Wheelchair racers Hannah McFadden, left, and sister Tatyana McFadden train together at a high school in Clarksville, Md., on Aug. 21. (Linda Davidson/The Washington Post)

Tatyana McFadden whips around a track near her home in Clarksville, Md., hunched over, focusing on the next move, the next push. Her arms spin in long, ordered strokes, propelling her racing wheelchair.

Her younger sister, Hannah, follows close behind, her arms hitting shorter, higher strokes on her wheelchair as the two spin like dueling comets.

“On that track . . . they are competitors,” Deborah McFadden says from the sideline as her daughters, both Paralympians, fly by.

These are heady days for the McFadden sisters. Tatyana, a soft-spoken 24-year-old with colossal shoulders and an implacable drive to win, has earned a dizzying number of superlatives and victories, including at the this year’s Boston and London marathons less than a week apart. She’ll be racing in the Chicago Marathon on Oct. 13.

Born in Russia with spina bifida and adopted by her American mom, she’s been fighting ever since — first for the right to race, and now to win.

Her sister, Hannah, 17, adopted in Albania, was born with a congenital bone disease that led doctors to amputate her left leg above the knee. She competes at Tatyana’s alma mater, Atholton High School, a public school in Howard County.

Hannah is just breaking into the top ranks of wheelchair racers in the United States, having already competed at the 2012 Paralympic Games. But she will have to catch her sister to get to the top of the sport.

Doctors in Russia didn’t even believe Tatyana would survive her birth, according to her mother. The spina bifida left her paralyzed from the waist down. Doctors at her orphanage in St. Petersburg waited three weeks before they operated on her to close the hole in her spine.

“It’s a miracle she didn’t die from the infection,” McFadden said.

McFadden, then a commissioner of disabilities for the U.S. Department of Health and Human Services, had traveled to Russia after the fall of the Soviet Union, tasked with delivering humanitarian aid.

When McFadden met Tatyana, the 5-year-old had already taught herself to walk on her hands. McFadden had seen thousands of children through her work, she said, but Tatyana was something special.

“I couldn’t get her out of my mind,” McFadden said, laughing, remembering Tatyana crawling into her lap and playing with her camera.

McFadden adopted her and brought her to the United States when she was 6, then began entering Tatyana in sports programs to help her become healthier and more independent. Among Tatyana’s sports were basketball, tennis, sitting volleyball, swimming, archery, ice hockey and downhill skiing.

But it was wheelchair racing that she fell in love with.

“I love, love, love, love, love to race. . . . It’s so much fun,” Tatyana said in an interview. “I wouldn’t give it up for anything in the world.”

That set the stage for Tatyana’s fight for the right to compete.

Tatyana’s quest for inclusion on Atholton High School’s track team is familiar lore to followers of wheelchair racing. After joining the team, McFadden wasn’t allowed to compete with the team’s able-bodied runners. Some argued that having wheelchair athletes racing against able-bodied runners raised safety issues.

McFadden filed two lawsuits. In the first, she sought to be allowed to compete with able-bodied runners at the same time on the same track, and the second one sought to have her results count toward team totals. The lawsuits resulted in Maryland’s Fitness and Athletic Equity Act for Students With Disabilities, which mandated that schools include disabled students in their athletics activities and allow them to compete against able-bodied athletes.

The possibility of her sister being in a similar situation was another motivation, Tatyana said. “I didn’t want her in the same position as me,” she said.

How times change, Deborah McFadden said: Hannah now races with the Atholton High team.

“They want to have me on the team,” said Hannah. “It’s an entirely different atmosphere.”

Hannah’s sister is quite a role model.

She is dominating the sport at a time when it has seen tremendous change and is far more competitive than it used to be, said Chantal Petitclerc, a renowned Canadian Paralympian who set one of the records that McFadden broke in the 2013 Paralympic World Championships in Lyons.

“She has everything she needs to make history in this sport,” she said.

The sport barely resembles the one in which Petitclerc started competing 25 years ago.

Racers needed to be dedicated, but not totally committed the way they need to be now, she said.

That changed after the Paralympic Games “took off” in 2000, she said. “Suddenly, it became a lot more serious,” she said. “It required a lot more work.”

Adam Bleakney, Tatyana’s coach at the University of Illinois, said McFadden has an “inherent gift” for sprinting and accelerating. That, combined with the thousands of hours she has trained and her competitive drive, has made her a formidable racer, he said.

“When [Tatyana] gets on the line, she’s like a greyhound; she will jump off the line,” he said.

Marty Morse, a wheelchair racing veteran who was Bleakney’s predecessor at Illinois, said that some of McFadden’s strength comes from having to learn to move around on her hands as a baby.

“Tatyana, probably as a baby, crawling around, using her arms, she just developed a bone density in her upper body that’s off the scale. . . . The triceps strength on someone like that, . . . you can train in a gym all you want and you’ll never get there,” Morse said.

McFadden’s background as a sprinter is another asset, Morse and Bleakney said.

“Being blessed with the makeup of a power athlete, being able to generate a lot of force over a short time is hugely beneficial,” Bleakney said.

After Tatyana began racing long-distance competitions as well, her sprinting background was an unusual asset. Few racers take on such a wide range of events or dominate them so completely. At the championships in Lyons, she won every event from the 100 meters to the 5,000 meters, taking six gold medals in all.

“In many ways, wheelchair racing is more like cycling, where a top tour cyclist still has to be able to sprint and generate enormous power over a short period of time,” Bleakney said.

She may be good enough to be earn her living racing, Morse said. “She is such a wonderful ambassador for the sport. . . . I see her as our spokesperson for a whole future generation, for persons with disabilities trying to get involved in sport,” he said.

“That is my dream,” McFadden said. “I want to educate others, inspire others — [to show] there are no other limitations in life. . . . I want to leave that behind.”

If she wins the Chicago Marathon on Oct. 13, she would need only a victory in the New York Marathon on Nov. 3 to achieve what her supporters are calling a “Grand Slam” — four major world marathon victories in a single year. Although other wheelchair racers have won as many marathons in a year, no one has won four of the majors.

It won’t be easy. McFadden will face winners of past marathons and other world champions. And the depth of the competition at the two marathons has improved dramatically over the years, officials say.

“We probably have the best women’s field we’ve ever had,” said Bob Laufer, the coordinator of the wheelchair race division of the ING New York Marathon.

Asked in a recent interview whether she had an arch-rival, McFadden pondered the question, laughed and replied: “Everybody!”

St. John Barned-Smith is a reporter for the Gazette.