Six Flags Closes Its X2 Roller Coaster After Brain-Injury Lawsuits

The shearing, tearing, and torquing forces at work on extreme roller coasters affect the brain, experts say. 

“Brain tissue has very low rigidity (similar to jello), so it is prone to shearing and twisting during head motion,” wrote Lyndia Wu, an associate professor in the department of mechanical engineering at the University of British Columbia who studies the mechanics of brain injuries, in an email to TIME. “The tissue shearing and twisting can be amplified when the head rapidly accelerates or decelerates, such as when it moves in one direction and then abruptly whips in another during a roller-coaster turn, or when it strikes a headrest or another object. Blood vessels can also be experiencing stretching and twisting, posing risks of rupture and bleeding.”

The high levels of acceleration the coasters generate are a complicating factor. The head, which moves and swivels throughout a ride, may take more of a pounding than, say, the relatively stationary torso. G-force calculations, Wu says, only apply to “whole body accelerations that can be measured [or] estimated at the seat level when the roller coaster is designed. The head can be experiencing different acceleration profiles during a ride, which bring about additional brain injury risk considerations.”