Histochemical Demonstration of Myoglobin in Skeletal Muscle Fibres and Muscle Spindles

Abstract

MOST muscles are composed of a mixture of two types of muscle fibre which can be shown to differ in myoglobin content. Slow type 1 fibres are narrow, contain numerous mitochondria and are poor in glycogen and phosphorylase. Fast type 11 fibres are broad, contain few mitochondria and are rich in glycogen and phosphorylase1. It has been assumed that type 1 fibres are rich in myoglobin and these are termed red. Type 11 fibres are assumed to be poor in myoglobin and are termed white. Similarly, it has been assumed that the large nuclear bag fibres of muscle spindles are poor in myoglobin and that they contract rapidly. The smaller nuclear chain fibres would be expected to be rich in myoglobin and contract slowly. No comprehensive survey of the myoglobin content of muscle fibres has previously been reported. Knowledge of the precise distribution of myoglobin in extrafusal and intrafusal fibres would throw light on the function of myoglobin and muscle spindle activity.