Thermoregulatory and aerobic changes after endurance training in a hypobaric hypoxic and warm environment

Plasma volume (PV) expansion by endurance training and/or heat acclimatizat ion is known to increase aerobic and thermoregulatory capacities in humans. Also, higher erythrocyte volume (EV) fractions in blood are known to impro ve these capacities. We tested the hypothesis that training in a hypobaric hypoxic and warm environment would increase peak aerobic power ((V) over do t o(2 peak)) and forearm skin vascular conductance (FVC) response to increa sed esophageal temperature (T-es) more than training in either environment alone, by increasing both PV and EV. Twenty men were divided into four trai ning regimens (n = 5 each): low-altitude cool (610-m altitude, 20 degreesC ambient temperature, 50% relative humidity), high-altitude cool (2,000 in, 20 degreesC), low-altitude warm (610 m, 30 degreesC), and high-altitude war m (HW; 2,000 m, 30 degreesC). They exercised on a cycle ergometer at 60% (V ) over dot o(2 peak) for 1 h/day for 10 days in a climate chamber. After tr aining, PV increased in all trials, but EV increased in only high-altitude trials (both P < 0.05). (V) over dot o(2 peak) increased in all trials (P < 0.05) but without any significant differences among trials. FVC response t o increased T-es was measured during exercise at 60% of the pretraining (V) over dot o(2 peak) at 610 rn and 30 degreesC. After the training, T-es thr eshold for increasing FVC decreased in warm trials (P < 0.05) but not in co ol trials and was significantly lower in HW than in cool trials (P < 0.05). The slope of FVC increase/T-es. increase increased in all trials (P < 0.05 ) except for high-altitude cool (P > 0.4) and was significantly higher in H W than in cool trials (P < 0.05). Thus, against our hypothesis, the (V) ove r dot o(2 peak) for HW did not increase more than in other trials. Moreover , slope of FVC increase/T-es increase in HW increased most, despite the sim ilar increase in blood volume, suggesting that factors other than blood vol ume were involved in the highest FVC response in HW.