title: Effects of hypohydration on thermoregulation during exercise before and after 5-day aerobic training in a warm environment in young men.
abstract: We examined whether enhanced cardiovascular and thermoregulatory responses during exercise after short-term aerobic training in a warm environment were reversed when plasma volume (PV) expansion was reversed by acute isotonic hypohydration. Seven young men performed aerobic training at the 70% peak oxygen consumption rate (Vo(₂peak)) at 30°C atmospheric temperature and 50% relative humidity, 30 min/day for 5 days. Before and after training, we performed the thermoregulatory response test while measuring esophageal temperature (T(es)), forearm skin vascular conductance, sweat rate (SR), and PV during 30 min exercise at the metabolic rate equivalent to pretraining 65% Vo(₂peak) in euhydration under the same environment as during training in four trials (euhydration and hypohydration, respectively). Hypohydration targeting 3% body mass was attained by combined treatment with low-salt meals to subjects from ~48 h before the test and administration of a diuretic ~4 h before the test. After training, the T(es) thresholds for cutaneous vasodilation and sweating decreased by 0.3 and 0.2°C (P = 0.008 and 0.012, respectively) when PV increased by ~10%. When PV before and after training was reduced to a similar level, ~10% reduction from that in euhydration before training, the training-induced reduction in the threshold for cutaneous vasodilation increased to a level similar to hypohydration before training (P = 0.093) while that for sweating remained significantly lower than that before training (P = 0.004). Thus the enhanced cutaneous vasodilation response after aerobic training in a warm environment was reversed when PV expansion was reversed while the enhanced SR response remained partially.
authors.affiliation: Dept. of Sports Medical Sciences, Institute on Aging and Adaptation, Shinshu Univ. Graduate School of Medicine, Japan. nosehir@shinshu-u.ac.jp
authors.forename: Shigeki
authors.initials: S
authors.lastname: Ikegawa
authors.forename: Yoshi-Ichiro
authors.initials: Y
authors.lastname: Kamijo
authors.forename: Kazunobu
authors.initials: K
authors.lastname: Okazaki
authors.forename: Shizue
authors.initials: S
authors.lastname: Masuki
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Okada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nose
mesh_terms: D000704:Analysis of Variance; D017704:Baroreflex / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005542:Forearm / Q000098:blood supply; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology; D010953:Plasma Volume / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D013546:Sweating