Background: The present study was designed to evaluate load carriage performance at extremely high altitudes with different loads and walking speeds in terms of physiological evaluation. The degree of maximum oxygen consumption changes at high altitudes was also examined.Methods: Twelve Indian Army soldiers were acclimatized at altitudes of 3,505 m and 4,300 m. They walked for 10 minutes on a motorized treadmill at 2.5km/h and 3.5km/h speeds during carrying no loads and three magnitudes of load(10.7kg, 21.4kg, 30kg) at both altitudes. Physiological parameters such as oxygen consumption, energy expenditure, heart rate, and ventilation were recorded for each breath using a gas analyzer. The rating of perceived exertion was also noted after each load carriage session. Maximal oxygen consumption(VO2max) was measured at sea level and the two high altitudes, and respective relative workloads(% of VO2max) were calculated from oxygen consumption. Repeated measure ANOVA was applied to reveal the significant effects of the independent variables.Results: The participants had significant reductions in VO2 max with rising altitude. Marked increases in almost all physiological parameters were observed with increasing load, altitude, and speed. The soldiers expressed heavy perceived exertion levels with higher loads at 3.5km/h at the two high altitudes.Conclusions: Considering the physiological responses, expressions of perceived exertion and changes in relative work load at both of the high altitudes. Indian soldiers are advised to walk slowly with adequate rest in between their schedules and to carry not more than 32% of their body weight. Background: The present study was designed to evaluate load carriage performance at extremely high altitudes with different loads and walking speeds in terms of physiological evaluation. The degree of maximum oxygen consumption changes at high altitudes was also examined. Methods: Twelve Indian Army soldiers were acclimatized at altitudes of 3,505 m and 4,300 m. They walked for 10 minutes on a motorized treadmill at 2.5 km / h and 3.5 km / h speeds during carrying no loads and three magnitudes of load (10.7 kg, 21.4 kg, 30 kg) at both altitudes . Physiological parameters such as oxygen consumption, energy expenditure, heart rate, and ventilation were recorded for each breath using a gas analyzer. The rating of perceived exertion was also noted after each load carriage session. Maximal oxygen consumption (VO2max) was measured at sea level and the two high altitudes, and are relative workloads (% of VO2max) were calculated from oxygen consumption. Repeated measure ANOVA was applied to reveal th e significant effects of the independent variables. Results: The participants had observed significant increases in VO2 max with rising altitude. Marked increases in almost all physiological parameters were observed with increasing load, altitude, and speed. at 3.5 km / h at the two high altitudes. Conclusions: Considering the physiological responses, expressions of perceived exertion and changes in relative work load at both of the high altitudes. Indian soldiers are advised to walk slowly with adequate rest in between their schedules and to carry not more than 32% of their body weight.