STRETCH ACTIVATION OF SKELETAL-MUSCLE FIBER TYPES

In a number of studies it has been attempted to build up a correlation between maximal unloaded shortening velocity and the different fibre types of skeletal muscles; but not always a correlation was observed. In the present study on histochemically defined fibre types of rat, fi sh, crayfish and locust skeletal muscles, it has been found that the k inetics of stretch-induced delayed force increase (stretch activation) shows a much greater variance and a stronger correlation with fibre t ype than does unloaded shortening velocity. Thus, the stretch activati on experiment allows a reliable identification of muscle fibre types. In addition, information can be deduced about crossbridge cycling step s in muscle fibre types and their determination by myofibrillar protei ns.