Effect of endurance training on oxidative and antioxidative function in human permeabilized muscle fibres

Abstract.

The adaptation of muscle oxidative function to 6 weeks of endurance cycle training was investigated in eight untrained subjects. Peak oxygen consumption ($\dot VO_{2peak}$ ) increased by 24% (2.69±0.21 versus 3.34±0.30 l O₂ min^–1, mean ±SEM, P<0.01) and lactate threshold intensity increased by 53% (121±13 versus 185±15 W, P<0.01) following the training period. Muscle biopsy samples were taken from vastus lateralis before and after training, and respiration in permeabilized muscle fibres was measured. Following training, non-ADP-stimulated respiration ($\dot V_o$ ) of skinned fibres increased by 35% (0.17±0.01 versus 0.23±0.01 mmol O₂·min^–1·kg^–1 wet weight, P<0.05) and maximal ADP-stimulated respiration ($\dot V_{\max }$ ) increased by 38% (1.17±0.07 versus 1.62±0.14 mmol O₂·min^–1·kg^–1 wet weight, P<0.05). ADP sensitivity [i.e. the ratio between mitochondrial respiration (after correction for $\dot V_o$ ) at 0.1 mM ADP and $\dot V_{\max }$ ] was reduced after training (0.40±0.05 versus 0.26±0.02; P<0.05). Mitochondrial resistance to oxidative stress was investigated by exposing skinned fibres to exogenous reactive oxygen species (ROS). ADP-stimulated respiration was reduced after ROS exposure and the relative decrease was similar before and after training. It is concluded that after endurance training: (1) the relative increase in maximal muscle fibre respiration exceeds that of whole-body oxygen uptake; (2) the sensitivity of mitochondrial respiration to ADP decreases; and (3) the impairment of oxidative function in skinned muscle fibres by ROS remains unchanged.