Sweating response: a means of evaluating the set-point theory during exercise

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Abstract
Extensive studies were conducted on a normal man and on a paraplegic man at rest and during exercise in constant ambient temperatures of 20, 25, 30 and 35.degree. C. The temperature of external auditory meatus (Tear), mean sentient skin temperature (.hivin.Tsk), sweating rates, O2 uptake and ECG were measured. At rest, when the Tear was raised while the .hivin.Tsk was kept constant, the core (ear) threshold temperature (reference temperature) of sweating was determined for different .hivin.Tsk. In the exercise studies, arm exercise at 40 and 70% of maximum aerobic capacity was performed in separate intervals. At 20.degree. C the sweating response of both subjects was linearly related to the rise in Tear. At higher ambient temperatures a rapid rise in sweating occurred irrespective of the Tear and was followed by a linear sweating versus Tear relationship. During exercise in various environments the reference temperature for the sweating controller was determined by extrapolating the linear portion of the response curve to meet at the abscissa. These reference temperatures were lower than those in the resting studies at corresponding .hivin.Tsk and were also lowered by a rise in the level of exercise. In separate studies .hivin.Tsk was raised at a rate of 0.11.degree. C/min by increasing the ambient temperature from 25 to 45.degree. C. At rest, while the Tear of both subjects was relatively constant, sweating occurred in the normal subject at .hivin.Tsk = 36.7.degree. C, but it did not occur in the paraplegic even when the .hivin.Tsk reached 38.degree. C. During exercise and simultaneous skin heating, however, the paraplegic started sweating even before any appreciable increase in Tear and .hivin.Tsk. Exercise and the exercise level lowered the reference core temperature of sweating in man. This conclusion supports the set-point lowering theory.