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 (V̇o2max) 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 (V̇GM), pyruvate (V̇Pyr), palmitoyl carnitine (V̇PC)], and the activity of the mitochondrial respiratory complexes II and IV were assessed using succinate (V̇s) and N,N,N′,N′-tetramethyl-p-phenylenediamine dihydrochloride (V̇TMPD), respectively. V̇o2max was higher in ATH than in SED (57.8 ± 2.2 vs. 31.4 ± 1.3 ml·min−1·kg−1, P < 0.001). V̇GM 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). V̇Pyr 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 V̇PC was not significantly different (5.3 ± 0.9 vs. 4.4 ± 0.5 μmol O2·min−1·g dry wt−1). V̇S 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 V̇TMPD (20.1 ± 1.0 vs. 16.2 ± 3.4 μmol O2·min−1·g dry wt−1, P < 0.05). The ratios V̇S/V̇GM (1.3 ± 0.1 vs. 2.0 ± 0.1, P < 0.001) and V̇TMPD/V̇GM (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.
- exercise training
- Copyright © 2008 the American Physiological Society