In the jumping events, an athlete’s center of mass is predetermined at takeoff.
This is obvious (well, kinda), but it’s neat to think of it in those terms.
Any projectile follows a parabolic curve. Looking at, say, a long jumper, that curve starts at the location of the athlete’s center of mass (probably around their navel) as they fire off the board. It continues UNALTERABLE until the athlete lands in the sand. Now, what the horizontal jump can control (to some extent) is how their body rotates around that center of mass to help them gain some distance on the landing. This is why straight-legged, upright landings often seen in younger jumpers are frustrating for coaches. The athlete interrupted the flight of their center of mass! Follow the curve to see where they could/should have landed. This is why the ideal horizontal jump landing is with the toes pointed skyward. When the heels hit the sand, the goal is the anticipated landing point of the athlete’s center of mass. i.e. your butt lands right at or just after where the heels hit.