Architectural and histochemical properties of cat hip 'cuff' muscles.

The architectural properties and fiber-type composition of the cat hip 'cuff' muscles, i.e. the deep layer of muscles encircling the hip joint, were determined. The muscles studied included the gluteus minimus, obturator internus and externus, gemellus superior and inferior, pyriformis, quadratus femoris and capsularis. In addition, the fiber-type composition was determined for the iliacus muscle. Compared to other lower limb muscles, the cuff muscles were small (approximately 0.2 to 2.7 g) and short (approximately 15 to 40 mm long) and had short mean fiber lengths (approximately 7 to 12 mm long), small angles of fiber pinnation (< or = 12 degrees), and small physiological cross-sectional areas (approximately 0.2 to 2.8 cm2). The percentage of the cross-sectional area comprised of slow fibers ranged from 24 to 95% with this value being over 50% in 5/9 muscles studied. The small angle of pinnation and short fiber lengths optimize force production and the relatively high percentage of slow fibers suggest a high level of activation. Both of these properties are consistent with a hip stabilization role for these muscles. In addition, the high percentage of slow fibers suggests a high spindle density and a possible role of these muscles in providing proprioceptive feedback to the central nervous system for the control of posture and locomotion.