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

The adaptation of muscle oxidative function to 6 weeks of endurance cycle training was investigated in eight untrained subjects. Peak oxygen consumption ((V) over dot O-2peak) increased by 24% (2.69 +/-0.21 versus 3.34 +/-0.30 l O-2 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 ((V)over dot(O)) of skinned fibres increased by 35% (0.170.01 versus 0.23 +/-0.01 mmol O-2. min(-1). kg(-1) wet weight, P <0.05) and maximal ADP-stimulated respiration ((V) over dot(max)) increased by 38% (1.17 +/-0.07 versus 1.62 +/-0.14 mmol O-2. min(-1). kg(-1) wet weight, P<0.05). ADP sensitivity [i.e. the ratio between mitochondrial respiration (after correction for (V) over dot(O)) at 0.1 mM ADP and (V) over dot(max)] was reduced after training (0.400.05 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.