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Department of Sports Medicine, Research Center on Aging and Adaptation, Shinshu University School of Medicine, Matsumoto 390-8621, Japan
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 (
O2 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%
O2 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). O2 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 pretraining
O2 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 O2 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.
endurance training; altitude; skin blood flow; aerobic power; blood volume; humans
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