Physiological responses during work in hot humid environments.

Studies have been conducted on 6 young healthy Indians in simulated comfortable, hot humid and very hot humid conditions to evaluate the physiological reactions during work. Physiological responses like exercise oxygen consumption (VO2), pulmonary ventilation (VE) and heart rate (HR) were noted during sub-maximal fixed work rates of 400, 500 and 600 kgM/min. In addition, duration of continuous work at these three rates of work, in the three simulated environments was also noted. Physiological responses i.e. VO2, VE and HR were noted every 15 minutes of work. Besides these responses, rectal temperature (Tr), mean skin temperature (Ts) and mean sweat rate were also noted during the continuous work. Results indicated a significantly higher oxygen cost (VO2) during 400 kgM/min of work in hot and very hot humid environments whereas, in the higher rates of work, the changes were not significant. The cardiac frequency showed a significantly higher rise during different grades of activities in hot and very hot environments except in the highest work rate in hotter environments, possibly due to attainment of maximum heart rate. The duration of continuous physical efforts in various grades of activities decreased significantly (P less than 0.001) in hot humid environments than in the comfortable temperature. During the progression of the work, the mean skin temperature decreased in comfortable temperature but increased in hot humid environments. The mean rectal temperature, increased during work in hot humid environment, and the rate of rise was much faster in higher work rates attaining the target temperature much earlier. The rate of sweating increased significantly as the heat load of the body increased. In hot humid environments, work performance decreased due to early attainment of maximum heart rate, reduction in VO2 max, disproportionate rise in rectal temperature, narrowing of the difference between the core and the skin temperature and attainment of maximum sweating rate.

Endurance capacity for continuous effort in terms of aerobic and anaerobic fraction of oxygen supply.

Studies have been conducted on 13 young healthy adults of average fitness on endurance work of varying durations lasting for 2-31 minutes using bicycle ergometer. Aerobic-anaerobic fractions of oxygen supply during each effort was determined. The data from Astrand and Rodahl on aerobic O2--supply and duration in maximal efforts from 1-120 minutes on a highly trained subject have also been considered. The plot of log endurance time against log (aerobic/anaerobic ratio) exhibits a slight departure from linearity, indicating independent contributions from aerobic and anaerobic fractions of oxygen supply. An equation was derived of the form: T - Au1k1u2--k2 where u1 end u2 are the aerobic and anaerobic fractions respectively which has been found to yield highly significant correlation coefficient between log-estimated and log-observed endurance time (0.9996 for Astrand and Rodahl's data on a single subject and 0.9640 for the present data on 13 subjects). This index is, therefore, quite suitable for the assessment of endurance capacity in terms of a single physiological parameter, and is likely to be superior to indices in current use.

Body temperature and basal metabolic changes during acclimatization to altitude (3,500 m) in man.

Oral temperature (Tor), mean weighted skin temperature (Ts), mean body temperature (Tb) and basal oxygen consumption were studied on twelve young men at sea level. Then they were flown to an altitude of 3,500 m and the readings were continued after 24 hours of their arrival and thereafter at four day intervals for a period of 25 days. Thereafter the subjects were flown back and retested at sea level. Oxygen consumption was recorded at weekly intervals only. The changes in body temperature were compared with those of their basal oxygen consumption. The results indicate that there is a slight rise in the Tor on arrival at altitude and thereafter a gradual fall. A steady and continuous fall was recorded in Ts and Tb throughout the stay at altitude. The basal oxygen consumption showed an initial rise which has come back to normal by the third week of their stay at altitude. On retest, the valves of body temperature and oxygen consumption reached their own initial sea-level pattern. The observation suggests that central mechanisms are involved in bringing about a fall in body temperature during altitude acclimatization.