Nathaniel Brooks / The New York TimesSam Peterman, 15, a runner for Sweet Home High School in New York, falls into the arms of her father, Dale, after a state title race in Albany, New York, on Saturday. Peterman, who has neurocardiogenic syncope, an irregularity of the nervous system that causes her to faint after running, falls into her father’s arms almost every time she crosses the finish line — but she still often crosses it ahead of everyone else.

Dale Peterman watched and waited. It was all he could do.

His daughter, Sam Peterman, a sophomore at Sweet Home High School near Buffalo, New York, was 100 meters away from finishing the 1,500-meter race in the New York high school state championships at the University at Albany on Saturday. Dale Peterman stood at the finish line.

As Sam sprinted down the last straightaway, she was losing her balance — arms flailing, head cocked back, mouth agape. Her father positioned himself inches behind the line. He knew what was coming.

When Sam crossed the line, she collapsed into her father’s arms. He carried her to the infield grass and laid her down.

“I can’t breathe!” she shouted as a small team of people elevated her legs and offered her bottled water. Dale Peterman told her to calm down, told her it was over.

“Am I getting a medal?” Sam asked between breaths.

“Yes, you’re getting a medal,” her father said. “You went for it.”

Sam, of Springville, New York, finished sixth overall in the state, her time of four minutes and 30 seconds beating her previous best by almost nine seconds and nearly breaking a school record.

But the elder Peterman was relieved simply that she had finished.

Sam, 15, has neurocardiogenic syncope, or NCS, a condition that causes her to faint nearly every time she finishes a race. Dale Peterman has almost always been there to catch her.

“It’s the hardest thing,” he said of waiting for Sam at the finish line. “Because you never know.”

Brian Lombardo, Sweet Home’s coach, said: “She’s not only fighting to run fast; she’s fighting to stay on her feet. Who wants to see that happen to their son or daughter?”

Dr. Blair Grubb, a professor at the University of Toledo who has studied syncope extensively, characterized NCS in a 2005 article in The New England Journal of Medicine as the autonomic nervous system’s failure to keep blood pressure high enough to maintain consciousness.

Physical activity, he said, pools blood in the lower half of the body, reducing blood flow to the heart. In response, the heart pumps more vigorously. In people with NCS, the brain misreads that as high blood pressure and tries to lower the pressure, which leads to decreased blood flow to the brain and, thus, fainting.

“Anybody, if you push them hard enough, long enough, will do this,” Grubb said in an interview. “But there’s some people where their systems are predisposed to it.”

Sam is one of them. The first time she fainted, she was in the eighth grade, at the end of a 3,000-meter race. She was confused and scared.

It continued into high school. The worst instance, her father said, occurred last fall, when she fell a quarter of a mile from the finish of the state cross-country final and was out for 40 minutes. Her parents took her to the hospital. Sam was not allowed to run for weeks.

After Sam visited at least three doctors and wore a heart monitor for 35 days, revealing no troubling activity, her parents were relieved to learn that the fainting was not caused by a problem with her heart. Sam was cleared to run again.

In January, Sam’s father took her to Dr. Donald Switzer, a cardiologist in Buffalo. Switzer administered a tilt table test, strapping Sam to a board and rocking it back and forth to simulate changes in position while monitoring her heart rate and blood pressure. The test usually lasts 45 minutes; Sam passed out in less than three. Switzer diagnosed NCS.

Still, all of the doctors they visited, Dale Peterman said, cleared Sam to run.

“If we didn’t have the utmost medical clearance for her to run,” he said, “she wouldn’t be running.”

Grubb said the biggest danger from fainting was in hitting the ground. That is why, since the day she received the diagnosis, Sam’s father has waited at the finish line at nearly all her races.

“If he’s not there,” Sam said, laughing, “the track hurts a lot.”

At practice, when the elder Peterman is not there, Lombardo, the coach, catches Sam. He also notifies other coaches, teams and race directors of Sam’s condition.

After races, Dale Peterman has mastered the routine: Lay Sam down and elevate her legs to return blood flow to normal and help her regain consciousness. Sam said she did not usually remember the ends of races; last week, running an 800-meter race, she blacked out for the final 60 meters.

She tries not to think about collapsing at the end. Instead, she tells herself to drive her knees and focus on her form, which breaks down as the dizziness takes hold: Her right arm juts out, and her head tilts back.

The biggest question Dale Peterman still has is why she does not pass out until she finishes the race. The doctors do not know, he said. He said he thought that it was intrinsic, that her desire powered her.

Sam, whose Twitter page reads, “Everybody falls, but we get back up because the ground is no place for a champion,” won the sectional title in both the 800 meters and the 1,500 meters this season.

But she does not run because she wants attention, Lombardo said. She runs because she loves it, and because she has the opportunity to raise awareness of NCS, which accounts for 3.5 percent of emergency room visits in the United States every year, according to Grubb’s article.

Sam, who loves to go turkey hunting and to play with children, who is quiet and unassuming and smiles frequently, wants to go to college to run and become a doctor to study NCS. She uses the condition not as an excuse but as an impetus.

“A lot of people will walk away,” Dale Peterman said. “She chose not to walk away.”

It was because of that decision that on a sunny Saturday in Albany, he was nervously awaiting Sam’s race.

“I’m starting to get that uneasy feeling in my stomach,” he said, 17 minutes before the race was scheduled to start. He grew quiet.

Two minutes before race time, he pulled on a bright orange T-shirt, which matched the orange hat he was already wearing. They made it easier for Sam to find him at the finish line.

During the first laps of the race, he paced back and forth, shouting things like, “Go now!” and, “You’ve got to work!” His arms remained crossed almost the entire time.

Until the finish, of course, when Dale Peterman caught Sam and placed her in the grass to recover. He quizzed her: “How old are you? Where do you live? What’s today?”

A few minutes later, just before Sam received her medal, her father approached her for a hug. They smiled.

This time, he fell into her arms.