Physiological responses during continuous work in hot dry and hot humid environments in Indians

Studies have been conducted on six young healthy heat acclimatised Indians to determine the physiological changes in prolonged continuous work in thermally neutral and in hot dry and hot humid environments. Physiological responses in maximal efforts i.e. Vo₂ max, V_E max and Cf max were noted. In addition, duration in continuous work at three sub-maximal rate of work in three simulated environments were also noted. Physiological responses like Vo₂, V_E and Cf were noted every 15 minutes of work. Besides these responses, rectal temperature (Tre), mean skin temperature (T_s) and mean sweat rate were also recorded during continuous work.Results indicated a significant decrease in maximum oxygen uptake capacity (Vo₂ max) in heat with no change in maximum exercise ventilation (V_E max) and maximum cardiac frequency. However, the fall in Vo₂ max was more severe in the hot humid environment than in the hot dry climate. Cardiac frequency at fixed oxygen consumption of 1.0, 1.5 and 2.0 l/min was distinctly higher in the hot humid environment than in the hot dry and comfortable temperature. The duration in continuous physical effort in various grades of activities decreased in hot dry environment from that in the-comfortable climate and further decreased significantly in hot humid environment. The highest rate of sweating was observed during work in humid heat. The mean skin temperature (T_s) showed a fall in all the three rates of work in comfortable and hot dry conditions whereas in hot humid environment it showed a linear rise during the progress of work. The rectal temperature on the other hand maintained a near steady state while working at 65 and 82 watts in comfortable and hot dry environments but kept on rising during work in hot humid environment. At the highest work rate of 98 watts, the rectal temperature showed a steady increase even in the hot dry condition. It was thus concluded from the study that a hot humid climate imposes more constraints on the thermoregulatory system during work than in the hot dry condition because of less effective heat dissipation so resulting in reduced tolerance to work.