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Are modern men and women born to run, or must our 21st century bodies be carefully cross-trained to stay fit and healthy?

When it comes to care and training of the modern distance runner, expert opinions are mixed.

Jay Dicharry, author of the new book "Anatomy for Runners," believes that to be a better runner, running is not enough.

"Running is typically a one-dimensional sport," said Dicharry, a physical therapist and the director of Biomechanics at Rebound Physical Therapy in Bend, Oregon.

"You're basically just moving forward. You're not really developing as a true athlete."

As a consequence, he said, studies have shown that one third of runners are hurt every single year.

"So many runners just run," he said. "So many people look at a (fitness) magazine and say ‘I can do that.' Then they get hurt and wonder why," he said. "If we prepare ourselves we'll do a better job."

His book focuses on identifying weaknesses, with detailed tools for gait analysis, tips for injury prevention and corrective and complementary exercises that range from yoga-like toe strengtheners to core and stability work.

"What are your problems? Do you over stride? Do you have posture issues? Poor foot control?" he said. "Find out what you biggest problem is and fix it. That will improve where you are."

Dicharry said that, while many books focus on the runner's cardiovascular system, or engine, he zeros in on the biomechanical body, or chassis.

"Coaches get lots of information on how to train the heart and lungs. But we don't get enough on how to keep the body healthy," he said. "The more stable the chassis, the more efficient you can be. The book focuses on what's wrong and how to fix it."

Economy of motion

In the 30 years Robert Forster has practiced sports physical therapy in Santa Monica, California, he has treated world record holders, injured athletes and grandmothers recovering from hip surgery.

"Our bodies have evolved to run," said Forster by telephone from London, where he was working with the U.S. Olympic Track and Field team. "Our tree-dwelling ancestors had shorter legs, longer arms and shorter feet. The body actually changed to be effective at running. But we lost our ability to co-opt that economy of motion."

Forster said the current physical capacity of the average Western civilian is about 10 percent of what is possible.

"Some people can run 100 miles in a day," he said.

The most common running mistake he sees involves stride length, or the distance of the foot on the ground.

"Everyone is over striding," he explained. "You want to land under your center of gravity, or as close to it as possible. We tend to take too few steps per minute. Less time on the ground would take care of a lot of problems."

For the runner seeking greater efficiency, Forster prefers a series of running-related drills - among them arm swings that target the pendulum-like motion and knee-high drills, which he described as prancing "like a Clydesdale horse."

Dr. Lewis Maharam, medical director of the New York City Marathon and author of "Running Doc's Guide to Healthy Running," said that, while many exercises can make you more efficient, the beauty of running is that you don't need to do them.

"Running is the best sport there is. All you need is a good pair of running shoes and shorts, and out you go," Maharam said. "Cross training isn't really necessary. Professional athletes do it because it makes you faster, but the best people will tell you that a nice warm-up and a good flexibility program for your lower extremities is basically all you need."

Maharam said running is probably among the safest of sports, as long as you train smart.

"Probably a walk/run program to start," he said. "And never increase your mileage by more than 10 percent per week."

But the most important thing is the preparation.

"People get injured when they do stupid things," he said. "If you try to run a marathon without training you're going to get hurt."

In training, people might have ligament problems or little chronic issues, he added, but they are usually resolved.

"The most common injury we see at the marathon is a blister," he added.