Biometrical and histochemical comparison between extra- and intrafusal muscle fibres following tenotomy.

The average diameter of the different enzymatic types of extra- and intrafusal muscle fibres is determined by means of a one millimeter scale ocular micrometer in the gastrocnemius muscle of twenty four female rats during three months, at regular intervals following tenotomy. There is a predominant atrophy of the type II extrafusal as well as intrafusal fibres in the period of immobilization. However, when the muscle becomes functional again, by healing and elongation of the tendon, the intrafusal type II fibres remain atrophic in contrast to the extrafusal ones, which regain their normal size.