Optimal rate of work for mountaineers.

The physiological responses of seven young male highlanders were recorded at high altitude while they were carrying loads (0, 25, 35, 45, and 55 kg) on snow at different speeds, supporting the loads on their backs by circular straps around the forehead. The rates of work calculated from the gross weight (body weight plus actual load in kg) multiplied by the speed of walking, m.min-1, ranged from 4,460 to 8,440 kg.m.min-1. The relationship between the rate of work and energy expenditure was rectilinear within the present range of values. The oxygen consumption (51.6 and 59.7 ml.min-1.kg-1 BW) for 55-kg load (at 4.09 and 4.64 km.h-1) possibly reached maximal aerobic capacity. At higher energy output at high altitude the subjects were exhausted after a short period of work. The proportion of increase of oxygen consumption per kg gross weight carried or per kg.m was almost constant up to a 55-kg experimental load. It is suggested that for day-to-day operations work should not be undertaken at more than 30-40% of maximal work capacity; a rate of work around 4,000 kg.m.min-1 (25-30 kg actual load at 3.0 to 3.5 km.h-1) may be considered as optimal for highlanders and porters at high altitude.