Progressive effect of endurance training on metabolic adaptations
in working skeletal muscle.
Phillips, S. M., H. J. Green, M. A. Tarnopolsky, G. J. F.
Heigenhauser, and S. M. Grant.
Dept. of Kinesiology, University of Waterloo, Waterloo, ON, N2L 3G1
and Dept. of Kinesiology and Cardiorespiratory Medicine, McMaster
University, Hamilton, ON, L8N 3Z5
APStracts 2:0225E, 1995.
We investigated the hypothesis that a program of prolonged endurance
training, previously shown to decrease metabolic perturbations to
acute exercise within 5 days of training would result in greater
metabolic adaptations following a longer training duration. Seven
healthy male volunteers (O2=3.52+/-0.20 l/min; mean+/-SE) engaged in
a training program, consisting of 2h of cycle exercise at 59% of pre
-training O2 peak 5-6 times/wk. Responses to a 90 min submaximal
exercise challenge were assessed pre-training (PRE), after 5 days
(5D) and 31 days (31D) of training. Based on biopsies obtained from
the vastus lateralis muscle, it was found that following 5D of
training, muscle lactate concentration, phosphocreatine (PCr)
hydrolysis, and glycogen depletion were reduced versus PRE (all
P<0.01). Further training (26 days) showed that at 31D the
reduction in PCr, and the accumulation of muscle lactate was even
less than at 5D (P<0.01). Muscle oxidative potential, estimated
from the maximal activity of succinate dehydrogenase (SDH), was
increased only following 31D of training (+41%; P<0.01). In
addition, O2 peak was only increased (10%) by 31D (P<0.05). The
results show that a period of short-term training results in many
characteristic training adaptations, but that these adaptations
occurred prior to increases in mitochondrial potential. However, a
further period of training resulted in further adaptations in muscle
metabolism and muscle phosphorylation potential, which were linked to
the increase in muscle mitochondrial capacity.
Received 1 May 1995; accepted in final form 7 September 1995.
APS Manuscript Number E197-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95