A reduced lactate mass explains much of the glycogen sparing
associated with training.
Crowley, Michael A., Wayne T. Willis, Kathleen S. Matt, and Casey M.
Donovan.
Arizona State University, Tempe, Arizona, University of Southern
California
APStracts 3:0114A, 1996.
Endurance training is associated with glycogen (GLY) sparing,
generally attributed to less carbohydrate (CHO) oxidation. However,
untrained individuals commit a greater fraction of CHO to lactate
(LA) accounting for a portion of the GLY 'spared'. We examined the
effects of training (running 1h/day at 30 m/min up an 8 degrees
grade) on whole body CHO distribution and oxidation. Female Long
Evans Rats (n=16) were assigned to control (UNTR) and trained (TR)
groups. Two days before the experiment, animals were chronically
catheterized. On the day of the experiment, animals ran for 20 min at
a speed of 28 m/min. Animals were sacrificed with an overdose
pentobarbital injection via the catheter while running. Whole
carcasses were then promptly freeze-clamped with a liquid N2 cooled
press. Whole body carcass powder was assayed for LA, GLY and glucose
(GLU). Resting whole body values were not different between groups
(LA = 0.78+/-0.06 vs. 0.83+/-0.07, GLY = 4.46+/-0.62 vs. 3.77+/-0.35,
GLU = 0.19+/-0.07 vs. 0.23+/-0.09 mmoles /body for TR and UNTR
respectively). However, post-exercise LA was higher in UNTR vs TR
(2.01+/-0.28 vs 1.13+/-0.09 mmoles / body) and GLY was lower in the
UNTR vs TR (1.58+/-0.25 vs 3.42+/-0.43 mmoles / body). Likewise UNTR
animals displayed higher epinephrine levels than TR at the end of the
exercise bout (4.9+/-1.0 vs 1.7+/-0.4 ng/ml). Differences between
groups in LA and GLU masses (post-exercise minus rest data) accounted
for 60% of the GLY differences. GLY spared from oxidation and
replaced by increased fat oxidation only accounted for 40% of the
differences in GLY levels between trained and untrained animals in
this experimental design. We conclude that untrained mammals commit a
significant portion of their carbohydrate pool to lactate which
accounts for almost half of the apparent glycogen spared during
moderate intensity exercise in the trained state.
Received 10 September 1995; accepted in final form 13 February
1996.
APS Manuscript Number A996-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96