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Am J Physiol Endocrinol Metab (November 1, 2005). doi:10.1152/ajpendo.00464.2005
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Submitted on September 23, 2005
Accepted on October 26, 2005

Effect of exercise intensity and hypoxia on skeletal muscle AMPK signaling and substrate metabolism in humans

G D Wadley1, R S Lee-Young1, B J Canny2, C Wasuntarawat3, Z-P Chen4, M Hargreaves1, B E Kemp4, and G K McConell1*

1 Department of Physiology, The University of Melbourne, Parkville, Victoria, Australia
2 Department of Physiology, Monash University, Clayton, Victoria, Australia
3 Naresuan University, Thailand
4 Department of Physiology, St. Vincents Institute and CSIRO Molecular and Health Sciences, Fitzroy, Victoria, Australia

* To whom correspondence should be addressed. E-mail: mcconell{at}unimelb.edu.au.

We compared in human skeletal muscle the effect of absolute versus relative exercise intensity on AMP-activated protein kinase (AMPK) signaling and substrate metabolism under normoxic and hypoxic conditions. Eight untrained males cycled for 30 min under hypoxic conditions (11.5% O2, 111 ± 12 watts, 72 ± 3% hypoxia VO2peak; 72% Hypoxia) or under normoxic conditions (20.9% O2) matched to the same absolute (111 ± 12 watts, 51 ± 1% normoxia VO2peak; 51% Normoxia) or relative (to VO2peak) intensity (171 ± 18 watts, 73 ± 1% normoxia VO2peak; 73% Normoxia). Increases (p<0.05) in AMPK activity, AMPK{alpha} Thr172 phosphorylation, ACC{beta} Ser221 phosphorylation, free AMP content and glucose clearance were more influenced by the absolute rather than the relative exercise intensity, being greatest in 73% Normoxia with no difference between 51% Normoxia and 72% Hypoxia. In contrast to this, increases in muscle glycogen use, muscle lactate content and plasma catecholamine concentration were more influenced by the relative than the absolute exercise intensity, being similar in 72% Hypoxia and 73% Normoxia, with both trials higher than in 51% Normoxia. In conclusion, increases in muscle AMPK signaling, free AMP content and glucose disposal during exercise are largely determined by the absolute exercise intensity, whilst increases in plasma catecholamine levels, muscle glycogen use and muscle lactate levels are more closely associated with the relative exercise intensity.




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