STUDY ON COMPARTMENTALIZATION, DIS-TRIBUTION AND CROSS-SECTIONAL AREAS OF FIBER TYPES IN HUMAN DELTOID MUSCLE / 解剖学报

ABSTRACT

The deltoid muscles on both sides of 8 male cadavers were studied within 24 hours after death. According to its fiber architecture, origins and insertions, and nerve distribution, the deltoid muscle was divided into three compartments an anterior, a middle and a posterior. The muscle samples were taken respectively from the superficial and the deep portion of each compartment of the deltoid muscle. Frozen transverse sections were stained fer myosin ATPase. Muscle fibers were identified as type Ⅰ and type Ⅱ. The proportion of fiber types in each portion was calculated on microscopic photographs and mean cross-sectional areas of both fiber types were measured by imaging analytical system. The results showed that the proportion of type Ⅰ fiber in the superficial and deep portion of the middle compartment is significantly higher than that of the corresponding portion of the anterior and posterior compartments, and the proportion in the deep portion of each compartment is higher than that of the superficial one, however no difference was found between the left and right sides. The fiber size among all portions is not obviously different, but the diameter of type Ⅱ fiber in the deep portion of the middle compartment is significantly smaller than that of other portions. Except the deep portion of the middle compartment, the diameter of both fiber types of the right muscle is larger than those of the left one, although statistical analysis showed that the difference is not significant. The authors suggest that the difference of fiber type distribution within the deltoid muscle is closely related with the functional differentiation of the muscle and the characteristic higher typeⅠ fiber proportion and smaller type Ⅱ fiber diamiter in the deep portion of the middle compartment probably indicate that the main function of this portion is to keep the shoulder joint stability.