Runners have a weak spot at the heel; a 2008 study cited an inflamed Achilles tendon as the most common running associated injury. That study’s authors found that an Achilles tendon overuse injury affected more than 55 percent of 291 elite runners analyzed.
The injury itself causes pain along the Achilles tendon or the back of the heel, which can feel worse in the morning, or during and after exercise, according to the American Academy of Orthopaedic Surgeons. It can also cause swelling around the tendon, and thickening or stiffness of the tendon itself, sometimes taking several months to mend.
How to prevent it:
“Training errors are the number one cause,” says Dr. Carolyn Smith, a sports medicine physician at Marquette University, and a 2010 U.S. record holder in the 12-hour ultramarathon event. Increasing mileage too quickly, adding too long of a run, or suddenly adding hills or interval training can cause Achilles tendinitis. “A foot with a very high arch can also contribute to Achilles tendinitis,” Smith says. “So can having inflexible calf muscles.”
To avoid the injury, follow a smart training progression and try this eccentric exercise to strengthen calf muscles and stretch tendons at the same time: stand on a step with your heels hanging below the step. Raise your heels up above the step, then slowly lower your heels back down. Repeat 20 times. When that gets too easy, try doing one calf at a time.