Their combination of technique and physical ability makes their performance far more effective than that of Western soldiers marching with backpacks, according to research. It even surpasses the most efficient carrying methods studied to date: those of African women whose loads are balanced on or suspended from the head.

A study by Belgian researchers has quantified the remarkable efficiency of Nepal’s porters, most of whom come from the sherpa, Rai or Tamang ethnic groups, for the first time. They carry huge loads in a basket known as doko, which is supported with a strap looping around the top of the head.

A team led by Norman Heglund of the Catholic University of Louvain, in Brussels, conducted tests on eight porters travelling to a bazaar in the town of Namche, which lies 3,500m (11,500ft) above sea level close to Mount Everest.

The dirt-track route from the Kathmandu Valley to Namche covers 62 miles (100km), with combined ascents of about 8,000m and descents of about 6,300m, and takes seasoned porters between seven and nine days to complete. Hundreds of porters make the trek every week; on the day before the bazaar, the scientists counted 545 men and 97 women, along with 32 yaks, with many more passing earlier and later in the darkness. The youngest porter was 11 and the oldest 68.

All were carrying loads that seemed unfeasibly heavy to Western observers. The men bore an average of 93 per cent of their bodyweight and the women an average of 66 per cent. A fifth of the men were carrying 125 per cent of their bodyweight and one managed an astonishing 183 per cent.

By contrast, the greatest loads carried by African women, such as those of the Kikuyu tribe in Kenya, amount to 60 per cent of bodyweight, and the loads typically included in military backpacks are lower still.

Dr Heglund, whose results are published today in the journal Science, recruited eight of the porters for further investigation, which has shed some light on the nature of their amazing skills. The porters were asked to walk along a 51m flat track at five different speeds, carrying six or seven different loads, while their oxygen intake and carbon dioxide output was measured.

The tests revealed that loads of up to 20 per cent of bodyweight were carried “for free” — meaning that the porters’ metabolic rate did not increase at all compared with an unladen walk. With higher proportional loads, their energy efficiency was far greater than seen with the most efficient head-based carrying techniques used in Africa.

Previous research comparing Kikuyu women with army recruits found that the former carried heavy loads much more efficiently. For loads of 20 per cent of bodyweight, Kikuyu oxygen consumption rose 2 per cent compared with 13 per cent for the soldiers. The difference was even greater for 70 per cent loads: the soldiers used 100 per cent more oxygen, but the women only 50 per cent more. The porters did even better. While they were not subjected to quite the same tests, they were able to carry an extra 30 per cent of bodyweight, on average, while maintaining the same metabolic rate.

Their secret seems to rest on three factors. The first is physiology: the combination of a short but powerful stature and a high red blood cell count evolved as a result of living at high altitude. Also critical is their carrying technique, by which a strap around the head bears the majority of the load. The final element seems to be the regular rests that they take during their climbs.

TAKING THE STRAIN

SHERPA

Technique: doko basket on the back supported by namlo strap around head

Load and efficiency: male porters carry average of 93 per cent of bodyweight, females 66 per cent. Maximum was 183 per cent. Can carry 100 per cent of bodyweight for same energy used by an African woman carrying 70 per cent

AFRICAN WOMEN

Technique: loads balanced on the head or suspended from it using straps. The most efficient method, used by the Kenyan Kikuyu, uses bindings across the forehead to support a load on the back

Load and efficiency: Loads do not generally exceed 60 per cent of bodyweight

SOLDIER

Technique: backpack with shoulder and waist straps

Load and efficiency: US Army guidelines say that a backpack should weigh no more than 15 per cent of a soldier’s weight. A 70 per cent load raises oxygen consumption 100 per cent

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