http://news.nationalgeographic.com/news/2005/06/0616_050616_nepalporter.html

Ben Harder
for National Geographic News
June 16, 2005

If you've ever watched Nepalese porters in action, you might think they have superhuman strength. How else to explain their ability to carry loads weighing more than 100 pounds (45 kilograms), mile after arduous mile over steep Himalaya terrain?

Now scientists say they have a clue as to how the porters do it: They use less energy than other people would require for the same work.

Norman Heglund, a physiologist at Catholic University of Louvain in Belgium, led the study, which was sponsored in part by the National Geographic Society Committee for Research and Exploration.

Twenty years ago Heglund studied African women in Kenya—who often balance loads atop their heads—to investigate their unique burden-bearing efficiency.

His latest study, which appears tomorrow in the journal Science, now suggests that the porters of Nepal are even more efficient at their tasks. Precisely why, however, remains a mystery.

So legendary are the load-carrying abilities of the Nepalese that the word Sherpa, a term for one of the country's ethnic groups, has become synonymous with "porter."

A typical Nepalese porter carries a load nearly as heavy as he is. When he does, the porter burns less energy per pound than a backpacker would need to shoulder about half the same weight, Heglund and his colleagues found.

That remarkable ability helps porters to earn a living carting goods great distances between markets in the Himalayan nation. A weekly bazaar in the market town of Namche, for example, serves a gathering point for merchants from all over the Mount Everest region.

"Often, you see husband-and-wife trekking teams," Heglund said. Porters stock up on goods in the Kathmandu Valley and carry their loads from dawn to dusk over the course of a week or more to reach Namche, which sits at 11,500 feet (3,500 meters).

En route, the porters traverse more than 60 miles (100 kilometers) along rugged footpaths. During the journey, they climb some 5 vertical miles (8 kilometers) and descend about 4 miles (6.5 kilometers).

After the porters sell their goods in Namche, they race home unencumbered for more cargo.

"They literally run down the mountain," Heglund said. "They can get home in about two days."

Tons of Cargo

During their field research, Heglund and his teammates flagged down porters and weighed the loads of study volunteers on the approach to Namche one day. More than 500 men and about 100 women carried about 30 tons of material to the market that day, the researchers estimated.

On average, the men and women respectively bore 93 percent and 66 percent of their body weight, the researchers report.

"It's quite impressive to see those guys walking with such heavy loads," said Heglund's teammate Bénédicte Schepens. She added that the feat is particularly impressive because "they're [generally] not very well equipped [and] have very bad shoes."

A porter's gear is simple but effective: The load goes into an oversized basket, or doko, which rests against the back. A strap runs underneath the doko and over the crown of the head, which bears most of the weight. Each porter also carries a T-shaped walking stick called a tokma.

When on the move, porters sometimes pause more than they walk. "On a steep incline," Heglund said, "they'll walk for as little as 15 seconds and rest for 45." At each stop, they use their tokma to support their load, which allows a standing rest.

A Good Puzzle

Around the world, many people use their heads to bear burdens, said Rodger Kram, an expert on human and animal locomotion at the University of Colorado in Boulder. "It's amazing how universal carrying loads on the head is—except in Western Europe and North America," he said.

But their "enormous loads" set the Nepalese apart, Kram added. "It's a good scientific puzzle, how they [conserve] energy when walking."

The researchers behind the new study haven't fully pieced it together.

African women use a particular gait to conserve up to 80 percent of each stride's momentum, Heglund has found. But it only works on flat ground, and there's little of that in Nepal.

Heglund said the porters' "energy transfer is about 65 percent, the same as you or I." That may be. But they certainly don't struggle beneath their burdens as the rest of us might.

There might actually be something to be said for the efficiency gained by carrying heavy loads on one's head.

I'm not believeing that though, until I see some muscle-strength data or something. The porters grew up in that terrain and worked very hard even as kids.