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Training at high exercise intensity promotes qualitative adaptations of mitochondrial function in human skeletal muscle

¹Physiology and Functional Explorations Department, Centre Hospitalier Régional Universitaire of Strasbourg, Strasbourg; ²Physiology Department, Faculty of Medicine, University Louis Pasteur, Équipe d'Accueil 3072, Strasbourg; ³Institut National de la Santé et de la Recherche Médicale, U769, Châtenay-Malabry; ⁴University Paris-Sud, Châtenay-Malabry; and ⁵Cardiology Department, Civil Hospital, Colmar, France

Submitted 24 October 2007 ; accepted in final form 16 February 2008

This study explored mitochondrial capacities to oxidize carbohydrate and fatty acids and functional optimization of mitochondrial respiratory chain complexes in athletes who regularly train at high exercise intensity (ATH, n = 7) compared with sedentary (SED, n = 7). Peak O₂ uptake (O_2max) was measured, and muscle biopsies of vastus lateralis were collected. Maximal O₂ uptake of saponin-skinned myofibers was evaluated with several metabolic substrates [glutamate-malate (_GM), pyruvate (_Pyr), palmitoyl carnitine (_PC)], and the activity of the mitochondrial respiratory complexes II and IV were assessed using succinate (_s) and N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride (_TMPD), respectively. O_2max was higher in ATH than in SED (57.8 ± 2.2 vs. 31.4 ± 1.3 ml·min^–1·kg^–1, P < 0.001). _GM was higher in ATH than in SED (8.6 ± 0.5 vs. 3.3 ± 0.3 µmol O₂·min^–1·g dry wt^–1, P < 0.001). _Pyr was higher in ATH than in SED (8.7 ± 1.0 vs. 5.5 ± 0.2 µmol O₂·min^–1·g dry wt^–1, P < 0.05), whereas _PC was not significantly different (5.3 ± 0.9 vs. 4.4 ± 0.5 µmol O₂·min^–1·g dry wt^–1). _S was higher in ATH than in SED (11.0 ± 0.6 vs. 6.0 ± 0.3 µmol O₂·min^–1·g dry wt^–1, P < 0.001), as well as _TMPD (20.1 ± 1.0 vs. 16.2 ± 3.4 µmol O₂·min^–1·g dry wt^–1, P < 0.05). The ratios _S/_GM (1.3 ± 0.1 vs. 2.0 ± 0.1, P < 0.001) and _TMPD/_GM (2.4 ± 1.0 vs. 5.2 ± 1.8, P < 0.01) were lower in ATH than in SED. In conclusion, comparison of ATH vs. SED subjects suggests that regular endurance training at high intensity promotes the enhancement of maximal mitochondrial capacities to oxidize carbohydrate rather than fatty acid and induce specific adaptations of the mitochondrial respiratory chain at the level of complex I.

metabolism; exercise training