Your Center Of Gravity Leaves Your Body

Stand up straight. There is a point about halfway up you that every equation of motion treats as your entire body - and it is not a place. It is an average, recomputed from wherever your limbs happen to be.

Raise your arms and it climbs. Lean and it slides. Bend far enough forward and it travels out through the front of you and hangs in open air, in a spot where there is no body at all. Standing normally it is inside you: a little above the middle, about 57% of your height in men and 55% in women, measured from the floor to the top of your head, and roughly an inch in front of the top of the second sacral vertebra. It shifts with build and posture.

Then the part that is not bookkeeping. The instant your feet leave the floor, that point is locked onto a curve and nothing you do can move it. Not your arms, not your legs, not a twist. Moving one part of you toward something moves the rest of you away by exactly as much, so only gravity gets a say. Your jump is decided before you are airborne, and everything after that is decoration.

Which is why a high jumper can arch backwards over the bar while that point passes underneath it. The body clears. The point never has to.

Sources:
https://en.wikipedia.org/wiki/Center_of_mass
https://www.physics.unlv.edu/~jeffery/astro/mechanics/center_of_mass_fosbury_flop.html
https://chiro.org/ACAPress/Body_Alignment.html