[NEW DELHI] The method Nepalese porters use to carry nearly double their own weight — by strapping loads to their head, walking slowly for many hours and taking frequent rests — is most efficient in the world, say scientists.
The porters can carry up to 20 per cent of their weight 'for free', using no more energy than if they were carrying nothing.
The researchers, led by Norman Heglund of the Louvain Catholic University, Belgium, calculated the energy efficiency of eight Nepalese porters who regularly walk from the capital, Kathmandu, to a market town near Mount Everest.
The distance of the weeklong journey is 100 kilometres, with total ascents of 8,000 metres and descents of 6,300 metres.
Heglund says the Nepalese porters — male and female — carry heavier loads more efficiently than African women, previously thought to have the most efficient carrying method.
Previously, Heglund and colleagues showed that Kenyan women could carry head-supported loads of up to 60 per cent of their body weight far more efficiently than army recruits carrying similar loads in backpacks.
The new findings, published today in Science, show that the Nepalese porters carry loads that are, on average, one-third heavier than the heaviest loads that African women carry using the same amount of energy.
Nepalese porters use a head strap (locally called a namlo) to support a basket (doko) containing a load that can be nearly twice their body weight. They also use a T-shaped stick (tokma) to support the load while taking rests.
Heglund told SciDev.Net that the porters spent only half the energy that European trekkers carrying backpacks used when either carried more than half (60 per cent) of their body weight.
The eight porters were selected from a stream of porters regularly going up and down the steep Himalayan mountain route.
They were asked to walk a 51-metre long flat track at five different speeds, carrying six or seven loads according to their ability. The researchers measured the amount of oxygen they used and how much carbon dioxide they exhaled.
The team wasn't able to say whether the porters are able to reduce the work their muscles do to carry the loads, or if they increase their overall efficiency.
Heglund points out that professional porters and load carriers around the world carry loads on their heads. Porters in the Andes mountain range of South America and workers in construction sites across India use it as well.
Despite the porters seeming efficiency — Heglund, for example, saw a 68-year-old porter carry loads heavier than himself — they face several health risks during their arduous treks, whether in the Himalayas, the Inca Trail in Peru or Mount Kilimanjaro in Tanzania.
International charities such as the UK-based International Porters Protection Group (IPPG) and Tourism Concern conduct campaigns to raise awareness of the problems, because many porters take part in tourists' trekking expeditions. The problems include risks of slipping and injuries, frostbite, and altitude sickness.
“Unfortunately, while we agree that many porters do perform some pretty amazing feats of strength, there are also porters injured, maimed or losing their lives each year due to the accumulative physical stresses placed upon their bodies,” says Elsie James, a Canada-based member of IPPG.
The Nepal chapter of the UK-based Intermediate Technology Development Group (ITDG), which helps people use appropriate technologies to fight poverty, says its future plans include studies on socio-economic aspects of heavy load transport by porters in the Himalayas.
So far ITDG in Nepal has been working on alternate means of transporting goods such as wire bridges to cross rivers, Anil Subedi, director of ITDG in Nepal, told SciDev.Net.
Other means of transporting goods in mountain regions include mules, the jhopa — a local cross-breed between the yak and mountain cattle — sheep and goats.
Link to full paper in Science
Reference: Science 308, 1755 (2005)