AJP - Endocrinology and Metabolism, Vol 270, Issue 3 E456-E462, Copyright © 1996 by American Physiological Society
Increments in skeletal muscle GLUT-1 and GLUT-4 after endurance training in humans
S. M. Phillips, X. X. Han, H. J. Green and A. Bonen
Department of Kinesiology, University of Waterloo, Ontario, Canada.
We investigated the time course of training-induced changes in the
expression of GLUT-1 and GLUT-4 in human skeletal muscle. Seven healthy
males trained for 2 h/day (approximately 60% pretraining VO2peak) for 31
days (31D). Muscle biopsies were obtained before training (PRE) and after 5
(5D) and 31 days (31D) of training. Training resulted in progressive
increases in muscle GLUT-4 with increasing training duration
(PRE<5D<31D; P<0.01). Muscle GLUT-1 content was also increased
(P<0.05) after training; however, the increase was not observed until
31D (131%). Increases in muscle hexokinase (HK) activity were complete by
5D (P<0.01). Muscle malate dehydrogenase activity was not elevated after
5D of training but was increased (+35%; P<0.01) at 31D. Results from
this study show that increases in both GLUT-4 and HK represent early
training-induced adaptations to prolonged exercise training. As training
progresses, further increases in GLUT-4, but not HK, occur in conjunction
with an increase in muscle mitochondrial potential and GLUT-1.
