When the going gets tough, the tough use their heads. Porters around the world carry loads that would floor backpackers by balancing baskets atop their noggins or slinging sacks from their craniums. Now a new study reveals that Nepalese porters do the job better than anyone else, hefting huge bundles while using relatively little energy.
Until now, the most economical head-carriers were thought to be African women. A 1995 study by physiologist Norman Heglund of the Catholic University of Louvain in Belgium and colleagues suggested that the women use a special spring in their step that enables them to conserve energy while transporting loads across level ground. However, no one had rigorously tested the energetics of Nepalese porters such as Sherpas, a group known for their role in Mount Everest expeditions. The men on average carry nearly their own body weight in goods, hauling everything from rice to televisions for up to 100 kilometers along steep dirt paths.
Heglund and colleagues tested the Nepalese porters by weighing their packs and measuring how much oxygen they used up and how much carbon dioxide they blew out, numbers directly related to how many calories they burn. Compared with backpack-carrying control subjects, the Nepalis used significantly less energy. For smaller weights, up to 20 percent of their body mass, the Nepalis were as efficient as the African women: Both walked as if unburdened. But as the weight piled on, the Nepalis showed even greater economy, Heglund and colleagues report 17 June in Science. Unlike the African women, though, the Nepalis do not appear to use a special step, so their economical walk is still a mystery. It's probably the sum of a lot of little effects learned over years of practice, Heglund says.
"It is a nice piece of research, confirming that loaded walking can be improved, as opposed to normal walking which is already metabolically optimal," says biomechanist Alberto Minetti at Manchester Metropolitan University in Cheshire, U.K. He believes the Nepalis may economize the internal work their muscles do in stabilizing the trunk of their bodies when loaded.