The identification of fiber types in skeletal muscle: a continual dilemma

We have attempted to present an overview of some of the methods used for identifying and studying the fibers and motor units of skeletal muscle, and to give a short discourse on the particular strengths and weaknesses of these methods. It was not our intention to reach a final conclusion of there being only one way to identify muscle fibers or that the subject is closed to additional research. Quite the contrary, we intended to demonstrate that in the past two decades there has been an explosion of knowledge in this field. In the introduction, we suggested that the era of a simple classification scheme for categorizing fibers has passed. We also posed a number of questions. It seems that an appropriate conclusion would be to return to these questions with some answers. Our first question was "what is the purpose of fiber typing?" To us, its intent is to provide as much information as possible about fibers, accentuating their similarities and differences, such that the designated groupings are most meaningful. This has become increasingly difficult as the complex nature of skeletal muscle fibers has been unravelled and the diversity of those fibers previously thought to be similar is exposed. However, fiber typing schemes provide valuable information concerning the nature of the fibers and are important in attempting to describe the nature of muscle. Therefore, fiber typing is a necessary step in describing the complex characteristics of skeletal muscle. We also asked "is more information needed?" Clearly more information is needed to develop a complete understanding of the biochemical and functional aspects of muscle and how it adapts to a variety of experimental or naturally occurring perturbations. Thus, as time passes and more information is amassed, a constant revision of the schemes for identifying fibers can be expected. This is a positive sign of a viable field. A third question was "is it worth trying to keep up or can one be expected to keep up with the seemingly rapid changes in the identification schemes used for fiber typing?" This seems like an absurd question, and yet, it has been posed to us by university professors who are "comfortable with" and continue to use the old system(s) of muscle and fiber identification and who do not want to "see things change." This question, when asked in any field, implies an unwillingness to make the effort to stay abreast with advancements occurring in that field.(ABSTRACT TRUNCATED AT 400 WORDS)