Nepalese porters bear up best
African women pipped to the post for most efficient portering.
The porters of Nepal are famous for being the most spectacular haulers of head-supported loads in the world. They trek up and down steep mountain trails, sometimes for hundreds of kilometres, while carrying goods in a basket supported by a strap across their foreheads. Often the loads exceed the porter's own body weight.
A study in this week's Science shows that Nepalis carry loads more economically than any other group previously studied1. They expend less energy per load than both Westerners with backpacks and African women who carry baskets on their heads, either directly or with a strap.
The team, led by Norman Heglund, a physiologist at the Catholic University of Louvain in Belgium, are not sure exactly how the porters manage to be so efficient. It is known that they usually walk with a slow pace and take frequent breaks, sometimes resting for 45 seconds out of every minute on a steep climb. But the porters are also efficient when walking at a steady pace, the team found. Perhaps they alter their gait to somehow reduce muscular work, the researchers guess, or in some other way increase their efficiency.
Heglund and his colleagues travelled to Nepal and watched porters carrying their loads up to a weekly market at the town of Namche. They asked a selection of these porters to walk around a flat track at various speeds while carrying several different loads. The energy expended by these individuals was determined by measuring their oxygen consumption and carbon dioxide production through a mask.
The team then compared the results with work on women of the African Kikuyu and Luo tribes. These women can carry head loads of up to 20% of their body weight without expending extra energy. Additionally, they carry loads of up to 60% of their body weight at a considerably cheaper metabolic cost than army recruits carrying equivalent backpack loads2.
At light loads, the Nepalese porters and the African women were about equally efficient. But the heavier the load, the better the Nepalese became at expending minimal energy.
Heglund and colleagues have previously shown that the African women conserve energy by swinging their bodies like a pendulum3. But the Nepalese porters had a different gait. "They didn't use the same energy saving mechanism as the African women," says Heglund. The team plans to study this next.
- Bastien G. J., Schepens B., Williems P. A. & Heglund N. C. Science, 308. 1755 (2005).
- Maloiy G. M. O., Heglund N. C., Prager L. M., Cavagna G. A. & Taylor C. R. Nature, 319. 668 - 669 (1986).
- Heglund N. C., Willems P. A., Penta M. & Cavagna G. A. Nature, 375. 52 - 54 (1995).