[Histochemical and morphometric studies of the musculature of the forelimb of sheep with reference to its function. 2. Flexor and extensor of carpal and toe joints].
Muscle tissue was obtained from eight forearm muscles of six male sheep (180 days old) and stained for NADH tetrazolium oxidoreductase and myofibrillar ATPase after preincubation at pH 4.3. The fiber diameter and the percentage were determined of three fiber types: slow twitch oxidative (STO), fast twitch oxidative (FTO) and fast twitch glycolytic fibers (FTG). The extensor carpi radialis muscle had the lowest percentage of STO fibers. It is a fast extensor of the carpal joint. The superficial digital flexor muscle (FS) is located in the superficial region of the forearm has shown the highest percentage of STO fibers (50%). These fibers were also considerable larger (57 microns) than the STO fibers of the deep digital flexor muscle (39 microns). The FS supports the elbow joint extensors in the fixation of the elbow joint during the standing position (static work) and flexes the digital joints in motion (dynamic work). At first muscle function decides the quality and the quantity of the muscle fibers. Then other factors, e.g. capillarization, determine the distribution of fiber types. Muscles which have to work static-tonically require a higher content of large slow twitch fibers regardless of whether these muscles are located close to the limb axis or in the periphery. They resist lastingly gravity. Thus they are antigravity muscles. In the forearm they are the superficial digital flexor muscle, flexor carpi ulnaris muscle, and extensor carpi ulnaris muscle, which always have more than 30% STO-fibers.