Abstract

In an effort to ascertain the contribution of elevated core temperature on the plasma catecholamines (Ca) response to prolonged exercise four trained men were studied under two thermal conditions during 45 min of bicycle exercise and during passive heating. On one testing day each subject was heat-stressed during exercise wearing a nylon pullover shell and cotton pants, (heat stress treatment); on the second day fans were directed on the subjects exercising in a thermoneutral environment (fan treatment). The passive heating experiment was conducted in a hot water bath (41 degrees C). The exercise heat stress treatment produced a higher plasma norepinephrine (NE) concentration in all subjects than the fan treatment. A rise in rectal temperature (Tre) during passive heating resulted in quantitatively small changes in plasma E and NE. The heat load combined with the exercise task produced an increase in plasma NE concentration greater than the sum of the values measured during exercise in the thermoneutral environment and passive heating. This suggested that the combination of stressors caused an augmentation of the sympathetic nervous systems response. Finally, the added heat load caused changes in plasma NE and little change in plasma E, suggesting a differential Ca response with heat stress. Verf.-Referat