Myoglobin concentration in single type I and type II muscle fibres in man.

Histochemical visualization of myoglobin in a benzidine peroxidase reaction suggests that human skeletal muscle fibres are differentiated into fibres having either high or a low myoglobin content. In the present study myoglobin was quantified in single human muscle fibres after being classified as either type I ("slow-twitch") or type II ("fast twitch"). Samples were obtained from m. quadriceps femoris in 4 healthy untrained male subjects using the needle biopsy technique. After freeze-drying, individual fibres were dissected out and classified as either type I or type II by a myofibrillar ATPase stain. Myoglobin analyses were performed on these single fibres by a radioimmunoassay. The myoglobin concentrations were found to be significantly higher in type I than in type II muscle fibres in all 4 subjects and were, on the average, of the same magnitude as found in larger (mixed muscle) samples. The myoglobin concentration ratio between type I and type II fibres ranged from 1.4 to 1.7.