The BMX racecourse at Olympic Park is part asphalt, part dirt and all danger.

When the competition concluded on a hot Friday afternoon, three men and three women stood atop the podium to accept medals. The rest of the BMX field could barely stand at all, their mettle tested and many cases conquered by one of the most unique — and perilous — sports in the Olympics.

BMX racing graduated from after-school activity to the X-Games and then four years ago to the Summer Games in Beijing. It stands as the only action sport on the Olympic menu. The thrills and spills are usually reserved for the Winter Olympics, but this week's BMX competition featured plenty of both.

“Because it’s the Olympics everyone was riding over their heads, going for stuff they wouldn’t normally go for,” said American Connor Fields, who went down in the final race Friday and finished seventh here, four spots away from a medal.

There were more than 20 crashes in Thursday’s runs, and crashes marred four of the first six races. They played a big role in Friday’s semifinals, as well.

In one race Thursday, a French rider collided with American David Herman entering the first turn and together they wiped out nearly the entire field. New Zealand’s Marc Willers cruised to victory, as he was the only rider still on his bike.

The first men’s run Friday wiped out all but the top three finishers. The scariest moment, though, came during one of the women’s semifinal runs. After crashing on the course’s first straightaway, Brazil’s Squel Stein had to be taken off the course on a stretcher. She was reportedly able to move her limbs but was undergoing medical tests Friday evening.

The Olympic event measures about a quarter-mile, beginning atop a ramp more than 25 feet above the course. Riders can reach speeds of up to 35 mph as they attack a series of bumps and turns, hoping to stay on two wheels before reaching the finish line.

“This is a sport where you fall down and get up again,” said Colombia’s Carlos Mario Oquendo Zabala, who crashed twice in the early races and still won bronze in the finals.

Sometimes it takes longer to get up. Those who do stand a good chance of a medal. Though the sport was born on the dirt tracks of California, no American riders reached the medal podium in London. The United States won three of the six BMX medals in Beijing. On Friday, Colombia's Mariana Pajon won the women's race, and Latvia’s Maris Strombergs took gold in the men's.

The experienced riders say crashes are inevitable in BMX racing. Everyone’s going down at some point and injuries are going to happen. The top riders in Friday’s runs had an impressive collection of healed collarbones, repaired knees and just about every broken bone possible.

Brooke Crain was the lone U.S. women to qualify for the finals, and she did it just two days after tearing a quardriceps muscle on the course. Still, she was back on her back Thursday and Friday. “It was a lot to push down the hill,” she said.

Crain, who finished in eighth place in the final, was originally an alternate on the American team and was only in London because another U.S. rider suffered serious injuries last week. Arielle Martin had qualified for the Summer Games, but during her last training run July 30, her bike chain broke. Martin crashed, suffering a lacerated liver and collapsed lung that required three surgeries.

“I’m here to represent her,” Crain said. “I was just the alternate, so I’m riding for her.”

All the riders have their war stories and battle wounds, yet they keep getting back on the bike. Last July, Alise Post blew out her knee on a bad 35-foot jump. She couldn’t ride for six months. On Friday, she crashed in two of the three semifinal runs. The second came on the final straightaway, and Post struggled to get on her feet. She had to be helped off the course.

“Honestly, I couldn’t tell you what happened,” she said later. “It’s really a blur. . . . I’m just glad, I guess, that I’m physically okay.”

The 21-year-old says she hopes for a better performance at the 2016 Olympics.