M. Hargreaves et al., EFFECT OF FLUID INGESTION ON MUSCLE METABOLISM DURING PROLONGED EXERCISE, Journal of applied physiology, 80(1), 1996, pp. 363-366
Five trained men were studied during 2 h of cycling exercise at 67% pe
ak oxygen uptake at 20-22 degrees C to examine the effect of fluid ing
estion on muscle metabolism. On one occasion, the subjects completed t
his exercise without fluid ingestion (NF) while on the other they inge
sted a volume of distilled deionized water that prevented loss of body
mass (FR). No differences in oxygen uptake during exercise were obser
ved between the two trials. Heart rate was lower (P < 0.01) throughout
exercise when fluid was ingested, and rectal temperature after 2 h of
exercise was lower (38.0 +/- 0.2 and 38.6 +/- 0.2 degrees C for FR an
d NF, respectively; P < 0.01), as was muscle (vastus lateralis) temper
ature (38.5 +/- 0.4 and 39.1 +/- 0.5 degrees C for FR and NF, respecti
vely; P < 0.05). Resting muscle ATP, creatine phosphate, creatine, gly
cogen, and lactate levels were similar in the two trials, as were the
postexercise ATP, creatine phosphate, and creatine levels. In contrast
, muscle glycogen was higher (P < 0.05) and muscle lactate was lower (
P < 0.05) after 2 h of exercise in FR compared with NF. Net muscle gly
cogen utilization during exercise was reduced by 16% when fluid was in
gested (318 +/- 46 and 380 +/- 53 mmol/kg dry weight for FR and NF, re
spectively; P < 0.05). These results indicate that fluid ingestion red
uces muscle glycogen use during prolonged exercise, which may account,
in part, for the improved performance previously observed with fluid
ingestion.