Effects of environmental heart on performance and some physiological responses of a man during a psychomotor task

In climatic chamber experiments some physiological responses of a young healthy man were studied. He was able to perform a pursuitmeter task in a fairly wide range of warm climates without decrement of performance. The highly trained and heat-acclimatized subject was exposed nearly undressed to various ambient temperatures (28--55 degrees C) and air humidities (10--92%) which were combined in such a way that the conditions were tolerable up to 4 h. In 18 experiments the man was sitting quietly all the time, and in a parallel series of 19 experiments (up to 50 degrees C) he performed the pursuitmeter task during the last 2 hours of each exposure. Under equal climatic conditions work caused a slight increase in oxygen uptake corresponding to an increase in metabolic heat generation by about 70 kj/h (17kcal/h) on the average. Rectal temperature and temperature next to the eardrum were 0.1--0.2 degrees C higher at work as compared with rest. Weight loss at work exceeded weight loss at rest, the difference ocrresponding to an increase in evaporative heat loss by about 110 kj/h (26 kcal/h) which resulted in a decrease of mean skin temperature of 0.5 to 0.9 degrees C. Superelevation of heart rate due to work reached about 10 beats/min in a thermally neutral environment, but up to 30 beats/min in hot dry and warm humid surrounding, reflecting the additional effort for maintaining performance under conditions of increasing heat stress.