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| Abstract |
he purpose of this study was to determine whether or not a gradual reduction in ambient temperature affected core temperature or physiological and hormonal responses during prolonged exercise in a neu...tral thermal condition. On two occasions, in random order and separated by 1 week, six male distance runners [mean age: 20 ± 1 years; maximal oxygen uptake (VO_2max: 63.8 ± 5.0 ml/kg/min); mean ± SD] exercised for 60 min on a cycle ergometer at 67%VO_2max in an environmental chamber, on one occasion at a gradually lowered ambient temperature (DEC-T: ambient temperature lowered during exercise by 0.3°C every 3 min from 23°C at rest) and another occasion at a constant ambient temperature of 23 ± 0.2°C (CONT). Subjects were given 100 ml of water every 15 min during exercise. Rectal temperature and heart rate were recorded continuously throughout the entire test period. Expired gas samples were collected for 10 min before exercise, for the last 5 min of every 10 min during exercise, and at 30 min and 60 min after exercise. Blood samples were collected before exercise, at 10 min intervals during exercise, and 30 min and 60 min after exercise. Exercise intensity was similar for both trials (DEC-T: 67.9 ± 2.9%VO_2max, CONT: 67.3 ± 3.0% VO_2max). Ambient temperature on the DEC-T trial was significantly lower than that of the CONT trial after 17 min of exercise (p<0.05), and reached 17.9 ± 1.6 °C at the end of exercise (CONT trial: 23.0 ± 1.1 °C, p<O.O1). Rectal temperature was not significantly different for the trials at pre-exercise, during exercise and recovery (at end of exercise; DEC-T: 38.98 ± 0.48°C, CONT: 39.20 ± 0.28°C). Body mass losses showed no significant differences between trials (DEC-T: -1.2 ± 0.4 kg, CONT: -1.2 ± 0.3 kg). Whole-period minute ventilation, heart rate and respiratory exchange ratio also showed no significant differences between the two test periods. Concentrations of plasma-free and sulpho-conjugated catecholamines, serum cortisol, growth hormone, glycerol and free fatty acid, and blood lactate were similar for both trials at all sampling points. These results show that a gradual reduction of ambient temperature of about 5°C does not influence core temperature or physiological and hormonal responses during prolonged exercise. Additionally, these data suggest that physiological and hormonal responses during prolonged exercise might be strongly influenced by core temperature.show more
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