When running is like falling

Norwegian physicist proposes way to run faster, using gravity

Photo: Beat / Wikimedia Commons  The finish of the women’s 100 meter sprint at Golden League 2007, Zurich. Are these runners jumping or falling?

Photo: Beat / Wikimedia Commons
The finish of the women’s 100 meter sprint at Golden League 2007, Zurich. Are these runners jumping or falling?

M. Michael Brady
Asker, Norway

Running is said to be the world’s oldest and most accessible sport. It also may be the most studied. Ever since the first Olympics were held in 776 BC, the question of why some people run faster than others has been pondered by philosophers, scientists, and in the last two centuries, by runners and their coaches. So when an article on a new theory of running was published in September 2015 in the Proceedings of the Royal Society, the world’s oldest learned society for the sciences (founded in 1660), it made news around the world.

The article by Norwegian physicist Svein Otto Kanstad and Finnish physiologist Aulikki Kononoff (Further reading), both former competitive runners, flies in the face of conventional wisdom on how high speeds in running are attained. Its title, Gravity-driven horizontal locomotion spotlights the essential distinction between it and older theories of running.

In most theories of running, gravity is not considered to be a force helpful in forward propulsion, as it is perpendicular to the direction of motion of the runner. Moreover, gravity often is seen as the enemy of the runner, as the force of it is involved in the risk of injury in shock absorption as feet strike the ground.

Physicist Kanstad explains that gravity should be included, not excluded from the theory of running. In a stride of walking or running, humans essentially fall forward and rotate around a supporting foot. Gravity then imparts angular momentum rotational energy to the runner’s body. This momentum and energy may then contribute to forward propulsion when landing on the other foot. Theoretical studies have shown that 10% or more of the energy involved in running may come in this way from the field of gravity. Experimental tests with athletes walking and running on a treadmill confirmed the theory.

In short, running should be thought of not as a sequence of jumps off one foot and landing on the other, but rather as a sequence of falls, induced by gravity. Runners will need to alter their gait to benefit from this line of thinking. They will need to pull the trailing leg forward more rapidly instead of letting it trail, stretched out behind when the foot of the leading leg contacts the underlying surface.

The new theory has already been proven in practice. Famed American sprinter Michael Johnson, who won many medals, including four Olympic and eight World Championship gold medals, before retiring after the 2000 Sydney Olympics, runs with a gait in conformance with it. Moreover, it might explain why humans have been able to outrun larger prey to exhaustion in hours of hunting pursuit. It may also contribute to the understanding of the mechanics of walking and hence benefit the design of leg prostheses and exoskeletons.

Further reading:
“Gravity-driven horizontal locomotion: theory and experiment,” by S.O. Kanstad and A. Kononoff, Proceedings of the Royal Society, 16 September 2015, free online via International DOI Foundation at www.doi.org, submit document name 10.1098/rspa.2015.0287, or directly to the Royal Society at: rspa.royalsocietypublishing.org/content/471/2181/20150287.

This article originally appeared in the Dec. 11, 2015, issue of the Norwegian American Weekly. To subscribe, visit SUBSCRIBE or call us at (206) 784-4617.

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