Introduction

Abstract

The differentiation of muscle into red and white types is a feature of all vertebrates and, indeed, of chordates. Red muscles are slow-contracting and specialized for postural activity. They contain plentiful lipid droplets and glycogen granules and sparse mitochondria. White muscles, on the other hand, are faster contracting, suitable for short bursts of intense activity, but fatigue rapidly. They contain few lipid droplets, but plentiful mitochondria. In man these fibre types are not found exclusively in individual muscles but occur in a random distribution in all muscles. Although these two types of muscle fibre can be recognized in haematoxylin and eosin preparations of transverse sections of paraffin-embedded muscle, they can be more easily identified by the reciprocal relationship of their content of oxidative and non-oxidative enzymes (see Table 2.3). The red fibres react strongly for oxidative enzymes, e.g. succinic dehydrogenase, and are designated Type 1 fibres, and the white fibres react strongly for non-oxidative enzymes, e.g. myophosphorylase, and are designated Type 2 fibres (Dubowitz and Pearse, 1960). In cross section these two fibre types are arranged in a random mosaic pattern within muscle fascicles.