ABSTRACT
The thoroughbred horse is a remarkable animal, with both speed and endurance abilities during running. Muscle adaptation associated with training and growth has been examined using various physiological, histochemical and biochemical measurements. We have emphasized the importance of type IIX fiber recruitment in training program for thoroughbred. Because type IIX fiber provides the greatest contribution to total muscle volume in the gluteus medius muscle and increases in oxidative enzymes of the fibers would markedly improve the whole-muscle oxidative capacity. Based on these concepts, we examined the adaptations of type IIX fiber including hybrid fiber to various training programs.It is considered that scientific information about optimal training of these excellent abilities can provide significant insights into exercise physiology and health science not only for thoroughbred horses, but also for human beings.