Training for your next marathon, OCR or trail race? Looking to shave off a few seconds from your personal best? Engineering researchers from Stanford University might be on to your new favourite training tool: a rubber band attached to each of a runner's shoes. [Image via Scope]The team of researchers call it the exotendon, an external manufactured "spring" meant to put resistance between strides. The team published their findings recently in the Journal of Experimental Biology. From their abstract:Human running is inefficient. For every 10 calories burned, less than 1 is needed to maintain a constant forward velocity – the remaining energy is, in a sense, wasted. The majority of this wasted energy is expended to support the bodyweight and redirect the center of mass during the stance phase of gait. An order of magnitude less energy is expended to brake and accelerate the swinging leg. Accordingly, most devices designed to increase running efficiency have targeted the costlier stance phase of gait. An alternative approach is seen in nature: spring-like tissues in some animals and humans are believed to assist leg swing... Here, we show that a spring, or ‘exotendon’, connecting the legs of a human reduces the energy required... through a complex mechanism that produces savings beyond those associated with leg swing. According to the team's lead, Elliot Hawkes: "90 percent of the energy you put into running is wasted, in a sense." During the team's tests, they found that the exotendon increased efficiency by over 6%. While no one is recommending you try this at home yet, it surely is an exciting idea from a research point of view. How might this impact training, or shoes and other gear, in the future? To read further details on the experiment, visit Stanford's blog, Scope.