Eric Cornell is the kind of guy who revels in his identity as a geek—someone enamored with numbers who spends his days exploring concepts like superfluidity and quantized vortices. But Cornell, 49, is no ordinary geek; in 2001, he won the Nobel Prize in Physics for creating the coldest matter ever known.

So it's no surprise that the longtime runner would employ an analytic approach to participating in his favorite race, the Bolder Boulder 10-K

, which takes place every May in his hometown of Boulder, Colorado. In 2000, after studying his race times over the previous decade, he set a goal for himself: to one day cover the 6.2-mile course in a time faster than his age. By 2004, that goal was nearly within reach when, at 42, he clocked a 50:47.

But that October, Cornell developed an ache in his left shoulder. "The first time I saw my physician, I got icepacks, ibuprofen, and a sling," says Cornell. "But the pain got worse." The next day he went to the emergency room, where doctors opened up his arm and found an alarming amount of dead tissue. His diagnosis? Necrotizing fasciitis—a potentially lethal infection known as flesh-eating bacteria. It had spread well beyond his shoulder.

"By the time they figured out the problem, it became less a question of whether doctors could save my arm and more could they save my life?" says Cornell, who by this point had slipped into a coma. In the end, doctors amputated his arm, shoulder, clavicle, and scapula. (While able to remove the infected tissue, doctors never determined how Cornell had contracted the disease.)

When Cornell regained consciousness two and a half weeks later, he was unable to stand or even sit up. He needed a tracheotomy to help him breathe; he also suffered severe pain on his legs where surgeons had removed skin to graft onto his wound. Nevertheless, over the next few days he embraced his physical therapy routine, treating his rehabilitation like race training. "If I did one session of five steps, I'd think, Tomorrow I'll do two. It hurt, but I was coming back from the mother of all injuries."
Seven weeks after he was admitted, Cornell went home from the hospital. He spent his days lapping the dining room table, gradually growing stronger until one day he ran a few steps. "It was very jarring. I felt awkward and off-balance." But he continued to add distance, alternating running and walking. "With the amputation, I looked pretty weird, so I was self-conscious. But I remember thinking, If this freaks people out, screw 'em."

In May 2005, seven months after his diagnosis, Cornell returned to the Bolder Boulder. Walking it with his daughter Eliza, then 8, he finished in two hours. "It was a really joyous moment," says Cornell. "I felt a great sense of being back."

The amputation has changed how Cornell runs. He leans to the left and swings his right arm away from his body as a sort of counterweight. But as he adjusted to his new anatomy, his times improved. In 2008, the 46-year-old ran the race in 53:35 and realized his long-held dream of besting his age might not be dead after all.

Since then, Achilles and knee problems have hampered his racing efforts. But he's returned to work in the lab and travels the country as a scientific ambassador. For Cornell, physics and running share a pair of key traits: "They're both hard, and they both reward focused effort." To that end, on May 30, Cornell will toe the line at Bolder Boulder for the 13th time.

Carl Wieman, who shared the Nobel Prize with Cornell, is hopeful his friend will eventually achieve his goal. "He's approaching it in an incredibly scientific fashion, monitoring his times and workouts extremely carefully," says Wieman. "It's a classic physics nerd approach."

Still, says Cornell, at least in this realm of his life, numbers don't tell the whole story. "Even if my race performance goes poorly, I always have a great time. With everything that's happened, just to be out there running is a victory."

LAST YEAR THE BOLDER BOULDER 10-K HAD 50,420 FINISHERS, MAKING IT THE SECOND LARGEST ROAD RACE IN THE UNITED STATES.