Published in:
Journal of Applied Physiology, 91 (2001) 4, Seite 1520-1528
Language:
English
DOI:
10.1152/jappl.2001.91.4.1520
ISSN:
8750-7587;
1522-1601
Origination:
Footnote:
Description:
Plasma volume (PV) expansion by endurance training and/or heat acclimatization is known to increase aerobic and thermoregulatory capacities in humans. Also, higher erythrocyte volume (EV) fractions in blood are known to improve these capacities. We tested the hypothesis that training in a hypobaric hypoxic and warm environment would increase peak aerobic power (V˙o 2 peak) and forearm skin vascular conductance (FVC) response to increased esophageal temperature (Tes) more than training in either environment alone, by increasing both PV and EV. Twenty men were divided into four training regimens ( n = 5 each): low-altitude cool (610-m altitude, 20°C ambient temperature, 50% relative humidity), high-altitude cool (2,000 m, 20°C), low-altitude warm (610 m, 30°C), and high-altitude warm (HW; 2,000 m, 30°C). They exercised on a cycle ergometer at 60%V˙o 2 peak for 1 h/day for 10 days in a climate chamber. After training, PV increased in all trials, but EV increased in only high-altitude trials (both P < 0.05). V˙o 2 peak increased in all trials ( P < 0.05) but without any significant differences among trials. FVC response to increased Tes was measured during exercise at 60% of the pretrainingV˙o 2 peak at 610 m and 30°C. After the training, Tes threshold for increasing FVC decreased in warm trials ( P < 0.05) but not in cool trials and was significantly lower in HW than in cool trials ( P < 0.05). The slope of FVC increase/Tes increase increased in all trials ( P < 0.05) except for high-altitude cool ( P > 0.4) and was significantly higher in HW than in cool trials ( P < 0.05). Thus, against our hypothesis, the V˙o 2 peak for HW did not increase more than in other trials. Moreover, slope of FVC increase/Tes increase in HW increased most, despite the similar increase in blood volume, suggesting that factors other than blood volume were involved in the highest FVC response in HW.