Jan. 29, 2013 -- intro: Adrenaline junkies who live to catch big air or shred a race course at top speeds have fueled a booming competitive community that wants to push the human body to the extreme.
Extreme sport competitions such as the X Games and Core Tour were born out of athletes who live and breathe doing flips on snowmobiles, landing 1,080-degree turns on skis and BASE-jumping off 2,000-foot cliffs.
But even the best daredevils have suffered unimaginable injuries, some fatal, doing what they love.
quicklist: 1 category: title: Caleb Moore, Snowmobiler url: media:18339106 text: Texas snowmobiler Caleb Moore remains in critical condition days after his snowmobile flipped on top of him in a violent crash during competition at the Winter X Games in Aspen, Colo.
The 25-year-old medal-winning athlete from Krum, Texas, developed complications in his heart and brain after suffering an accident last week during the Snowmobile Freestyle finals. Moore was completing a backflip when he came up short and the skis on his sled slammed into the landing, causing the 450-pound machine to flip end-over-end on top of him.
An online fundraiser has been set up on behalf of the Moore family. For more information, visit the website.
quicklist: 2 category: title: Jeb Corliss, BASE Jumper url: media:15382306 text: Famed BASE-Jumper Jeb Corliss suffered devastating injuries after he smashed into some rocks at 120 miles-per-hour during a jump Jan. 16, 2012, in South Africa.
Corliss, 36, who made a name for himself making more than 1,000 jumps, including from landmarks such as the Eiffel Tower and the Golden Gate Bridge, said he was convinced that this was the jump that had killed him.
"One part of my brain was just going through this concept of fly, fly, fly, fly, keep going, keep going, and then the other part of my brain was like going, well, why even pull at all, basically you're dead, dude," Corliss told ABC News' Dan Harris in February 2012, in an exclusive phone interview from the South African hospital room where he was recuperating from the crash.
Despite his severe injuries, Corliss said he will continue jumping for the rest of his life.
"That's what I live for," Corliss told Harris. "The only reason I'm getting better is so that I can jump again," he said. "That's what I do. There's absolutely nothing in this world that's going to stop me from jumping."
quicklist: 3 category: title: Sarah Burke, Freestyle Skier url: media:15341076 text: Canadian freestyle skier Sarah Burke, a gold-medal hopeful for the 2014 Winter Olympics, died on Jan. 19, 2011, after sustaining a traumatic brain injury in an accident on a half-pipe course in Utah.
The 29-year-old Winter X Games champion and 2005 half-pipe world gold medalist suffered "severe irreversible damage to her brain due to lack of oxygen and blood after cardiac arrest," according to a statement from Burke's publicist.
Freestyle skiing is something of a daredevil sport, a sort of trick skiing that uses the half-pipe, which is normally used by snowboarders. Burke, who was described as a "pioneer in the sport," was training for the 2012 Winter X Games in Aspen, Colo., when she was injured.
Burke's accident occurred on the same course where snowboarder and Olympic medalist Kevin Pearce suffered a traumatic brain injury in 2009.
quicklist: 4 category: title: Kevin Pearce, Snowboarder url: media:15165745 text: It took Olympic snowboarder Kevin Pearce years to get back on his board after suffering a traumatic brain injury while on a halfpipe run in Utah.
In 2009, the now 25-year-old from Hanover, N.H., fell into a coma after slamming his head while practicing a complex stunt, and it seemed doubtful he would ever return to the sport he mastered; doctors weren't even sure he would ever walk again.
But Pearce battled through two years of intensive rehabilitation and regained his ability to not only talk, walk and eat but to get back on the slopes.
"I can't even explain what I've been through, to really get away and get on snow is just so special and I never knew it would be like that. When I was doing it two years ago, I took it all for granted," Pearce told the Denver Post in December 2011.
quicklist: 5 category: title: Mat 'The Condor' Hoffman, BMX Rider url: media:15776295 text: BMX legend Mat Hoffman, nicknamed The Condor, has had 22 surgeries to repair his broken body after sustaining severe injuries during stunts and competitions.
Considered to be one of the best vert-ramp riders in the history of the sport, Hoffman's worst injury occured in 1993, when he said he "technically died." While riding his weedeater motorbike on a 21-foot half-pipe ramp he built himself, Hoffman said he cleared 22 feet of air off the ramp, crash-landed and ruptured his spleen.
