Objective
The purpose of this study is to compare muscle strength, endurance and the change of myosin heavy chain isoform after sprint training(ST) and heavy resistance training(HRT).

Method
Fourteen young athletes were enrolled and were randomly assigned into each training group. Before and after training for 8 weeks, the strength and the endurance were evaluated using isokinetic exercise system(Cybex 6000). The specimens of muscle biopsy were obtained from vastus lateralis muscle and were analysed for muscle fiber type using one dimensional electrophoresis.

Results
Peak torque, total work and mean power were increased significantly in both groups, but endurance ratio increased only in the sprint training group(P＜0.05).

The proportions of myosin heavy chain(MHC) IIa fibers were increased in both groups and those of MHC IIb fibers were decreased in both groups(P＜0.05). MHC I fibers were significantly increased in ST group, but decresed in HRT group(P＞0.05).

Conclusion
This study shows that it is possible to increase muscle strength and to achieve fiber type transformation with the sprint training and the high resistance training.