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Received March 2, 2006
Revised March 16, 2006
Accepted after revision April 2, 2006
2AMPK activation and lower energy charge and fat oxidation in men than in women during submaximal exercise
1 The Copenhagen Muscle Research Centre
* To whom correspondence should be addressed. E-mail: croepstorff{at}ifi.ku.dk.
5'AMP-activated protein kinase (AMPK) is an energy sensor activated by perturbed cellular energy status such as during muscle contraction. Activated AMPK is thought to regulate several key metabolic pathways. We used gender comparison to investigate whether AMPK signalling in skeletal muscle regulates fat oxidation during exercise. Moderately trained women and men completed 90 min bicycle exercise at 60% VO2 peak. Both AMPK Thr172 phosphorylation and 
2AMPK activity increased by exercise in men (~200%, p<0.001) but not significantly in women. The gender difference in muscle AMPK activation with exercise was accompanied by an increase in muscle free AMP (~164%, p<0.01), free AMP/ATP ratio (159%, p<0.05), and creatine (~42%, p<0.001) in men but not in women (NS), suggesting that lack of AMPK activation in women was due to better maintenance of muscle cellular energy balance compared with men. During exercise, fat oxidation per kg lean body mass was higher in women than in men (p<0.05). Regression analysis revealed that a higher proportion of type 1 muscle fibres (~23%, p<0.01) and a higher capillarization (~23%, p<0.05) in women than in men could partly explain the gender difference in 2AMPK activity (r=-0.54, p<0.05) and fat oxidation (r=0.64, p<0.05) during exercise. On the other hand, fat oxidation appeared not to be regulated via AMPK. In conclusion, during prolonged submaximal exercise at 60% VO2 peak, higher fat oxidation in women cannot be explained by higher AMPK signalling but is accompanied by improved muscle cellular energy balance in women probably due to gender specific muscle morphology.
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