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 VO2maxwas 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 profile toward only two different clusters (analogous to a fiber type classification, that is, slow and fast twitch fibers). This shift was primarily due to a significant training‐induced increase in SDH activity (mean, 75%) among the fibers. The enhanced performance during the 60‐minute endurance cycle test and VO2maxtest following training may be partly explained by an individual single fiber metabolic profile change.