While you're on the treadmill, your body is moving, but the world isn't shifting past you like it does when you're striding on solid ground. You end up with zero optic flow—the motion of the visual world as you move. Once you step off the machine, the universe moves with you again. With positive optic flow suddenly back, your brain vastly underestimates the speed at which your surrounding visual field should be moving, creating a feeling of acceleration, Pelah says. If blindfolded, you move forward while attempting to stay in place because your body still thinks that forward motion keeps you stationary. It takes a few minutes for things to recalibrate.