Hypohydration effects on skeletal muscle performance and
metabolism: a 31p mrs study.
Montain, Scott J., Sinclair A. Smith, Ralph P. Mattot, Gary P.
Zientara, Ferenc A. Jolesz, and Michael N. Sawka.
U.S. Army Research Institute of Environmental Medicine, Natick, MA.
Boston University, Boston, MA 01760. Brigham and Women's Hospital and
Harvard Medical School, Boston, MA 02115
APStracts 5:0062A, 1998.
The purpose of this study was to determine if hypohydration reduces
skeletal muscle endurance and whether increased H+ and Pi might
contribute to performance degradation. Ten physically active
volunteers (age 21-40 y) performed supine single-leg knee extension
exercise to exhaustion in a 1.5 Tesla whole body magnetic resonance
spectroscopy (MRS) system when euhydrated and when hypohydrated (4%
body weight). 31P spectra were collected at a rate of one per second
at rest, exercise and recovery, grouped and averaged to represent 10
second intervals. The desired hydration level was achieved by
performing 2-3 h exercise in a warm room (40 degrees C db, 20% rh)
with or without fluid replacement 3-8 h prior to the experiment. Time
to fatigue was reduced (P<0.05) 15% when hypohydrated (213+/-12 vs
251+/-15 sec; +/-se). Muscle strength was generally not affected by
hypohydration. Muscle pH and Pi/[beta]-ATP were similar during
exercise and at exhaustion regardless of hydration state. The time
constants for PCr recovery were also similar between trials. In
summary, moderate hypohydration reduces muscle endurance and neither
H+ nor Pi concentration appear to be related to these reductions.
Received 18 July 1997; accepted in final form 11 February 1998.
APS Manuscript Number A660-7.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 19 February 1998