For his part, Ball doesn’t seem to have much trouble maintaining perspective.

“It’s always funny to me because they’re like, ‘Ugh, my Achilles’ hurts,’” Ball said. “OK, well, they cut part of my eye out last week. Everybody’s got their problems.”

Ball grew up in Davenport, Iowa, where his father coached football and his mother, Jan, was a chiropractor. Tim O’Neill, one of his closest friends, recalled that Ball was intelligent and athletic — the fastest kid in the neighborhood. Ball thought he would play college basketball, until his 3-point shot evaporated when he was in high school.

“I couldn’t see the hoop,” he said.

Diagnosed with keratoconus, the gradual thinning and bulging of the cornea, Ball abandoned his wayward jump shot to run track at Arizona State, where he learned the hard way what it’s like to run with nagging injuries. Before his senior year, he left school because of a family emergency and wound up studying for his chiropractic degree in his hometown.

“I wanted to be really good at something,” Ball said, “and when I found this, I probably did become slightly obsessive.”

He returned to Arizona and opened his own practice, seeing regular people with regular problems. His favorite patient, he said, was an older woman with carpal tunnel syndrome who knitted him a blanket.

His career changed in the run-up to the 2004 Olympics, when he met Patrick Nduwimana, an N.C.A.A. champion in the 800 meters while at the University of Arizona. Nduwimana, who was recovering from ankle surgery, said a friend had recommended Ball as a practitioner of “active release therapy,” a form of manual chiropractic treatment. For about an hour, Ball applied pressure using his hands on Nduwimana’s ankle as a way to release tension.

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