Fibre type composition of the human psoas major muscle with regard to the level of its origin

Abstract

The aim of our study was to explore the fibre type composition of the human psoas major muscle at different levels of its origin, from the first lumbar to the fourth lumbar vertebra, and to compare the muscle fibre size and distribution of different fibre types between levels with respect to its complex postural and dynamic function. Muscle samples were collected from 15 young males (younger than 35 years). Serial transverse sections (5 lm) of the samples were cut by cryomicrotome. Type I, IIA and IIX muscle fibres were typed using myosin heavy chain identification. The serial sections were analysed using a light microscope with a magnitude of 100·. The differences between measurements were evaluated using a repeated-measures ANOVA and Scheffé test for post-hoc analysis. Our study showed that the human psoas major muscle was composed of type I, IIA and IIX muscle fibres. It had a predominance of type IIA muscle fibres, whereas type I muscle fibres had the largest cross-sectional area. Type IIX muscle fibres were present as a far smaller percentage and had the smallest crosssectional area. Moreover, the fibre type composition of the psoas major muscle was different between levels of its origin starting from the first lumbar to the fourth lumbar vertebra. We conclude that the fibre type composition of the psoas major muscle indicated its dynamic and postural functions, which supports the fact that it is the main flexor of the hip joint (dynamic function) and stabilizer of the lumbar spine, sacroiliac and hip joints (postural function). The cranial part of the psoas major muscle has a primarily postural role, whereas the caudal part of the muscle has a dynamic role.

Sex Differences in the Cross-sectional Areas of Psoas Major and Thigh Muscles in High School Track and Field Athletes and Nonathletes

“…As described earlier, trunk muscles have a critical role in the maintenance of stability and balance when performing movements with the extremities (Andersen et al, 1988), and a strong and stable trunk provides a solid foundation for the torques generated by the limbs (Behm and Anderson, 2006;Kibler et al, 2006). Among the muscle groups located in the trunk, PM is the only muscle that connects the lumber spine and lower limbs (Arbanas et al, 2009). Taking this into account together with previous findings on sex differences in muscular distribution (Abe et al, 2003;Janssen et al, 2000) and strength (Bishop et al, 1987), therefore, the greater PM CSA in the boys compared to the girls might be assumed to be a functional requirement associated with greater development in the muscle mass and strength capability of the upper extremity and trunk.…”

“…However, Alway et al (1989) reported that, for biceps brachii, the ratio of type II fiber area to LBM was higher in male bodybuilders than in female bodybuilders, but the corresponding ratio for type I fibers was similar between the two groups. Arbanas et al (2009) indicated that the human psoas major muscle has a predominance of type IIA fibers. Considering these findings, therefore, the possible difference in the size of type II fibers between the boys and girls might also be a reason for the sex difference observed in PM CSA/ LBM 2/3 .…”

“…Trunk muscles have a critical role in the maintenance of stability and balance when performing movements with the extremities (Andersen et al, 1988), and a strong and stable trunk provides a solid foundation for the torques generated by the limbs (Behm and Anderson, 2006;Kibler et al, 2006). Among the muscle groups located in the trunk, the psoas major is the only muscle that connects the lumber spine and lower limbs (Arbanas et al, 2009) and the largest in cross-section at L4-L5 (McGill et al, 1993;Santaguida and McGill, 1995). Hence, the psoas major is apparently an important muscle that has a role in the function of both the trunk and extremities (Hanson et al, 1999).…”

Psoas as a sentinel muscle for sarcopenia: a flawed premise

“…Psoas is the main flexor of the hip and also provides postural support of the lumbar spine, sacroiliac, and hip joints. The fibre type is mixed (40% type I, 50% type IIa, and 10% type IIx) with the 60:40 predominance of fast fibres providing for psoas dynamic and postural functions 8, 9. However, as Rutter et al 7.…”

Characteristics of Stabilizer Muscles: A Systematic Review

“…51 The recruitment pattern involves the concepts of timing patterns and timing of onset; to maintain stability, the muscles should activate at the right time and sequence, 5 and recruitment patterns are modulated according to the demands placed on the lumbar spine. 53,82 Other characteristics related to joint stability reported in the literature include biomechanical characteristics (e.g., local or deep muscles that have their origin and insertion close to a joint, short moment arms 78,79 ) and anatomical/physiological characteristics (e.g., high proportion of type I fibres, large PCSA 29,79 ). However, these characteristics were less often reported and the articles rarely provided supporting evidence for them.…”