The incident was caught on video by someone in the crowd and was uploaded to YouTube. The sudden collision caused Kemper to lose control of his bicycle, skid on the track, and land on his left elbow.
Kemper had endured injuries in the past, including sports hernias, hip fractures, and a broken collarbone, his wife said, but nothing had been as bad as this.
Val Kemper said that doctors at a nearby hospital in Myrtle Beach told him to fly home to have his elbow checked out; they did not notice Kemper's open fracture. It wasn't until he saw his orthopedic surgeon in Denver, that anyone realized just how serious his fall had been.
"He had to go into emergency surgery [in Denver] just to get the wound washed out to prevent any kind of infection because it had been exposed for more than 24 hours at that time," Val Kemper said. "That was the start of a whole series of operations."
Kemper had to wait a week until his wound was clean for doctors to operate. Tom Kemper said his son had 13 screws and a plate put in to repair it, requiring him to go into physical therapy to work up his range of motion.
But at Christmastime, Kemper faced another setback. He contracted a staph infection, and underwent three surgeries in three consecutive days just to get his elbow flushed out, his wife said.
The Myrtle Beach race was more of a practice run less than a week before the October 2011 Pan Am Games in Guadalajara, Mexico. But Kemper's injury kept him out of training until February. After breaking his elbow, Kemper did not know if he would be able to qualify for the 2012 Games, his wife said.
"I think it was completely discouraging," Val Kemper said. "He didn't know if he was going to be able to get back."
Cliff English, Kemper's coach, said Kemper's injury was a major setback, but within four months, he had been given the go-ahead to resume training.
"He's very strong mentally, he's very positive, he has strong faith, and a great family. All of those things contribute to help you come back," English said. "I would say very few people would be able to come back so quickly."
Kemper had just a short amount of time to train before his last opportunity to qualify for the Olympics, at the ITU World Triathlon in San Diego, Calif. in May, English said.
"When it came to San Diego, there was no luxury of practice races," English said. "And [qualifying] was definitely by no means guaranteed."
Only two athletes at the San Diego race could qualify to represent the U.S. at the Olympics. Kemper needed to be the top U.S. triathlete in the race or finish in the top nine in order to travel to London.
But English said at the San Diego race, "you could tell [Kemper] had an aura of confidence coming off of him."
Kemper ultimately finished fifth, and secured his spot on Team USA in the London Games.
"It was definitely a challenging time, but Hunter -- he's always amazed me," Val Kemper said.
Kemper is only one of three athletes in the world making a fourth appearance at the Olympics, his wife said.
On Kemper's Facebook, he said his top goal was winning an Olympic medal. His coach said this year Kemper is looking to bring one home from the London Games.
"That thing you gotta look for is that he lives for that one day in four years," English said.
Kemper will be 40 in 2016, but both his family and his coach say that they anticipate him making an appearance at the next Olympics in Rio de Janeiro, Brazil.
"He's one of the most talented athletes I've ever worked with," English said. "He's one in a million."