CHAMPAIGN, Ill. — On a recent afternoon, Tatyana McFadden wheeled her racing chair onto a quiet street to begin a training session. She rolled through the University of Illinois campus here, past the football stadium, by a cemetery and then a residential street lined with bungalows. Cornfields were in the distance. Her legs, which she has never used to walk, were tucked beneath her torso.

McFadden kept her head down, her back muscles rippling with each stroke of her arms. After 10 miles, her loop was finished. She was back at the education rehab center, wearing a bright smile.

“Before, 10 miles used to be so hard,” she said. “Now it’s just a recovery day.”

McFadden, a 24-year-old senior, was born with spina bifida, which left her paralyzed from the waist down. She arrived on campus as a decorated sprinter, and she has 12 medals — three gold — from the last three Paralympic Games, in Athens, Beijing and London.

Now she is one of the world’s leading long-distance wheelchair athletes, having won the Boston Marathon and the London Marathon this year. When she races in the Chicago Marathon on Sunday, she will attempt to become the first person — able-bodied or disabled — to win three major marathons in the same year.