Hysterical strength, or superhuman strength, is a display of extreme strength by humans, beyond what is believed to be normal, usually occurring when people are in life and death situations. Common anecdotal examples include parents lifting vehicles to rescue their children. Such examples, however, have not been proven and have been dismissed by doctors across the world. The extra strength is believed to come from adrenaline, though incidents are rare and never proven as there were no examinable evidence or witnesses; research into the phenomenon is difficult, though it is thought that it is theoretically possible.