Muscle morphology and metabolic potential in elite road cyclists during a season.

The purpose of this investigation was to study muscle adaptation to high endurance performance. Muscle biopsies were taken from the m. vastus lateralis of 23 road cyclists, and their VO2 max was measured repeatedly during the season. At the beginning of their training season, VO2 max was 56 (37-66) ml X min-1 X kg-1 in competitive amateurs and 71 (64-76) ml X min-1 X kg-1 in elite professionals. Muscle capillary density determined at the same time was correspondingly roughly 30% higher in elite than in competitive cyclists while muscle enzyme activities (CS, HAD, and HK) were 30%-60% higher and LDH 50% lower in elite compared to competitive cyclists. Some elite cyclists were retested 5 months later when each of them had completed more than 15,000 km of bicycling during training and competition. During this period VO2 max remained unchanged, and the same was true for capillary density, while muscle enzyme activity (CS, HAD, and HK) increased 40%-70%, and LDH slightly decreased. The present results suggest that there may not be a close coupling between whole body VO2 max and the oxidative capacity of a local muscle group. Rather, the changes in muscle enzyme activities may be of importance for the regulation of muscle metabolism enhancing the endurance capacity. It is suggested that capillary density of the working muscles is of significance for VO2 max.