# What could Usain Bolt do faster?

In the final of the 100-meter run at the Olympic Games in Beijing in 2008, Usain Bolt not only improved his own world record over this distance. He also reached a top speed of 43.9 kilometers per hour - making the Jamaican the fastest man in the world. So far. Because a research group at Vanderbilt University in Nashville, Tennessee, is working on a shoe that will set new racing records. David Braun, assistant professor for mechanical engineering and technical informatics, explains how he came up with the idea of ​​making a person run at 80 km / h.

SZ: Mr. Braun, how fast are you a hundred meters?

David Braun: I'm not a sprinter, I'm a jogger. I've run marathons before, but I'm probably very average at a hundred meters.

Her research shows that people should theoretically be able to run up to 80 km / h.

The starting point of our research was the question: Why is the top speed on a bike about twice as high as in a race? In both cases, after all, the engine is the human being. And when you think of the first bicycles that were made in the mid-18th century - they were balance bikes. There were no pedals yet, the feet touched the ground. Today, the top speed on a bike is around 80 kilometers per hour, that of the fastest person in the world is just under 44.

How can the difference be explained?

Let's go back to our first balance bikes: They already had the advantage that the bikes mitigated the impacts and energy losses that occur when the feet come into contact with the ground. But the decisive factor was the invention of the pedal logic - this was the only way to achieve a speed advantage over racing. The pedals allow continuous movement of the legs. The legs are bent all the time, propelling the body forward. In contrast, when running, your legs are useless while in the air. To put it in percentages: The fastest person in the world can use their legs in 20 percent of the time, when cycling we are at 100 percent.

This is where your invention comes in?

We want to transfer the mechanics of cycling to walking. We are currently developing the prototype. We use a programmable spring to ensure that the legs can also work in the air. The resulting energy is collected and released the moment the feet touch the ground. For starters, I imagine a kind of exoskeleton - that is, rails that are strapped around the legs. But in the long run the idea is to downsize the system so that it fits in a shoe.

So I run at 80 km / h - how do I brake?

Just like you would brake in a normal run: by stepping back with your upper body and moving your legs more slowly. It is conceivable to install a kind of gearshift - the up and down shifting could either be activated with a wristband with a finger movement or it could be fully automatic. But of course you will have to learn to run in these shoes, just as every child has to learn to ride a bike first. The forces that act on the body are more powerful. And the single step gets bigger: you will probably stand a little higher in the air and be pushed a little further forward. But the example of the ice skates shows us that it can work.

What do you mean?

Ice skates have created a whole new form of movement. Ice skating is not like racing. The best speed skaters can cover 15 meters per second - so humans are basically able to use such devices.

You see police work as a possible area of ​​application for your shoes.

One disadvantage of the bike is that it's not really suitable for the city. What if a fugitive runs up a flight of stairs? Or sprinting over an uneven meadow in the city park? Our shoe could give the officers an advantage here - it should be able to be used regardless of the terrain. However, it will never be able to replace a certain basic fitness.

Do you have to be athletic to wear it?

The engine is still the human being. Our shoe does not replace muscle power, but uses it more effectively than our body can alone. That is why only one Usain Bolt will be able to reach 80 kilometers per hour.

How long will it be before we can buy your shoe everywhere?

It took 150 years from the invention of the balance bike to the racing bike. Hopefully we won't need that long.