New football helmets come with built-in accelerometers to detect the severity of collisions on the football field. You can play spot-the-physics-misconceptions in this summary article, where the author uses acceleration, force and “g force” (whatever that is) interchangeably. The risk of concussion must depend on the acceleration of the player’s head (since that’s what causes his brain to strike the inside of his skull); I imagine the force matters if you’re worried about the player getting a skull fracture.
Apparently the threshold for concussion is about 100 g over the short term. The human body can withstand much smaller sustained accelerations, however. A few minutes at several g can cause a blackout, though both direction and magnitude matter:
- acceleration perpendicular to the spine is relatively well tolerated.
- acceleration towards the head causes blood to pool in the lower body, resulting in blackout.
- acceleration towards the feet causes overpressure in the brain, leading to a cerebral hemorrhage. Bad.
No one has managed to sneak human experiments past an institutional review board, but if we extrapolate from the great chicken centrifuge experiments of the 1970s, humans should be able to cope with – and perhaps even thrive under – modest excess gs indefinitely.