In Olympic high-diving, athletes leap from a maximum of 10 meters above the water. Although the force of their water impact is substantial, it’s small enough that they can enter the water head first. For cliff divers — who may jump from 27 meters! — the impact force is too great to risk a head-first entry, so they enter the water feet first. But this does not eliminate their risk of injury.
As the diver’s body enters the water, each leg creates its own cavity, and the proximity of the two cavities generates a repulsive force. If the diver isn’t prepared to resist that force, it will force their legs apart, potentially injuring them. (Image and research credit: T. Guillet et al.)