How does rolling in parkour videos help them feel no pain at all? How does it not break their knee or ankle?



How does rolling in parkour videos help them feel no pain at all? How does it not break their knee or ankle?

In: Physics

It’s transferring the force away from the ground. Think of it like a river turning. If there was nowhere for the water to go it’d crash into wherever and flood but by creating a path the river can keep flowing.

Imagine two rods. One is made of solid wood and other is soft rubber. Now place them on a scale and hit their top with a hammer. Wooden scale will register higher force and the rod might splinter and break. Rubber fill disform slightly before regaining original shape and scale will have lower number.

Now imagine parkours feet like these rods. If you land with your legs straight you will break them. If you let them bend, they will act like rubber and your safe.

Now rolling allows to “bend” more but it also allows you to maintain forward energy meaning you have to dissipate less energy. Talented parkours can change downward energy to forward energy meaning they can survive very high jumps. Trick is to limit energy that goes into actual bones.

The answer is that it is just physics at work.

When you jump from a building, you gain a certain amount of energy from the fall. When you drop an item (or yourself) from a building and just let it land, all that energy gets transferred to the object, which may cause it to break.

The trick is to find a way to dissapate that energy without having to absord it all, or find a way to absorb it in a way that is more spread out.

The worst case scenario would be to land on one foot, which as you state, would probably break your ankle. However, if you are able to land on both your feet and your hands, you have spread that force out over all four limbs, so each limb is taking less force. Then if instead of just landing, you redirect some of that downward force into forward force by rolling, your body will absorb the same amount, but it will do it over a long period of time (the roll) and over a larger part of your body (for instance your back may absorb some energy). This all reduces the peak energy that any single bone is absorbing, and allows you to safely land.

Force = mass times acceleration. It’s important to remember that acceleration doesn’t mean “speeding up”, even though that’s how people often think of it: “acceleration” means “how quickly your speed is changing”.

So, if your speed changes very quickly – say, from “falling down” to “completely stopped” – then you experience a lot of force. But if your speed doesn’t change much – say, from “falling down” to “rolling forwards *almost* as quickly as you were falling” – then you experience a *lot* less force.

Have you ever heard the joke “it’s not the fall that kills you, it’s the sudden stop at the end”? It’s pretty much true. If you roll instead of just landing, though, then there *is no sudden stop*.

You’re transferring vertical velocity into horizontal velocity instead of stopping on landing, which would require the body to absorb the force. You’re at the top of a tall ladder, you jump, you land hard. Put a slide near the bottom of the drop (that looks like a quarter of a circle, but best is parabolic) and you’ll get a little bump as you hit the nearly vertical part of the slide, and you’ll shoot out horizontally unharmed.

Notice they’re running high speed after the land and roll, as they translated the vertical velocity into horizontal. Of course, get that landing just a little off, hit a knee instead of rolling, and you do have broken bones.

Expanding upon OP’s question, what’s the highest one can jump and roll and still go uninjured/survive?