Fiber type composition of the hip abductor muscles

Abstract

Objectives: The hip abductor muscles; gluteus medius, gluteus minimus and tensor fasciae latae, play an important role in pelvic stabilization. Morphological changes occur in these muscles as a consequence of chronic musculoskeletal conditions (e.g. osteoarthritis), aging, and following hip joint replacement. Functional studies show unique activation profiles of the different compartments of gluteus medius and gluteus minimus; however, little is known of the fiber type composition of these muscles, which is an important consideration for understanding their functional and metabolic capabilities. Methods: Eight transverse muscle samples from each compartment of gluteus medius and gluteus minimus, and two samples from tensor fasciae latae were harvested from 11 cadavers, and processed for immunohistochemistry. Fast-twitch muscle fibers were stained with the MY-32 antibody to estimate the proportion of type II fibers comprising the muscles. Results: Individual muscle fiber composition profiles demonstrated that gluteus medius and gluteus minimus were similar in composition, supporting a predominantly postural function. Tensor fasciae latae had a higher proportion of type II fibers, suggesting a more phasic functional role. No differences were observed between compartments for gluteus medius, but the anterior compartment of gluteus minimus had a significantly higher proportion of type II fibers than the posterior. Conclusion: This study provides anatomical data for the fiber type composition profiles of the hip abductor muscles, contributing to the understanding of their metabolic and contractile capabilities. These data may be valuable when considering changes that occur at the cellular level in the hip abductor muscles under pathological conditions and with aging.