Have you ever marveled at how characters in movies like brick estate, Assassin’s Creed and Casino Royale? These are not special effects.
The athletes who perform these stunts practice parkour, an activity practiced around the world close to gymnastics. This sport evolved from military obstacle courses. The goal of parkour is to move quickly and efficiently through a complex physical environment.
Our research shows that science can help make parkour better by explaining how to climb walls more effectively and expand landing opportunities. Even if you don’t plan to play this sport, it’s an amazing experience to watch.
tracers and plotters
Although parkour has been recognized as an official sport in some countries, it is still impossible to determine how many people practice it worldwide. It’s a generally disorganized activity, perhaps part of its appeal as a subculture.
To an inexperienced observer, parkour athletes — known as “tracers” and “tracereuses” — may seem downright ruthless, but most of them train hard and develop a wide range of individual skills that they use as they navigate their environments.
Some of the individual movements in parkour are similar to those in other sports such as gymnastics, track and field, and trail running. But parkour has been much less explored than other more traditional sports. This is unfortunate as these sports share basic principles of generating and redirecting momentum, or more accurately “momentum”. A better understanding of these principles can benefit all these activities.
Walk along the walls
One of the feats that catches the attention of many parkour viewers is how traceurs run along high walls to conquer new buildings.
To scale tall structures, parkour athletes run towards the wall and then gain height by projecting their body upwards by pressing against the wall with their feet. This technique allows them to reach much greater heights than with a vertical jump, and also allows them to continue to move efficiently through urban space.
To study how effectively athletes perform this wall run, we embedded one force plate (a device used to measure the force applied to it) in the floor and a second force plate in the wall. We then filmed the participants as they approached the wall.
We observed how the athletes redirected their bodies with a consistent overall strategy and targeted leg actions on the floor and wall.
Although some parkour guides recommend that athletes lean on the floor and wall at the same time, we disregarded this – traceurs always left the floor before hitting the wall.
We wanted to better understand the most efficient placement of feet on the floor and on the wall, and the effects of different approach speeds. We have therefore created a computer simulation capable of optimizing each of these factors.
The model fits well with what we observed – a medium approach speed is best – and allowed us to understand why.
Running produces horizontal momentum (the product of speed and body weight). Some of this horizontal momentum can be redirected to vertical momentum at takeoff, keeping the leg rigid on the ground—similar to pole vaulting with a rigid pole.
If the approach is slow, there is less horizontal momentum that can be translated into vertical momentum. The take-off leg then has to use the leg muscles to generate vertical momentum, which is less efficient.
On a very fast approach, the launch leg must act as a shock absorber, wasting energy and negating the benefits of running fast.
Tracers therefore naturally choose a medium approach speed, which allows them to scale the wall with as little energy as possible.
Climbing higher walls may require faster access, but sufficient leg strength is required. Higher speed gives more momentum, but also decreases the time it takes for the leg to generate the “momentum” needed to climb the wall – this is the change in momentum, mathematically the product of force and time.
Return to the ground
What goes up must come down!
To jump off a wall, traceurs choose a type of landing based on their height, body mass, and leg strength, our research shows.
A safe landing requires dealing with several different forces. When descending or jumping from a surface, the body accelerates due to gravity. When landing, the body has some movement determined by weight and speed. The higher the surface you jump from, the greater the speed and amount of vertical movement before landing.
The main task when landing is to dissipate momentum so that pressure and speed do not exceed biological limits (resulting in muscle tears or tendon ruptures).
The amount of this momentum to be dissipated can be reduced by increasing the time that the landing forces are applied, for example by bending the legs.
It is also possible to redirect the force by converting the amount of vertical movement to rotational movement with a pulley. This means power is directed to limit injury.
The strategies used vary according to body characteristics such as height, weight, bone and joint strength, muscle strength, flexibility and coordination. If the chosen strategy is not sufficient to manage the swing, injuries (muscles or bones) will result.
Roll to protect yourself
As you might expect, our research shows that after a higher fall, you’re more likely to roll. The subjects in our study (nine men and two women) were between 1.58 and 1.87 meters tall and weighed between 54 and 92 kilograms.
At certain altitudes, a two-legged landing is not possible. But in this study, the maximum fall height was only 2.4 meters, and some tracers chose not to even go that height.
People with long legs can exert lesser force for longer periods of time by gradually bending their legs to gain momentum while shorter tracers roll for lower altitudes.
Heavier people have more momentum than lighter people when falling from the same height. We’ve found that this affects the likelihood of a roll – heavier athletes are more likely to choose to roll when falling from lower heights.
Athletes with greater leg strength absorb momentum with their legs to a greater drop height, and athletes with less leg strength typically switch to a roll landing at lower heights.
If you can’t change the size, you can adjust body mass and leg strength through training. In practice, this gives more flexibility to choose a landing strategy depending on the situation, rather than being forced to roll to dissipate momentum.
This review was written by James L. Croft, Senior Lecturer in Motor Acquisition and Control at Edith-Cowan University (Australia).
The original article was translated (from English) by Malik Habchi and then published on The conversation.