Comfort and thermal sensations and associated physiological responses during exercise at various ambient temperatures

Abstract

Sensory estimates, using nominal scales, were made by four healthy male subjects dressed in shorts, while pedalling a bicycle ergometer (50 rpm) at 25%, 50%, and 75% maximal oxygen uptake and at 10°, 20°, and 30° ambient air temperature (RH 40%). Parallel physiological measurements were rectal, muscle (quadriceps), and average skin temperature, metabolism, sweat heat loss from the skin, and skin heat conductance (a measure of skin blood flow). Conclusions: After 30–40 minutes of steady exercise (1) temperature sensations ranging from “cool” to “hot” are principally related to skin and ambient air temperatures and unrelated to metabolic rate, muscle, and rectal temperatures; (2) warm discomfort is principally related to skin sweating and skin conductance and is affected either by air temperature and metabolism or by both skin and rectal temperature. It thus appears that during steady state exercise the judgement of temperature is dominated by sensor mechanisms in the skin and that warm discomfort is principally governed by thermoregulatory effector mechanisms (sweating and skin blood flow). During thermal transients caused by the rise in metabolic energy with the start of exercise both comfort and temperature sensation are related to the initial rise in mean body temperature. After 20–30 minutes of exercise the conclusions above apply. Using metabolic rate and the ambient temperature as the parameters, a zone of comfort (i.e., zero discomfort) has been described for steady exercise. The lower boundary of this zone is described by those exercise levels and air temperatures in which skin sweat is zero. The upper boundary corresponds to a skin sweat rate equivalent to evaporative heat loss of 150 kcal/m 2-hour or approximately 65% wettedness of the skin. For this upper limit considerable individual variability can be expected. Finally, in this zone the percentage of maximal oxygen uptake should not exceed 50%.