Worldwide, numerous textbooks and publications have dealt with research on muscle fibres carried out under different points of view. In addition, comprehensive works such as Myology (Engel and Franzini-Armstrong 1994), Disorders of Voluntary Muscle (Walton et al. 1994), and Skeletal Muscle (Schmalbruch 1985) as a volume ofthe work Handbook of Microscopic Anatomy, have been published. Moreover, proceedings from myology symposiums give us access to the present state of the art in muscle research. The book The Dynamic State of Muscle Fibres (Pette 1990a) summarizes the contributions to the symposium of the same name, which was held in Constance in 1989. Considering these outstanding works one has to ask the question: Why do we need the present book? The first reason is that results from ongoing research expand scientific knowledge continuously. When dealing with muscle research one soon realizes that muscle tissue is a fascinating subject, whose secrets have not yet been revealed completely. The application of new techniques in muscle fibre research enables and provokes us to go deeper into the nature of muscle tissue. The results are findings that add a new dimension to what is already known. For instance, the detailed metabolic charac terization of muscle fibre types in the context of an intact histological section has been performed only recently using cytophotometrical quantification of enzyme activities. The second reason for this book is of a more pragmatic nature.