LOS ANGELES — The worst day of Aaron Baker's life wasn't when the then-20-year-old motocross racer crashed his bike one spring day in 1999, flew over the handlebars and hit the ground head-first, paralyzing him from the neck down. No, the worst day came a year later when Baker's physical therapists, marveling that he could actually stand on his own and move his arms some, cautioned him not to expect much more. The chances of walking again, he was told, were one in a million. He eventually used that as a mantra — when people say odds are a million to one, ignore the million and focus on the one — and has learned to walk again."At first it was even one in a million that I would feed myself, so walking seemed out of the question," said Baker, who recently completed a leg in the Wings For Life run to raise awareness of spinal-cord research. "So after a time we learned to focus on just the one. Our approach to the whole process became just one breath, then one movement," until small victories began to add up. Baker, 36, who now gets around with just a cane, emphasizes he didn't run far during his leg at last month's event; maybe just a quarter mile. When he left the hospital after his injury, he never imagined such accomplishments. "I was ready to drive my electric wheelchair right into the swimming pool" at the modest motel that he'd first moved to. "I mean I wanted to work hard. I wanted to overcome this thing," he said. "But there were no other options. Insurance wasn't going to cover any more at the hospital and local gyms weren't adapted to help someone like me." His mother, Laquita Conway, took him to the Center of Achievement Through Adapted Physical Activity, an institution at California State University, Northridge, known for its pioneering work in developing rehabilitation therapies. For 15 years, he went to see Taylor-Kevin Isaacs, the former CSUN professor. "When Aaron told me he thought he had a one in a million chance of walking again, I told him, 'Let's think of grabbing onto the one and forgetting about the million,' " Isaacs said, recalling their first meeting when Baker struggled just to shake hands. Isaacs put Baker on a regimen stressing nutrition, flexibility and repetitive exercise. "But the key part is human determination," said Isaacs, adding he'd never seen anyone with more than Baker. There is no magical medical cure for an injury like Baker's, in which he fractured the fourth, fifth and sixth cervical vertebrae, said Dr. Charles Liu, director of the University of Southern California's Neurorestoration Center. "He just kept working at it like crazy," said Liu. "The message is you should never give up."