Humans walk on virtual length legs.

While many of the athletes that line up for one of the planet’s great marathon races will be sporting the latest high-tech footwear, an increasing number of running enthusiasts are casting aside their Nikes and Asics in favour of a more free style of running. Preferring to run barefoot, these athletes land on the balls of the foot rather than striking the ground heel first. ‘I’ve been a barefoot runner for about 12 years’, says James Webber from the University of Arizona, who explains that his passion took him to graduate school to learn about the evolution of human running. However, something bothered Webber. ‘In running, people can change foot postures and it does not seem to change energetic costs very much’, he says – which made him wonder: why are we so locked into landing on our heels when we walk?