Metabolic Responses of Indians During Sub-Maximal and Maximal Work in Dry and Humid Heat

Abstract

Studies have been conducted on 10 healthy, naturally heat-acclimated young Indians. Their exercise oxygen consumption (V_{o z}) pulmonary ventilation (V_E) and cardiac frequency (C_t) were measured during submaximal fixed work (600 kgm min⁻¹), as well as graded maximal work on a bicycle ergometer in 5 different environmental conditions—comfortable, very hot with low humidity, very hot with high humidity, extremely hot with low humidity and extremely hot with high humidity. In another Study on 6 of these subjects, total oxygen cost as well as aerobic-anaerobic ratio of oxygen supply during the same fixed work were measured under comfortable and very hot humid conditions. Results indicated a progressive decline in steady state oxygen consumption with increase in the environmental heat load, and a highly significant negative correlation (p> 0·001) between steady state oxygen consumption with the Oxford Index (W.D.). Unlike steady state oxygen, the total oxygen cost of the fixed work did not show any significant change, but there was a significant decrease in the aerobic fraction and increase in the anaerobic fraction of oxygen supply in heat. The C₁ and V_E showed a significantly higher rise during different grades of work in very hot and in extremely hot environments. The V_o, max showed a significant fall in very hot and extremely hot conditions with a greater fall in humid condition than in the dry environment. A highly significant correlation (p<0·001) was obtained between V_o, max and the Oxford Index as well as with wet-bulb temperature.