Chest Penetration

Replaced. Chest penetration is the athlete driving the chest forward after takeoff, delaying the rotation. It is often achieved by forcefully moving the bottom arm above the head.

It was justified on two grounds. First, that it creates an elastic stretch of the muscles initiating the takeoff leg whip. Second, that by delaying rotation it keeps the center of gravity lower for longer, allowing deeper penetration of the vaulter-pole system toward vertical.

The first does little. A proper takeoff already stretches those muscles, so the additional stretch adds an insignificant whip advantage at best.

The second objective is correct, and the model shares it. Keeping the center of gravity lower for longer is worth doing.

Whichever justification is offered, the cost is the same. Chest penetration does not add energy to the system. It changes the timing inside it. The delay is a period in which no energy enters — a passive phase — inside an interval that runs between roughly 1.10 and 1.55 seconds from leaving the ground to releasing the pole, and time spent delaying cannot be recovered later in the vault.

The bottom arm is also the arm that leads rotation acceleration. Moved above the head, it is not available to do so.

What the model uses instead. The same objective, reached by a longer and more aggressive rotation of the body lever. A long lever keeps the center of gravity lower for longer on its own, and it does so while energy is entering the system rather than while it is not.