but we can get you running again."

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