Himalayan porter's specialization: metabolic power, economy, efficiency and skill

Abstract

Carrying heavy loads in the Himalayan region is a real challenge. Porters face extreme ranges in terrain condition, path steepness, altitude hypoxia and climate for 6-8 h a day, many months a year, since they were boys. It has been previously shown that, when carrying loads on level terrain, porters' metabolic economy is higher than in Caucasians but the reasons are still unknown. We monitored Nepalese porters both during 90 km trekking in Khumbu Valley and at two different altitudes (3490 and 5050 m above sealevel), where they were compared to Caucasian mountaineers during (22%) gradient walking. Both subject groups carried a load of up to 90% body mass. The remarkably higher performance of porters during uphill locomotion (C60% in speed, C39% mechanical power) is only partly explained by the lower cost of loaded walking (K20%), being also the result of a better cardio-circulatory adaptation to altitude, which generates a higher mass-specific metabolic power (C30%). Consequently, Nepalese porters show higher efficiency, both during uphill and downhill loaded walking. Their higher economy on steep paths cannot be ascribed to a better exchange between potential and kinetic energy, as in our experiments the body centre of mass travelled monotonically uphill (or downhill). A different oscillation pattern of the loaded head-trunk segment, together with the analysis of the different components of the mechanical work during load carrying, suggests that achieved motor skills in balancing the loaded body segment above the hip could play a role in determining the better economy of porters.

The mechanics of head-supported load carriage by Nepalese porters

“…Our results have been echoed by the on-field load-carrying measurements of Minetti et al (2006) in the Khumbu valley in Nepal. They highlighted the higher efficiency of the Nepalese porters compared with trained Caucasian mountaineers during both uphill and downhill loaded walking.…”

“…2). With the exception of the porters in the low flatlands, the Nepalese typically walk on very hilly terrain where there are hardly ever two steps taken at the same level (Minetti et al, 2006). In preliminary experiments in our laboratory, we have found that a change in height within one step of only 0.09 m (equivalent to a grade of ∼10%) is sufficient to decrease R from 64.4±2.4% to 36.9± 8.6% (mean±s.d., n=12) at ∼1.35 m s −1…”

“…Few studies on the energy consumption and biomechanics of people carrying loads have been published Laursen et al, 2000;Griffin et al, 2003;Minetti et al, 2006). Here, we compare the gait mechanics of the Nepalese porters with those of the African women and Western control subjects with an analysis of the mechanical work and efficiency during walking under different loading and speed conditions.…”

A comparison of the physiological consequences of head-loading and back-loading for African and European women

“…The head strap method has received some recent attention. Minetti et al (2006) concluded that the remarkable capabilities of the Himalayan porters could only partially be explained by metabolic efficiency whilst Malville et al (2001) argued that a combination of pacing strategy and metabolic efficiency contribute to the load carrying abilities of the commercial porters in Eastern Nepal. Both studies seem to support the early findings of Nag et al (1979) who reported this method as being particularly economical when heavy loads are carried at relatively slow speeds.…”

Electromyographic and Cardiorespiratory Responses of Load Carriage at Different High Altitudes with Varying Gradients

“…Indian soldiers are compelled to carry load manually as wilderness of the high altitude terrains construct a critical barrier to the vehicular mode of transportation of load (1). Indian Army deploys more than hundred thousand soldiers in the high altitude border areas.…”