The value of enzyme histochemical techniques in classifying fibre types of human skeletal muscle. 1. Adult skeletal muscles with no apparent disease of the neuromuscular system.

Fibre-type classification of human skeletal muscle into type I and type II fibres is mostly based on their slight or strong staining with the myosin adenosine triphosphatase reaction. In order to evaluate the reliability of this screening technique a combined histochemical and biochemical study was performed on normal and diseased skeletal muscle of human subjects. In the present investigation activities of enzymes which play a role in the aerobic and anaerobic pathways and which can characterize fibre type, were examined in muscle specimens, with no apparent disease of the neuromuscular system. Special attention is given to the maximal activities of phosphofructokinase and fructose-1,6-diphosphatase, the rate limiting enzymes for the regulation of the glycolysis and glyconeogenesis, respectively. A most important feature of the biochemical findings is the constancy of the activity ratios of the examined enzymes. From these results and from the histochemical results it can be concluded that in apparently normal adult human skeletal muscle the ATP-ase technique for type I and type II typing is reliable. For fibres with an intermediate intensity of staining with the myosin ATPase technique of typing it is also necessary to apply other enzyme histochemical techniques.