"I lay down, and while waiting for the ambulance I started to feel thirsty. I stood to get a drink, but my heart stopped and I fell against a wall and passed out," Hoffman told ESPN in a 2007 interview.
The now 41-year-old rider went to Canada to have an artifical ACL implanted in his knee.
Aside from winning multiple gold metals at X Games and BASE-jumping his bike off Norwegian cliffs, Hoffman also launched a successful production house, Hoffman Promotions, and brand of BMX bikes, Hoffman Bikes.
quicklist: 6 category: title: Stephen Murray, BMX Dirt Rider url: media: 15776329 text: BMX dirt rider Stephen Murray, 33, suffered a career-ending injury after enduring an incident that has been called one of the worst crashes seen in the BMX sport.
Murray was competing at the BMX Dirt Finals at the Dew Tour, hosted in Baltimore in June 2007, when he went to complete a back-flip on one of the last set of jumps. He couldn't rotate the bike in time and crash-landed on his head, breaking his neck. He stopped breathing but was revived on site and was rushed to the hospital.
The BMX Dirt gold medalist from Newcastle, England, suffered severe damage to his spinal cord, and despite undergoing several surgeries to repair his crushed vertebrae, he was paralyzed from the shoulders down.
"Dealing with a spinal cord injury, it's cruel, torture, you have to be removed from it, there are no easy days, every day is hard," Murray said in a 2009 interview in Ride UK BMX Magazine.
His injuries and others have since helped spawn the Athlete Recovery Fund, which collects donations to help cover medical expenses for athletes.
quicklist: 7 category: title: John Kucera, Downhill Ski Champion url: media: 15776244 text: John Kucera, one of the world's leading downhill ski champions, can only seem to catch breaks -- in his leg.
In 2009, the now 28-year-old Canadian suffered a broken leg when he crashed during the World Cup super-G race in Alta, Canada, killing all hopes for any 2010 Winter Olympic showing.
Then, on Feb. 16, 2012, Kucera told Canadian news outlet, CBCSports, that he re-injured the leg in a crash while skiing ahead of the men's U.S nationals downhill race in Aspen, Colo.
"I'm kind of shocked," Kucera told CBCSports at the time. "It's a bad luck situation. My ski just popped off... The injury is not nearly as severe as last time. I'm going to stay focused on coming back as soon as I can."
quicklist: 8 category: title: Bethany Hamilton, Surf Champ url: media: 15776064 text: Professional surf champion Bethany Hamilton nearly died after a shark attacked her arm while she was surfing off the coast of Hawaii almost eight years ago.
She was just 13 years old at the time.
"I was lying on my board sideways. And then ... the shark came up and grabbed ahold of my arm," Hamilton told "20/20" in a November 2003 interview.
"And then, I was holding on to my board, with my thumb, because I probably didn't want to get pulled under. It was like pulling me back and forth, not like pulling me underwater. Just like, you know how you eat a piece of steak? It was kind of like that. And then it let go. And then went under. Then I looked down at the water, and it was like really red, from all the blood in the water."
Many worried this rising star's career was over, but Hamilton was back in the water a month after the attack to re-teach herself how to surf. The now 22-year-old Kauai, Hawaii, native told ABC News in a March 2011 interview that while she was blown away by what happened to her since losing her arm, it gave her new perspective.
"I definitely would allow the shark attack to happen," Hamilton said. "The thing for me is, I know that God allowed it to happen because of all the good stuff that has come from this terrible experience."
Hamilton worte a book about her life, "Soul Surfer: A True Story of Faith, Family and Fighting to Get Back on Board," in 2004, which was adapted into a Hollywood film, "Soul Surfer."
quicklist: 9 category: title: Jeremy Lusk, Freestyle Moto X Star url: media: 15776187 text: Jeremy "Pitbull" Lusk, an X Games gold medal winner known for his freestyle motocross stunts, died from severe head trauma during a crash at a competition in 2009.
He was 24.
The California native was competing at an FMX contest in San Jose, Costa Rica, and attempted a back-flip variation during a 100-foot jump. But when he failed to fully rotate the bike around and struggled to get back into the bike's seat, Lusk slammed head-first into the dirt on a landing ramp's down-slope.
At the time, a spokesman at the Calderon Guardia Hospital in San Jose told the press he had suffered severe brain damage and a possible spinal cord injury.
In the wake of his death, the Jeremy Lusk Trust Fund was set up within the Athlete Recovery Fund. Donations can be made through their website: athleterecoveryfund.com.