Why you automatically begin to run when you are in a hurry

May 31, 2017 - 06:25

New research shows why the legs change from walking to running when we need to hurry up. The research can be used to help people with paralysis and to create super soldiers, say scientists.

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When you are in a hurry and your legs start to move faster and faster, the body is adapted to automatically switch from walking to running. New research explains how this happens. (Photo: Shutterstock)

We all know what it is like to be in a hurry and suddenly find yourself running.

It is a sudden change from one form of movement to another, and scientists have long puzzled over why we suddenly make this change and when we do it.

A new study, published in the journal Scientific Reports, has an answer.

“A lot happens when we shift from walking to running. Muscles are activated differently, coordination becomes a little bit different. Adjustments are made to make the movement effective and we show in our research when the body makes those adjustments and suggest why it does that,” says co-author Associate Professor Ernst Albin Hansen from the  Department of Health Science and Technology at Aalborg University, Denmark.

Applications for soldiers on long treks

The new research can help people with spinal cord damage—and perhaps also to make better soldiers.

For example,  military organisations around the world are working towards developing an exoskeleton for their soldiers. They seek mechanical, robotic-like solutions that can ease physical exertion during long treks.

Imagine robotic legs outside your own that help you to take steps so that you can carry more weight on your back, or walk longer distances without becoming tired.

Such legs would also help paralysis patients and those with spinal cord injuries to walk.

Both require robot legs that move naturally and can recognise when to switch from a walk to a run.

“These types of legs are controlled by software, which should control the transition between running and walking at the correct time in relation to the person wearing them. This is the transition identified in our research,” says Hansen.

Switches to a run when step frequency increases

The new study shows that the transition between a walk and a run is dependent on the step frequency—the number of steps per minute.

When the average person walks at their preferred way the step frequency is approximately 60 steps a minute. When the same person runs it increases to approximately 80.

The new results indicate how the spinal cord nerves automatically recognises the step frequency, and changes muscle coordination to match the run when it reaches 70 steps per minute.

“It was previously thought that the transition from walking to running happens when it became most energy efficient to run rather than walk. But our research shows that it’s not controlled by energy use,” says Hansen.

Spinal cord keeps the legs going

The new research consider the influence of the networks of nerve cells in the spinal cord—the Central Pattern Generators, or CPGs. These networks are responsible for a large part of the rhythmical movement that the body undertakes without us even thinking about it.

The CPGs coordinate the rhythmical muscle contractions that make one foot step in front of the other without the brain needing to control the movement in detail.

A precise change

When we change from walk to run, we move from one behavioural attractor to another.

Walking uses a behavioural attractor that is strongly influenced by the CPGs, where step frequency stay at around 60, while running takes places at a step frequency of 80.

As we speed up, our step frequency approaches 70 and we approach a running behavioural attractor.

The result is that CPGs change from stimulating muscles to run rather than walk.

“It’s a much more precise change than assuming that we switch from a walk to a run when it’s more favourable energy-wise. Instead it’s these behavioural attractors that reveal when it happens—and this is an entirely new insight into the body’s functions,” says Hansen. 

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Read more in the Danish version of this story on Videnskab.dk
 

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Translated by
Catherine Jex

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