jackass's johnny knoxville experienced a brain hemorrhage during filming of latest movie

in a video that no doubt had neurologists and emergency-room doctors cringing, johnny knoxville (of jackass movie franchise fame) stands dressed in a matador costume, staring down a charging bull who then launches him head over heels, spiraling into the air.

knoxville, who has had 16 concussions from the previous jackass films, explains that this stunt in the latest jackass forever films left him with a serious brain injury that makes him question if he will take part in any future movies.

“i got a brain hemorrhage from that, so my cognitive abilities were in steep decline after that hit,” knoxville said on the howard stern show last week.

a brain hemorrhage (or a “brain bleed’) occurs when blood vessels rupture inside the brain. this is a serious injury because, depending on the severity and location of the bleed, it can reduce the oxygen flow to brain cells. these cells can only last about three to four minutes without oxygen before they begin to die, so any interruption to the blood flow can be critical.

how many head injuries are too many? research isn’t sure.

concussions fall under the category of traumatic brain injury, according to the cdc, and are caused by a hit to the head or a sudden force to the body that causes the head to jerk around. a brain hemorrhage may also occur when this happens, but not always. during impact, the brain itself can slide into the hard walls of the skull, causing lasting damage that is difficult to see with common imaging techniques like mris. this is one of the reasons that concussions are so tricky to understand.

canadian estimates peg about 200,000 concussions annually, however, a study on concussion rates in ontario found that on average there are about 1,153 diagnosed concussions per 100,000 people each year (1.2 per cent of the province’s population.) there aren’t any statistics for how many head injuries also co-occur with brain hemorrhages.

recently, the u.k. rugby health project found a strong correlation between the amount of concussions experienced by a player and negative mental health outcomes. retired athletes who had five or more concussions were more likely to score higher on global anger and covert anger tests, and have a higher overall negative mental health score. an increasing body of research also points to risks of physical and psychological damage that can occur even years after concussion symptoms seem to have subsided.

while many sports organizations have begun to adopt a “three concussions, you’re out” philosophy, dr. elizabeth m. pieroth, a board certified clinical neuropsychologist and the associate director of the northshore university healthsystem sports concussion program , says this guideline is more arbitrary than based on concrete evidence.

pieroth writes in the nfl evolution blog that two concussions might be all it takes to end a sports career for some athletes, while others may not show significant side effects after multiple head injuries. instead, she says she bases recommendations on present symptoms, the length of time between concussions, personal and family medical history and psychiatric history, as well as any alcohol or illicit drug use.

research also points to the personal nature of head injuries. in a 2018 study , researchers attached accelerometers to the helmets of 319 collegiate football players with the goal of capturing “linear and rotational head accelerations.” during the course of the study, 22 of the players experienced 25 concussions (three of the players experienced two concussions each during the study period.) the researchers didn’t find a correlation between the data collected by the accelerators — linear and rotational accelerations or the location of impact on the head — with concussion symptoms experienced, the severity of symptoms or the time it took for the symptoms to subside. there also didn’t seem to be a threshold for the severity of impact that would trigger a concussion.

as for knoxville, after months of speculation if jackass forever would be his last movie, it seems to be time to put the injury-laden franchise behind him.

“after this, i can’t put myself on the line with stunts that can forever change my life,” he told stern. “…after the bull hit i’m like i think i’ve done enough. i don’t have anything to prove .”