# The Physics of Free Running

Before you leap, look to Newton

Check out this demo reel of Levi Meeuwenberg doing some jaw-dropping "free running". Free running is very similar to Parkour in the athleticism required and specific techniques and movements used, but while Parkour is about getting from one place to another in as efficient a manner as possible, free running is less directed and more creative in nature.

As mentioned in that ancient post, when performing either of these activities, in addition to spending years developing a formidable set of technical skills, balance, physical strength, and kamikaze attitude, it's important to be cognizant of some basic physics. In order to lessen the impact upon landing after a fall, or to decrease the force upon a set of fingers while grabbing onto a wall, it is essential to reduce the acceleration during each collision as much as possible. This requires increasing the time of impact by smoothly bending, flexing, or rolling during impact.

Let's apply some of the physics by taking a quantitative example. During impact with the ground, there are essentially two forces acting on your body -- the downward force of gravity and the upward force of the ground.

Applying Newton's second law we get:

Fnet = Fground - mg = ma

where mg is the weight force (a.k.a. the force of gravity) acting on your body. So let's say that Levi jumps from a height of 3.0 meters onto the ground. How much force is the ground going to exert on him during impact?

First, let's apply conservation of energy to determine Levi's speed just before contact.
The gravitational potential energy (mgh) due to his initial height relative to the ground is going to be converted into kinetic energy (½ mv2) just before landing. So

Mgh = ½ mv2

and v = [2(9.8m/s2)(3.0m)]1/2 = 7.7m/s

Now we have to bring him to a stop. Let's assume the lithe and wiry Levi has a mass of approximately 70 kg. Now because

Fground = m(g + a) = 70 kg (9.8 m/s2 + a)

we can see that the force of impact depends on the acceleration. But a = Δv/Δt and therefore depends on the time of impact. If he were to foolishly land on his heels with rigid locked knees this would result in a very small impact time -- as little as 0.01 or 0.02 seconds for this type of collision. The result?

Fground = 70 kg (9.8 m/s2 + 7.7m/s/0.01s) = 55,000 N (or about 12,000 pounds). Ouch!

However, by bending and rolling, the time of impact can be increased to as much as 0.3 or 0.4 seconds. By decreasing his velocity over this extended period of time, the force is substantially reduced. Applying the above calculation with an acceleration time of 0.4 seconds we now get Fground = 2000 N (460 pounds). It's still a significant force but as you can see in the video quite manageable for someone with the proper skill, strength and technique.

Speaking of landing on the heels, notice that Levi never does that. Impacts are always taken with the ball of the foot. Landing on the ball allows for an increased impact time and less compression on the legs. Now recall some previous posts on running shoes.

Did we not decide that the most efficient stride technique involved a mid- to fore-foot strike? It seems reasonable to propose that the most efficient stride is also the most natural stride for the running human, and might be expected to result in fewer injuries, relative to the much more jarring heel strike. Most running shoes have big padded heels, making it easy for the unwary jogger to strike with the heels. However, running barefoot, it's relatively impossible to do that. It's just too painful. You automatically impact on the front of the foot, much like Levi does when sticking a landing. Interesting. We've talked about a pair of shoes meant to simulate barefoot running. But what about the real thing? What about barefoot running itself?

To be continued...!

Adam Weiner is the author of Don't Try This at Home! The Physics of Hollywood Movies.

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Absolutely superb article. I'm a freerunner and I would like to say that you have everything right. I would go so far to say that this is the best article written I've seen.

I'm sure I could do all that stuff... on the MOON... well maybe I still couldn't do the physics lulz. I watch this stuff and think people cant do that but at the same time I kinda want to do it as much as much as flying. Go back 300 years with that skill and people would be sure you could fly.

Barefoot running? It's pretty common in the public schools in the Philippines. Those barefoot kids can run faster than those with running shoes. The callous of their feet are as thick as hell. Impressive what mother nature can do.

Amazing stuff! Key point to remember though, this is for someone with the proper skill, strength and technique. There are several YouTube examples out there when you search on Parkour demonstrating that the faceplant landing technique is not the best landing either. Big Wow sometimes equals Big OW!

I, like SilverCrusader, practice parkour/freerunning. You get much more out of it than just fitness. It is also a huge community in which people help each other and in which there is little to no competition. I'm part of a branch of Aero Parkour in Chicago called Aptera Parkour. (Aptera means Wingless Flight.)

The good thing about freerunning IMO is it's bringing back gymnastics, which was a dying sport. Even though there are amateur kids practicing parkour, by far the ranks of the people who can actually do interesting things are filled with those with gymnastics background. I remember even a few years ago when I was getting out of this stuff, the adult sessions at a gym I frequented were getting more and more tricksters/parkour guys compared to people doing traditional gymnastics. Hopefully the USGA will do something with this to bring gymnastics back into popularity

Hopefully not. Freerunning is not gymnastics. It is by no means a sport. There is nothing about freerunning that can be used to bring up the popularity of gymnastics. Freerunning is it's own discipline entirely.

Oh that I was of the physical prowess to preform such stunts! Those are amazing to watch. It's as though gravity lessens slightly each time a trick is preformed (for preformed they were). I applaud SilverCrusader and pdashby for their hard work and effort that has undoubtedly gone into their field of expertise. Freerunning Rocks!

As a barefoot runner for nearly 8 years I can confirm that barefoot running kept me injury-free, healthier and enjoying running. However, barefooting isn't always applicable. Extreme weather or unknown/unpredictable surfaces can make it difficult. I knew immediately that a '2nd skin' type anti-shoe shoe would be beneficial in cold Alberta winters. That led me to begin developing Skora (www.skorashop.com) - a minimal footwear product company to aid the transition to barefoot running.

Happy trails,

David Sypniewski
Barefoot runner & Instigator since 2002
www.barefootrunner.com // natural running blog

Thanks for the superb article. The stunts done in the video are really tough. Parkour is mainly practiced by the youngsters for obtaining a fit body. It focuses mainly on running, jumping etc. You need to practice a lot for being a master of Parkour. For more details refer www.zippy-health.com/parkour-the-current-fitness-craze/

thanks dude!

Don't Try This at Home! The Physics of Hollywood Movies.

Can anyone make these formulas become something that I can touch?
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That project just on the table?
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phenomenal work. Thanks a million. I have read plenty of article but never crossed like such an article with tons of information that are very useful.

Great article. I was always amazed by all they can do while maintaining their bodies injury free. Now I understand how they get away with so much freedom of movement.

Very exciting to see how free running/parkour have influenced fitness as well as the most popular bootcamp exercises and programs out there right now.

MNeave, CFT
Fitness Editor
www.freeworkoutsguide.com/bootcampexercises.html

I would go so far to say that this is the best article written I've seen.good thing!!thanks for sharing

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Wow! I personally have not heard of this before seeing this vid. I must comment though, strong toning shoes, or comfortable joggers that have a significant support is without question a prerequisite for this enduring activity.

www.comfortablefoot.com

I stopped watching the annoying video with an advertisements every few seconds. I boycott brands that are that abusive. I never got to read the article.

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