Volume repletion following exercise-induced volume depletion in
man: replacement of water and sodium losses.
Maughan, Susan M Shirreffs Ronald J.
University Medical School, Foresterhill, Aberdeen AB25 2ZD,
Scotland
APStracts 5:0003F, 1998.
Sodium and water loss during, and replacement following, exercise
-induced volume depletion was investigated in six volunteers volume
depleted by 1.89 (0.17) % [mean (S.D.)] of body mass by intermittent
exercise in a warm, humid environment. Exercise was in an large, open
plastic bag allowing collection of all sweat secreted during
exercise. Over 60 min beginning 40 min after the end of exercise,
subjects ingested drinks containing 0, 25, 50 or 100 mmol l-1 Na+ in
a volume (ml) equivalent to 150% of the mass lost (g) by volume
depletion. Body mass loss and sweat electrolyte (Na+, K+, Cl-) loss
were the same on each trial. The measured sweat Na+ concentration was
49.2 (18.5) mmol l-1, and the total loss [63.9 (38.7) mmol] was
greater than that ingested on Trials 0 and 25. Urine production over
the 6 h recovery period was inversely related to the amount of sodium
ingested. Subjects were in whole body negative sodium balance on
Trials 0 [-104 (48) mmol] and 25 [-65 (30) mmol], were essentially in
balance on Trial 50 [-13 (29) mmol], but were in positive sodium
balance on Trial 100 [75 (40) mmol]. Only on Trial 100 were subjects
in positive fluid balance at the end of the study. There was a large
urinary loss of potassium over the recovery period on Trial 100,
despite a negligible intake during volume repletion. These results
confirm the importance of replacement of sodium as well as water for
volume repletion following sweat loss. The sodium intake on Trial 100
was appropriate for acute fluid balance restoration, but its
consequences on potassium levels must be considered to be undesirable
in terms of whole body electrolyte homeostasis for anything other
than the short term.
Received 25 April 1997; accepted in final form 2 January 1998.
APS Manuscript Number F140-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 9 January 1998