EFFECTS OF SPRINT CYCLE TRAINING ON HUMAN SKELETAL-MUSCLE

Eleven men sprint trained two to three times per week for 6 wk to inve stigate possible exercise-induced slow-to-fast fiber type conversions. Six individuals served as controls. Both groups were tested at the be ginning and end of the study to determine anaerobic performance and ma ximal oxygen consumption. In addition, pre- and postbiopsies were extr acted from the vastus lateralis muscle and were analyzed for fiber typ e composition, cross-sectional area, and myosin heavy chain (MHC) cont ent. No significant changes were found in anaerobic or aerobic perform ance variables for either group. Although a trend was found for a decr ease in the percentage of type IIb fibers, high-intensity sprint cycle training caused no significant changes in the fiber type distribution or cross-sectional area. However, the training protocol did result in a significant decrease in MHC IIb with a concomitant increase in MHC IIa for the training men. These data appear to support previous invest igations that have suggested exercise-induced adaptations within the f ast fiber population (IIb --> IIa) after various types of training (en durance and strength).