Metabolic adaptations in single muscle fibers of competitive endurance cyclists

Selected enzymes were studied in single muscle fiber preparations taken from eight competitive cyclists (six male, two female) previous to and after 8 weeks of progressive heavy endurance training (85% maximal oxygen consumption [VO2max], 60 minutes a day, 5 days a week). Mean + SD VO2max was significantly increased (3.71 ± 0.62 to 4.15 ± 0.65 L.min‐1), as was mean, submaximal endurance power output (150 ± 24 to 204.8 ± 36.9 W) on a 60‐minute endurance cycle test after training. In single vastus lateralis fiber preparations obtained from a biopsy sample before and after training, the activity of succinate dehydrogenase (SDH), lactate dehydrogenase (LDH), and myofibrillar adenosine triphosphatase (mATPase) was determined using quantitative histochemical and image analysis technique. A cluster analysis of data defined three distinct fiber metabolic profiles (that is, different interrelationships among SDH, LDH, mATPase activity) prior to training. Following training, there was a shift in the metabolic profi...