"LEGS TIGHT ... BUTT TIGHT ... BREATHE" Video from the Air Force centrifuge at Randolph AFB

STRAP IN AND FEEL THE G's
Video shows a gradual onset ride to a maximum of 7G's in a centrifuge.
And a rapid onset ride to a maximum of 7G's.
Watch upper left hand corner for G forces
This is how they train to prevent GLOC. (Gravity-induced Loss of Consciousness)