Hyperhydration: tolerance and cardiovascular effects during
uncompensable exercise-heat stress.
Latzka, William A., Michael N. Sawka, Scott J. Montain, Gary S.
Skrinar, Roger A. Fielding, Ralph P. Matott, and Kent B. Pandolf.
U.S. Army Research Institute of Environmental Medicine, Natick, MA
01760-5007, Boston University, Boston, MA 02215
APStracts 5:0048A, 1998.
This study examined the efficacy of glycerol and water hyperhydration
(one hour before exercise) on tolerance and cardiovascular strain
during uncompensable exercise-heat stress (UCHS). The approach was to
determine if 1-h pre-exercise hyperhydration (29.1 ml of water/kg LBM
with or without glycerol 1.2 g/kg LBM) provided a physiologic
advantage over euhydration. Eight heat-acclimated men completed three
trials (control euhydration before exercise, glycerol and water
hyperhydration) consisting of treadmill exercise-heat stress
(Ereq/Emax =415%). During exercise (55% O2 max), there was no
difference between glycerol or water hyperhydration method for
increasing (P<0.05) total body water. Endurance was longer
(P<0.05) for glycerol hyperhydration (33.8 +/-3.0 min) than control
(29.5 +/-3.5 min), but not different (P>0.05) from water
hyperhydration (31.3 +/-3.1 min). Hyperhydration did not alter
(P>0.05) core temperature, whole body sweating rate, cardiac
output, blood pressure, total peripheral resistance or core
temperature tolerance. Exhaustion from heat strain occurred at
similar core temperatures, skin temperatures, and heart rates in each
trial. Symptoms at exhaustion included syncope/ataxia (n=11), fatigue
(n=10), dyspnea (n=2), and muscle cramps (n=1). It is concluded that
1-h pre-exercise glycerol hyperhydration provides no meaningful
physiologic advantage over water hyperhydration and that
hyperhydration per se only provides the advantage (over euhydration)
of delaying hypohydration during UCHS.
Received 9 April 1997; accepted in final form 29 January 1998.
APS Manuscript Number A338-7.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 19 February 1998