For centuries, Nepali porters have made a name for themselves carrying enormous loads on their backs using just a namlo (headstrap) on their foreheads. But many people are baffled by how they manage to sustain themselves for hours and hours.
Obviously lowland porters carrying heavy loads face immense difficulties at high altitude. These problems need to be addressed effectively so that porters do not suffer from life-threatening mountain sickness and frostbite. However, today's article will focus on the physics and physiology behind Nepali porters' ability to manage the big burden on their shoulders.
An interesting study conducted by Norman Heglund et al a few years ago showed that African women carry loads on their heads more efficiently than US army recruits carry heavy backpacks. The investigators used African women's ability to conserve mechanical energy and the "improved pendulum-like transfer" during each step to explain the differences. The physics was hard to understand for novices, but scientists felt the explanation was adequate.
The same investigators came to Nepal around eight years ago to see how efficiently Nepali porters carried their load. The results were fascinating.
At an altitude of about 3000m, Nepali porters were asked to walk around a 51m track at five different speeds carrying six or seven loads according to their ability. Then the energy cost of carrying these loads was determined by measuring the amount of oxygen consumed and the amount of carbon dioxide exhaled using various instruments.
When the researchers compared the results with the studies done on Europeans, marine recruits and African women, they found that Nepali porters were far more efficient. They carried loads which were 30 per cent heavier than the maximum load carried by African women for the same increase in metabolic rate.
The physics and physiology behind our porters' ability to carry large weights are still not completely clear. But one of the tricks our porters use is to take frequent breaks while going uphill which reduce muscular work and increase overall efficiency.