Journal of Applied Physiology AJP: Cell Physiology
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J Appl Physiol 102: 1844-1849, 2007. First published January 18, 2007; doi:10.1152/japplphysiol.01173.2006
8750-7587/07 $8.00
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Reduced efficiency, but increased fat oxidation, in mitochondria from human skeletal muscle after 24-h ultraendurance exercise

Maria Fernström,1,2 Linda Bakkman,1,2 Michail Tonkonogi,2,3 Irina G. Shabalina,2 Zinaida Rozhdestvenskaya,2 C. Mikael Mattsson,1,2 Jonas K. Enqvist,1,2 Björn Ekblom,1,2 and Kent Sahlin1,2,4

1Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm; 2Åstrands Laboratory, The Swedish School of Sport and Health Sciences (GIH), Stockholm; and 3University of Dalarna, Falun, Sweden; and 4Institute of Sport Sciences and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark

Submitted 18 October 2006 ; accepted in final form 8 January 2007

The hypothesis that ultraendurance exercise influences muscle mitochondrial function has been investigated. Athletes in ultraendurance performance performed running, kayaking, and cycling at 60% of their peak O2 consumption for 24 h. Muscle biopsies were taken preexercise (Pre-Ex), postexercise (Post-Ex), and after 28 h of recovery (Rec). Respiration was analyzed in isolated mitochondria during state 3 (coupled to ATP synthesis) and state 4 (noncoupled respiration), with fatty acids alone [palmitoyl carnitine (PC)] or together with pyruvate (Pyr). Electron transport chain activity was measured with NADH in permeabilized mitochondria. State 3 respiration with PC increased Post-Ex by 39 and 41% (P < 0.05) when related to mitochondrial protein and to electron transport chain activity, respectively. State 3 respiration with Pyr was not changed (P > 0.05). State 4 respiration with PC increased Post-Ex but was lower than Pre-Ex at Rec (P < 0.05 vs. Pre-Ex). Mitochondrial efficiency [amount of added ADP divided by oxygen consumed during state 3 (P/O ratio)] decreased Post-Ex by 9 and 6% (P < 0.05) with PC and PC + Pyr, respectively. P/O ratio remained reduced at Rec. Muscle uncoupling protein 3, measured with Western blotting, was not changed Post-Ex but tended to decrease at Rec (P = 0.07 vs. Pre-Ex). In conclusion, extreme endurance exercise decreases mitochondrial efficiency. This will increase oxygen demand and may partly explain the observed elevation in whole body oxygen consumption during standardized exercise (+13%). The increased mitochondrial capacity for PC oxidation indicates plasticity in substrate oxidation at the mitochondrial level, which may be of advantage during prolonged exercise.

P/O ratio; uncoupling protein 3; fatty acid oxidation


Address for reprint requests and other correspondence: K. Sahlin, The Swedish School of Sport and Health Sciences (GIH), Box 5626, SE 114 86 Stockholm, Sweden (e-mail: kent.sahlin{at}gih.se)






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