Skeletal muscle is a heterogeneous tissue comprising different types of fibres. Traditionally, fibre types are classified as slow-oxidative (b-red), fast oxidative-glycolytic (a-red), and fast-glycolytic (a-white) fibres, according to their histochemical staining properties. The composition of fibre types varies between anatomical muscles, according to functional loads, such that muscles for postural maintenance tend to have fibres with higher oxidative capacity than those muscles solely used for rapid and forceful contractions, such as running. Metabolic, biochemical and biophysical characteristics, such as oxidative and glycolytic capacities, fibre size, colour, and glycogen and lipid contents, have been found to vary between muscle fibre types. Not surprisingly, therefore, fibre type composition can have profound influence on post-mortem changes in the conversion of muscle to meat, and its subsequent effect on
product quality. Some recent studies found correlations between fibre type or size, and eating quality, in particular tenderness in beef. Large fast glycolytic fibres were found to negatively correlate with tenderness, and slowoxidative fibres were found to positively associate with tenderness. In modern pigs, the results of intensive selection, where high proportions of large fast fibres are often present, inadequate perfusion of metabolic substrates (such as oxygen) and by-products (such as lactate) is more likely to occur, which can adversely affect meat quality. Although the important linkbetw een fibre types and
meat quality is well recognised, the precise relationship between a type of fibre and a particular meat quality trait remains poorly defined. This is partly due to the necessarily subjective nature of measuring certain meat quality traits, such as eating qualities, and partly due to inconsistency in defining fibre types in farm animals. A major limitation of fibre typing farm animal skeletal muscle has been the near exclusive use of histochemistry. Histochemical methods, such as succinate dehydrogenase and myosin
ATPase stainings, are invaluable in describing the biochemical status of individual fibres, but are less reliable in defining fibre types. Different histochemical stains often do not give an identical classification outcome. Inconsistent fibre type classification can therefore lead to confusing association results between
meat quality traits and fibre type characteristics.