Effect of hypohydration on hyperthermic hyperpnea and cutaneous vasodilation during exercise in men

hypohydration on hyperthermic hyperpnea and cutaneous vasodilation dur-ing exercise in men. J Appl Physiol 105: 1509–1518, 2008. First published September 11, 2008; doi:10.1152/japplphysiol.01206.2007.—We tested the hypothesis that, in humans, hypohydration attenuates hyperthermic hyperpnea during exercise in the heat. On two separate occasions, thirteen male subjects performed a fluid replacement (FR) and a no-fluid replacement (NFR) trial in random order. The subjects performed two bouts of cycle exercise (Ex1 and Ex2, 30–60 min) at 50 % peak oxygen uptake (V ˙ O2 peak) in 35°C separated by a 70- to 80-min rest period, during which they drank water containing 25 mosmol/l sodium in the FR trial but not the NFR trial. The drinking in the FR trial nearly restored the body fluid to the euhydrated condition, so that the body fluid status differed between the trials before Ex2 (the difference in plasma osmolality before Ex2 was 9.4 mosmol/kgH2O; plasma volume was 7.6%, and body weight wa