Mj. Buono et Aj. Wall, Effect of hypohydration on core temperature during exercise in temperate and hot environments, PFLUG ARCH, 440(3), 2000, pp. 476-480
The purpose of this study was to compare directly the physiological consequ
ences of 5% hypohydration or euhydration during exercise in both temperate
(23 degrees C) and hot (33 degrees C) environments. The subjects were eight
male volunteers. Each performed four 1-h exercise bouts at 60% maximum oxy
gen uptake, one in each of the following conditions: hot-hypohydrated, hot-
euhydrated, temperate-hypohydrated, and temperate-euhydrated. Heart rate (H
R), rectal temperature (T-re), forearm blood flow, and oxygen uptake were m
easured after 20, 40, and 60 min exercise. Whole-body sweat rate was also d
eter mined for each exercise bout. Hypohydration increased T-re significant
ly (P<0.05) more in the hot environment (0.16 degrees C per 1% decrease in
body mass) than in the temperate environment (0.08 degrees C per 1% hypohyd
ration). Furthermore, compared with euhydration, hypohydration decreased fo
rearm blood flow and whole-body sweat rate significantly more during exerci
se in the hot than in the temperate environment. The reductions in forearm
blood flow and whole-body sweat rate appear to have decreased heat loss, th
us accounting for the increase in T-re during exercise in the heat while hy
pohydrated. In conclusion, this study illustrates that the physiological co
nsequences of hypohydration during exercise are exacerbated in the heat.