Increased muscle oxidative potential following resistance training induced fibre hypertrophy in young men.

Some evidence suggests that resistance training may lower relative muscle mitochondrial content via "dilution" of the organelle in a larger muscle fibre. Such an adaptation would reduce fatigue resistance, as well as compromise oxidative ATP synthesis and the capacity for fatty-acid oxidation. We investigated the effect of resistance training on mitochondrial enzymes of the citric acid cycle (citrate synthase; CS) and beta-oxidation (beta-hydroxyacyl CoA dehydrogenase; beta-HAD), as well as markers of the potential for glucose phosphorylation (hexokinase; HK) and glycolysis (phosphofructokinase; PFK). Twelve untrained men (21.9 +/- 0.5 y; 1.79 +/- 0.03 m; 83.2 +/- 3.2 kg) participated in a 12 week progressive resistance-training program. Muscle biopsies were taken from the vastus lateralis before (PRE) and after (POST) training. Training increased mean muscle fibre cross-sectional area (p < 0.05) and the activities of CS (PRE = 4.53 +/- 0.44 mol.kg protein(-1).h(-1); POST = 5.63 +/- 0.40 mol.kg protein(-1).h(-1); p < 0.001) and beta-HAD (PRE = 2.55 +/- 0.28 mol.kg protein(-1).h(-1); POST = 3.11 +/- 0.21 mol.kg protein(-1).h(-1); p < 0.05). The activity of HK increased 42% (p < 0.05), whereas the activity of PFK remained unchanged. We conclude that resistance training provides a stimulus for improving muscle oxidative potential, as reflected by the increased activities of CS and beta-HAD following resistance training induced hypertrophy.