Muscle fiber compartmentalization in the gluteus medius of the horse

Abstract

Muscle fiber architecture, innervation, and differences in fiber-type composition were examined in the gluteus medius of four horses. In the anatomical part of this study, the gluteus medius of four adult horses were extracted, soaked in a 10% formalin solution, and examined for fiber architecture and innervation patterns. Based on architectural and innervation differences, two distinct anatomical compartments were defined: the dorsal region and the ventral region. The histochemical portion of this study examined the fiber composition of each region by classifying the fiber types on the basis of myosin-ATPase. The dorsal region had a significantly higher percentage of Type I fibers than the ventral region; whereas the ventral region had a significantly higher percentage of Type IIB fibers than the dorsal region. These findings suggest that this subdivided structure may be designed to allow functional independence within the muscle.