Variability of muscle fibre composition and fibre size in the horse gluteus medius: an enzyme-histochemical and morphometric study
López-Rivero, J.L.; Serrano, A.L.; Diz, A.M.; Galisteo, A.M.
Journal of Anatomy 181: 1-10
1992
ISSN/ISBN: 0021-8782 PMID: 1284127 Document Number: 402274
To determine the variability in fibre types and fibre size in the equine gluteus medius muscle, biopsy specimens were removed from 5 sites, at 4 different depths, within the right and left muscles of 3 Andalusian stallions. The percentage, lesser fibre diameter and cross-sectional area of the various fibre types were measured systematically in myosin ATPase and NADH-tetrazolium reductase-stained, serial cryostat sections of these multiple samples. Significant differences in muscle fibre type compostion were recorded, with a lower percentage of type I fibres (high myosin ATPase activity at pH 4.5) being observed towards superficial regions of the muscle and a greater percentage towards the deep areas. Type IIB fibers (moderate myosin ATPase activity at pH 4.5), including both IIB nonoxidative (low NADH-TR activity) and IIB oxidative (moderate NADH-TR activity), displayed the opposite tendency, and the percentage of type IIA fibers (low myosin ATPase activity at pH 4.5) did not change with depth. Types I and IIA fibers in the deep regions were larger than superficially, whereas the IIB fibres in the deep regions were smaller than in the superficial parts of the muscle. The results also imply that type I fibres tend to be larger than type II fibres in the deep regions. The size of type I fibres is more homogeneous in the deep parts than in the superficial regions of the muscle, while IIB fibres vary more in size in the peripheral portion than in deep regions. A single biopsy taken from the gluteus medius muscles of the horse is therefore a poor representative of the whole muscle and care should be exercised in sampling and interpreting data obtained from limited biopsy of this muscle. The patterns of variation in fibre types and fibre sizes between the different depths of the muscle probably reflect different functional demands on the gluteus medius muscle.