Stretch activation of skeletal muscle fibre 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, fish, crayfish and locust skeletal muscles, it has been found that the kinetics of stretch-induced delayed force increase (stretch activation) shows a much greater variance and a stronger correlation with fibre type than does unloaded shortening velocity. Thus, the stretch activation experiment allows a reliable identification of muscle fibre types. In addition, information can be deduced about crossbridge cycling steps in muscle fibre types and their determination by myofibrillar proteins.