Decreased glucose turnover following short-term training is
unaccompanied by changes in muscle oxidative potential.
Phillips, S. M., H. J. Green, M. A. Tarnopolsky, and S. M. Grant.
Department of Kinesiology, University of Waterloo, Waterloo, ON,
Canada N2L 3G1 and Department of Kinesiology, McMaster University,
Hamilton, ON, Canada L8N 3Z5
APStracts 2:0055E, 1995.
This study investigated the hypothesis that training induced
reductions in exercise blood glucose utilization can occur
independently of increases in muscle mitochondrial potential. To
induce a training adaptation, eight active participants (23+/-1 yr,
80.6+/-3.7 kg, mean+/-SE) with a maximal oxygen consumption (O2max)
of 45.5+/-2.4 ml/kg/min, cycled at 59% O2 max for 2h per day for 10
consecutive days. Measurements of blood glucose appearance (Ra) and
disappearance (Rd), using a primed continuous infusion of [6,6
-2H2]glucose, were made during 90 min of cycle exercise (59% O2max)
performance prior to (Pre) and following (Post) training. Training
resulted in a 25% decrease (P<0.01) in mean glucose Ra during
exercise (43.0+/-3.7 to 34.4+/-2.8 [mu]mol/kg/min). Since blood
glucose concentration was not different between training conditions,
glucose metabolic clearance rate was also depressed (P<0.05).
Exercise induced glycogen depletion in vastus lateralis muscle was
reduced (P<0.05) with training. Calculation of carbohydrate and fat
oxidation based on the respiratory exchange ratio supported a shift
towards greater preference for fat. Since training did not elicit
changes in the maximal activities of citrate synthase and malate
dehydrogenase, two enzymes of the citric acid cycle, it would appear
that increases in mitochondrial potential are not necessary for the
adaptations that occurred.
Received 23 September 1994; accepted in final form 24 March 1995.
APS Manuscript Number E393-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 4 April 1995.