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1 School of Medical Sciences, RMIT University, Melbourne, Victoria, Australia
2 School of Medical Sciences, RMIT University, Melbourne, Victoria, Australia; Melbourne, Victoria, Australia
3 School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Victoria, Australia
* To whom correspondence should be addressed. E-mail: john.hawley{at}rmit.edu.au.
To determine whether pre-exercise muscle glycogen content influences the transcription of several early response genes involved in the regulation of muscle growth, 7 male strength-trained subjects performed one-legged cycling exercise to exhaustion to lower muscle glycogen levels in one leg (LOW) and the following day completed a unilateral bout of resistance training (RT). Muscle biopsies from both legs were taken at rest, immediately post RT and after 3 h of recovery. Resting glycogen content was higher in the control leg (NORM) than LOW (435 ±87 vs. 193 ±29 mmol.kg-1d.w., P<0.01). RT decreased glycogen content in both legs (P<0.05), but post-exercise values remained significantly higher in NORM than LOW (312 ±129 vs. 102 ±34 mmol.kg-1d.w., P<0.01). GLUT4 (3-fold; P<0.01) and Glycogenin mRNA abundance (2.5-fold; NS) were elevated at rest in NORM but such differences were abolished after exercise. Pre-exercise mRNA abundance of atrogenes was also higher in NORM compared to LOW (Atrogin, ~14-fold P<0.01; MuRF ~3-fold P<0.05) but decreased for Atrogin in NORM following RT (P<0.05). There were no differences in the mRNA abundance of myogenic regulatory factors and IGF-1 in NORM compared to LOW. Our results demonstrate that i) low muscle glycogen content has variable effects on the basal transcription of select metabolic and myogenic genes at rest, and ii) any differences in basal transcription are completely abolished after a single bout of heavy resistance training. We conclude that commencing resistance exercise with low muscle glycogen does not enhance the activity of genes implicated in promoting hypertrophy.
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