Today's high jump technique: you cross the bar on your back while your centre of mass can pass underneath it. Dick Fosbury took Olympic gold with it in 1968.
The flop looks absurd and is pure physics: the arch lets your centre of mass travel under the bar while your body goes over it. How superior it is shows in how fast it spread — four years after Fosbury's 1968 Olympic win, 28 of 40 finalists were using it, and its predecessor the straddle, crossing belly-down, is now history. The costliest fault is rotating too early: lean towards the bar at take-off and you simply lose height. Rotation starts only after you leave the ground — head first, shoulders following — and the arch forms once your hips reach bar height. The most dangerous fault is its mirror image: too much backward rotation is the main reason people land on the neck or high on the shoulders instead of flat on the upper back. A diagnostic: where the bar falls names the cause. Hips means the arch; legs means you pulled the lower legs up too slowly.