Washington ( CNN ) -- The death of Caleb Moore is shining a spotlight on growing concerns over safety in extreme sports . The freestyle snowmobiler , attempting a backflip last week at the Winter X Games in Aspen , Colorado , could n't rotate his machine enough to land the maneuver . The skis dug into the lip of the slope , bringing the 450-pound snowmobile crashing down on him . The vehicle slammed into Moore 's head and chest . After initially diagnosing Moore , 25 , with a concussion after Thursday 's accident , doctors soon discovered bleeding around his heart . He had emergency surgery at St. Mary 's Hospital in Grand Junction on Friday , a day after the accident . He had brain complications , and his family issued a statement saying he was in critical condition and being closely monitored . On Thursday , a week after the accident , Moore died . The combination of quirky , hair-raising events that make up the X Games were once pushed to the distant margins of televised sports . But in recent years , some have been added to both Summer and Winter Olympic slates . `` They do train all year for this , '' said Dr. Christine Trankiem , a trauma surgeon at Medstar Washington Hospital Center . `` But it 's important for the folks watching at home to realize that these acts , while exciting to watch , are potentially life-threatening , limb-threatening and brain-threatening acts if an accident should occur . '' Moore 's injury was one of several at this year 's Winter X Games . His younger brother , Colten , suffered a separated pelvis in the same event . Freestyle skier Rose Battersby , a New Zealander , incurred a spinal fracture , and Icelandic snowboarder Halldor Helgason suffered a concussion . Sebastian Landry , a filmmaker who specialized in snowmobile features , told the New York Times last year that injuries in the sport made him lose interest in filming . `` It seemed like every time we went to the mountains somebody went to the hospital , '' Landry told the Times . `` Kids get stars in their eyes and just want to go for it . That , plus being raised with the motor-head mentality where it 's all or nothing . '' It 's not just the athletes who appear to be at risk . During one of the jumps on Sunday night , Australian Jack Strong was attempting a backflip on his machine when it got away from him . The runaway snowmobile crashed into a bank of fans . A young boy who hit his knee on a parked vehicle while trying to get away was evaluated and released ; other spectators avoided injury . Strong was not seriously injured . ESPN , which organizes and televises the X Games , says it is constantly working to ensure the safety of competitors . On Thursday , the network said it was deeply saddened by his death . `` As a result of this accident we will conduct a thorough review of this discipline and adopt any appropriate changes to future X Games , '' ESPN said in a statement , adding that Moore was `` a four-time X Games medalist who fell short on his rotation on a move he has landed several times previously . '' ESPN says the safety of fans is also a priority . `` We 've worked closely with athletes , risk management specialists , sport organizers and event managers to ensure the safest possible conditions for athletes and spectators alike . Further measures are constantly being evaluated to ensure the safest possible experience for spectators , '' the network said in an earlier statement . One thing spectators wo n't experience : a drop-off of the X Games . ESPN says it is expanding the Summer X Games to Munich , Germany ; Barcelona , Spain ; Foz do Iguacu , Brazil ; and Los Angeles . The Winter X Games were expanded this year to include Aspen and Tignes , France . `` This is something that is truly valuable for sponsors , for ESPN , in terms of generating tens of millions of dollars of revenue , in terms of subscriber fees and advertising sales , '' said Lee Berke , president and CEO of LHB Sports , Entertainment & Media Inc. Berke said that while ESPN did not win the U.S. rights to televise the Olympics , `` they 've gone about making the X Games their own Olympics . '' X Games kicks off with tribute to fallen champ Sarah Burke . CNN 's Josh Levs contributed to this report .
A snowmobiler is fatally injured during practice . Questions are raised over safety . ESPN says it has worked to improve athlete and spectator safety .