Histochemistry and morphometry of ovine forearm musculature in relation tofunction. Part 2. Flexors and extensors of carpal and digital joints

Muscle tissue was obtained from eight forearm muscles of six male sheep (18 0 days old) and stained for NADH tetrazolium oxidoreductase and myofibrilla r ATPase after preincubation at pH 4.3. The fiber diameter and the percenta ge 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 t he highest percentage of STO fibers (50%). These fibers were also considera ble larger (57 mu m) than the STO fibers of the deep digital flexor muscle (39 mu m). The FS supports the elbow joint extensors in the fixation of the elbow joint during the standing position (static work) and flexes the digi tal joints in motion (dynamic work). At first muscle function decides the q uality and the quantity of the muscle fibers. Then other factors, e.g. capi llarization, determine the distribution of fiber types. Muscles which have to work static-tonically require a higher content of large slow twitch fibe rs regardless of whether these muscles are located close to the limb axis o r in the periphery. They resist lastingly gravity. Thus they are antigravit y muscles. In the forearm they are the superficial digital flexor muscle, f lexor carpi ulnaris muscle, and extensor carpi ulnaris muscle, which always have more than 30% STO-fibers.