What’s the maximum speed a human can withstand?
Whilst fighter pilots are able to take more than the rest of us, the speed we travel at can be fatal.
It’s not speed that’s the problem, but acceleration or deceleration. That’s what kills in a collision, for instance. Changes in speed are expressed in multiples of gravitational acceleration, or ‘G’. Most of us can withstand up to 4-6G. Fighter pilots can manage up to about 9G for a second or two. But sustained G-forces of even 6G would be fatal.
Astronauts endure around 3G on lift-off, one G of which is Earth’s own pull. This is marginally easier to bear because the crew sit in a laying down position, so the G-force acts from the back to the front of the body rather than top to bottom, where blood would be forced down from the head.