A spring in your step?


In theory, it could make you run an awful lot faster.


A shoe that allows runners to use their legs in the air could considerably increase running speed, researchers say.

Amanda Sutrisno and David J. Braun / Vanderbilt University

A spring-powered device attached to human legs could, in theory at least, boost sprinting speed by more than 50% without external energy input, according to a new US study.

Amanda Sutrisno and David J. Braun from Vanderbilt University say such a (currently hypothetical) device would enable the wearer to supply energy in mid-air by simultaneously compressing and increasing the stiffness of the springs.

During touchdown, the energy stored in the springs would release, redirecting the wearer’s vertical momentum to help propel them forward.

“Our finding uncovers the hidden potential of human performance augmentation via unpowered robotic exoskeletons,” the researchers write in a paper in the journal Science Advances.

“Our result may lead to a new-generation of augmentation devices developed for sports, rescue operations, and law enforcement, where humans could benefit from increased speed of motion.”

Top athletes have clocked a maximum running speed of 12.3 metres per second, Sutrisno and Braun say, but existing spring prosthetics only allow an ordinary wearer to reach around 11 metres per second.

To investigate how to better harness human energy for enhanced running, they used a variable stiffness spring-mass model to predict the maximum speed that augmented humans may be able to achieve without external energy, accounting for air resistance, energy losses during collision with the ground, and the power limitations of limbs.

Next, they predicted optimal relations between running speed, spring stiffness, spring force and ground contact time during high-speed running, then conceptualised a device in which springs support the body rather than limbs, preventing energy losses from contact with the ground, much like wheels support the frame of a bicycle.

There is a catch. Since even state-of-the-art carbon fibre running springs lack the necessary energy capacity, scientists would need to design a novel energy-dense spring to make ultra-speedy spring-powered humans a reality.

However, Sutrisno and Braun say they are encouraged by how much cycling and skating speeds have increased thanks to technological advances.

CREDIT: Amanda Sutrisno and David J. Braun / Vanderbilt University

  1. https://advances.sciencemag.org/content/6/13/eaay1950
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