Motor unit fibre density in the extensor digitorum communis muscle. Single fibre electromyographic study in normal subjects at different ages.

A single fibre EMG study is presented from extensor digitorum communis muscle in sujbects aged 10 to 89 years. The average number of single muscle fibre action potentials generated by muscle fibres in the same motor unit within the uptake area of the electrode is used as a measure of the motor unit fibre density. The fibre density increases slowly during life with a faster progression after the age 70 years. The number of recordings indicating impaired nerve or neuromuscular impulse transmission increases at the same time. The findings indicate degenerative loss of motor neurones with aging, compensated for by reinnervation. The changes are relatively slight in the extensor digitorum communis muscle as compared with other muscles, permitting early pathological changes in this muscle to be recognized independently of age factors.