The Physics of A Human Landing and Rolling

[grantparkour]

HI there, I'm a practicioner of Parkour, which is a discipline that involves training to allow yourself to pass any obstacles simply using your body.
One of the movements which we use is a roll, designed to aid landing from height.

As I understand it, the basic idea is that the roll disperses the force exerted on your body from the impact and prevents the force being focued on a specific place and causing damage.

Basically If I was wondering if anyone could offer a more full explanation of why this roll is a much better way to take the impact of a drop than simply land.
A few guys on my parkour forums don't seem to buy it into it, whereas it's use seems obvious to me. I figured if I can get some scientific evidence they might start to understand it's use.

This is a video of footage of rolls performed by one of the originators of the sport, as an example:
http://uk.youtube.com/watch?v=rekmYbFRbK0
(as a quick disclaimer, the drops etc in this video are really huge - this guys has been doing parkour for 20 years - I don't perform movements that high!)

This is my local parkour website, if you would like any more details:
www.glasgowparkour.co.uk



Thanks for any help,
Chris Grant

 

[arivero]

Wow! It is as some of these martial acts based on projections.

I think you should not consider only force but also energy. Energy and momentum are the preserved quantities, what means they are the ones you must produce or, in this case, absorb (the force of gravity acting on the body produces for free this energy and momentum). The roll permits the forces to be distributed around all the body and around time, so no part of the body suffers any point force beyond the body "break limits". At all, it is about not breaking structures (er, human bodies), so it is something between physics and engineering.

 

[rcgldr]

The main thing the roll does is to give the person's center of mass more distance to decelerate when landing and therefore reduce the rate of deceleration. If there's no forward speed in the drop, the methods shown in the video would have to be modified.

On a competition trampoline, with its adjacent pads, where head impact isn't an issue, the feet are positioned forwards with the knee joints bent and relaxed, resulting in a back roll or energy killing back flip. This wouldn't work on hard ground because of the head impact speed.

 

[cesiumfrog]

If there's no forward speed in the drop, the methods shown in the video would have to be modified[..] resulting in a back roll

Yeah, concerning the physics it's basically a flashy "parachute roll". (Incidentally, being more diagonal than a somersault gives the neck some protection.)

In addition to (as Jeff said) lengthening the distance over which you decelerate, it also spreads the force over more of your body: instead of directing all of the energy into your legs (compressing them beyond the point where something breaks), in a parachute roll you (afterward) let yourself topple back onto your side (letting the energy dissipate from your legs) and spreading the force of the remaining impact over the entire length of the body (like a "break fall").