Though most injuries involve bumps, bruises, broken bones and concussions, fatalities do occasionally occur. Injuries plagued much of his career, including MCL sprains, ACL sprains, and concussions. The most common types of injuries are strains, sprains, bruises, fractures, dislocations, and concussions. American football players are prone to head injuries such as concussions. CTE is caused by repeated concussions and subconcussive head injuries. Biycling is a sport in which participants are at risk of concussions and head injuries. He is largely able to withstand corrosives, punctures and concussions without sustaining injury. Rarely, massive hailstones have been known to cause concussions or fatal head trauma. After retirement, Portis admitted to have suffered 10 concussions. Female athletes are also more prone to concussions than male athletes. The symptoms of most concussions resolve within weeks, but problems may persist. Danzig stated he retired due to concussions and accumulated brain damage. He was only officially diagnosed with a few concussions. Daniel Bryan was also forced to retire due to severe concussions. He says that he hopes that his work will help to prevent concussions in football.