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1 Biomedical Kinesiology, University of Leuven, Heverlee (Leuven), Belgium
2 Department of Movement and Sport Sciences, University Ghent, Ghent, Belgium; Department of Biomedical Kinesiology, FaBeR - K.U.Leuven, Leuven, Belgium
3 Department of Biomedical Kinesiology, FaBeR - K.U.Leuven, Leuven, Belgium
4 Movement Sciences, Maastricht University, Maastricht, Netherlands
5 Dept. of Human Physiology, University of Copenhagen, Copenhagen, Denmark
6 Human Biology, Maastricht University, Maastricht, Netherlands
7 Department of Human Biology, University of Guelph, Guelph, Canada
8 Copenhagen Muscle Research Centre, Dept. of Human Physiology, University of Copenhagen, Copenhagen, Denmark
* To whom correspondence should be addressed. E-mail: peter.hespel{at}faber.kuleuven.be.
Skeletal muscle gene response to exercise depends on nutritional status during and after exercise, but it's unknown whether muscle adaptations to endurance training are affected by nutritional status during training sessions. Therefore, this study investigated the effect of an endurance training program (6wk, 3d/week, 1-2h, 75% of peak VO2) in moderately active males. They trained in the fasted (F; n=10) or carbohydrate-fed state (CHO; n=10) while receiving a standardized diet (65%En from carbohydrates, 20%En fat, 15%En protein). Before and after the training period, substrate use during a 2h exercise bout was determined. During these experimental sessions, all subjects were in a fed condition and received extra carbohydrates (1g·kg-1 bw·h-1). Peak VO2 (+7%), succinate dehydrogenase activity, GLUT4, and hexokinase II content were similarly increased between F and CHO. Fatty acid binding protein (FABPm) content increased significantly in F (p=.007). Intramyocellular triglyceride content (IMCL) remained unchanged in both groups. After training, pre-exercise glycogen content was higher in CHO (545±19mmol·kg-1 dw; p=.02), but not in F (434±32mmol·kg-1 dw; p=.23). For a given initial glycogen content, F blunted exercise-induced glycogen breakdown when compared with CHO (p=.04). Neither IMCL breakdown (p=.23) nor fat oxidation rates during exercise were altered by training. Thus, short-term training elicits similar adaptations in peak VO2 whether carried out in the fasted or carbohydrate fed state. Although there was a decrease in exercise-induced glycogen breakdown and an increase in proteins involved in fat handling after fasting training, fat oxidation during exercise with carbohydrate intake was not changed.
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