ASPEN - The image was chilling: Snowmobile rider Caleb Moore, launched over his handlebars on a backflip gone wrong, rolled down the landing hill with his 450-pound machine somersaulting behind him.
Run over by his sled, Moore lay on the snow for several minutes before being helped off the course. As of Wednesday, he was hospitalized in critical condition because of bleeding around his heart and a complication involving his brain.
Moore's was the worst accident at the Winter X Games, which wrapped up Sunday night after four days of competition, but it wasn't the only harrowing moment. The wipeouts included a runaway snowmobile that sent spectators scrambling.
Even the highlights were hardly tame. Snowboarding star Shaun White soared a competition record 24 feet into the air during the superpipe competition, and fellow boarder Elena Hight showed off a difficult trick called a "double alley-oop backside rodeo" that involved a couple of backflips and a 180-degree rotation. It had never been seen in a competition.
All that, plus Moore's crash, has some wondering whether dialing up the difficulty each year improves action sports or has simply made them too dangerous.
"Should we be asking these questions? We absolutely should be," said Dan Lebowitz, the executive director of Sport in Society at Northeastern University, which examines the role of sports to promote healthy development and social responsibility.
The people performing these superhuman feats "really are just human," he said. "How do we maintain safety in that progression when that progression sometimes pushes every envelope to some amazingly extreme point?"
Moore's injuries underscore the dangers at Winter X, which was filled with numerous cover-your-eyes crashes.
Halldor Helgason of Iceland over-rotated on a flip in the snowboard big air competition and had to be taken off on a sled with a concussion. Rose Battersby of New Zealand sustained a lumbar spine fracture in a wipeout during practice before the skiing slopestyle competition, which will be an Olympic sport next winter at the Sochi Games.
Then there was this: Summer X Games motocross champion turned snowmobile newcomer Jackson Strong tumbled off his machine during the best trick competition, the throttle sticking and the sled swerving toward fans as they scurried away. The machine came to a rest when it got tangled in some netting and no one was seriously hurt.
Such a scenario had already crossed the mind of Levi LaVallee, a snowmobiler who captured two gold medals only to be sidelined for the final two competitions after tearing a muscle in his back.
"I've always thought about, 'What happens if the thing tips over and the throttle sticks?'" LaVallee said. "It was good, though, because it showed that X Games has a good setup with the fencing."
Whether action sports are too dangerous is an issue that's been raised before.
When freestyle skier Sarah Burke died in a training accident a little more than a year ago in Park City, Utah, there were questions about the halfpipe. Before that, the sport was examined when snowboarder Kevin Pearce suffered a severe brain injury in a fall in the same pipe as Burke two years earlier. Pearce has recovered and served as an analyst at Winter X.
But in general, the athletes accept the risks and defend their disciplines.
"To lose Sarah was such a blow to this entire industry," said snowboarder Gretchen Bleiler, who didn't compete this year as she recovers from a serious eye injury she suffered in training. "This sport brings so much joy, happiness and balance to my life and that far outweighs what could happen. You can't ever live your life with what could happen."
In a statement, X Games officials said they've paid close attention to safety issues over the event's 18-year history: "We've worked closely with athletes, risk management specialists, sport organizers and event managers to present the best possible experience for athletes and spectators. Further measures are constantly being evaluated."
Athletes say they prepare as best they can by trying out new tricks into foam pits and air bags set up at the bottom of courses. But even all the caution in the world can't prevent the fact that sometimes well-practiced maneuvers can go wrong in the air.
"You don't want to live your life in fear because of a situation," LaVallee said. "Look, I'm driving down the road right now and the worst-case scenario is a car could swerve over into my lane and run over me - there it is, end of the road.
"That's kind of the same thing we think when we're competing. Hopefully, the preparation and countless hours of training and practicing will prevent the worst-case scenario from happening."
Tucker Hibbert - the Shaun White of snowmobiling after winning his sixth straight SnoCross title - just hopes casual fans understand that what they see on television is not true snowmobiling.
"You're seeing the most extreme side of what we do," Hibbert said. "That's a lot different than what the average person does on a snowmobile."
Hibbert doesn't participate in events such as best trick because, "I just wasn't born with those skills. I sit back and watch those guys, enjoy what they do."
"You just hate to see anyone crash, anyone get hurt," Hibbert said.
Moore was in the middle of an impressive run in the freestyle event when he caught the top of the hill that was serving as a landing area. He initially walked away with help and went to a hospital with a concussion.
Moore later developed bleeding around his heart and had surgery. His family said that Moore, of Krum, Texas, also had a complication involving his brain.
Colten Moore, Caleb's younger brother and defending champion in the event, separated his pelvis in a crash later that same night.
LaVallee is no stranger to horrific wipeouts.
While training for the "Red Bull: New Year. No Limits" daredevil series two years ago in Southern California, LaVallee lost control of his snowmobile high in the air and landed violently on his side, bouncing down the landing ramp. He broke ribs, cracked his pelvis, collapsed one lung and punctured the other.
But he returned the next year and jumped a record 412 feet, 6 inches.
"We're passionate about the sport that we're in," LaVallee said.
"Anyone who competes has that drive to succeed, to go bigger than the next person or be the first one to do it."
The mentality is similar throughout action sports, even if the bar keeps getting raised.
"There are going to be benchmarks set and people trying to exceed that benchmark," Lebowitz said. "That's just the essence of our society and our social culture."