Received February 8, 2004
Revised March 30, 2004
Accepted after revision June 2, 2004

¹ Deakin University

^* To whom correspondence should be addressed. E-mail: mharg{at}deakin.edu.au.

	Abstract

Six untrained, male subjects (23 + 1 yrs, 84 + 5 kg, VO2 peak = 3.7 + 0.8 l.min-1) exercised for 60 min at 75 + 1% VO2 peak on seven consecutive days. Muscle samples were obtained prior to commencing cycle exercise training and 24 h after the first and seventh exercise sessions and analysed for citrate synthase activity, glycogen and GLUT-4 mRNA and protein expression. Exercise training increased (P<0.05) citrate synthase by ~20% and muscle glycogen concentration by ~40%. GLUT-4 mRNA levels 24 h after the first and seventh exercise sessions were similar to those measured prior to commencing exercise training. In contrast, GLUT-4 protein expression was increased after 7 d of exercise training (12.4 + 1.5 vs. 3.4 + 1.0 arb. units, P<0.05) and although it tended to be higher 24 after the first exercise session (6.0 + 3.0 vs. 3.4 + 1.0 arb. units), this was not significantly different (P=0.09). These results support the suggestion that the adaptive increase in skeletal muscle GLUT-4 protein expression with short-term exercise training arises from the repeated, transient increases in GLUT-gene transcription following each exercise bout leading to a gradual accumulation of GLUT-4 protein, despite GLUT-4 mRNA returning to basal levels between exercise stimuli.

Key Words: Exercise, Glucose, Skeletal muscle

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