A 79-year-old man picked up an object with his left hand and suddenly felt a sharp pain in his shoulder. Something moved in his upper arm. And with that, he was Popeye.

His right arm looked the same as it always had: lean and sagging a little with age. But his left biceps now sported a baseball-size bulge that looked like it could land a powerful punch. The brand-new muscle mound looked even bigger when the man flexed his biceps. The only thing was, it hurt. A lot.

He had not eaten an inordinate amount of spinach that day, nor was he a one-eyed sailor man. But as the man's doctors wrote Wednesday in The New England Journal of Medicine, he had a condition called a Popeye deformity.

MRI showed that the new lump was, in fact, his biceps. In picking up the object, the man had ruptured a tendon that connected the biceps to his shoulder. Tendons keep the springlike muscle stretched from shoulder to elbow. When it tore, the biceps sprang free, settling toward the elbow.

"It becomes like a ball," says Dr. Nabil Ebraheim, an orthopedic surgeon with the University of Toledo who sees patients with Popeye deformity every so often.

This injury is more common in people over the age of 50, when tendons, muscles and ligaments can weaken after years of wear. Often, doctors will just leave it be.

"The older guys like it," says Ebraheim. "They come and flex their muscles."

He says the injury is painful at first, but often the pain subsides after a few weeks. In fact, sometimes surgeons will purposefully cut the tendon, causing Popeye deformity, to relieve patients of persistent shoulder pain.

"Sometimes doctors do it to help the patient," says Ebraheim.

In other patients, though, cramping can be a real problem.

"There are many patients that are quite bothered by it. It's like a charley-horse-type pain in the arm," says Dr. Peter Millett, an orthopedic surgeon and shoulder specialist at The Steadman Clinic in Colorado.

A few years ago, Millett started surgically repairing Popeye deformities, which aren't always so obvious, in patients with chronic pain by reattaching the tendon to the bone.

In this case, the doctors just prescribed the man some anti-inflammatory drugs. Four months later, the pain didn't bother him anymore. And maybe he'd gotten used to looking like Popeye.

Rae Ellen Bichell is a science journalist based in Colorado. She previously covered general science and biomedical research for NPR. You can find her on Twitter: @raelnb

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