ABSTRACT
In the present study, we examined the sex-related differences and cross-sectional age-related changes in the cross-sectional area of the psoas major muscle. The cross-sectional area was corrected for fat-free mass (FFM-corrected), which was calculated as the 2/3rd power of the total fat-free mass. A total of 240 adults (114 men, 126 women, age: 20-81 years) were included in the study. The cross-sectional area of the psoas major muscle was measured by 0.2T magnetic resonance imaging (MRI), and the total fat-free mass was measured by air displacement plethysmography. We demonstrated that the FFM-corrected cross-sectional area of the psoas major muscle was greater in males than females across all age groups. Furthermore, we examined the mean FFM-corrected cross-sectional area of the psoas major muscle across different age groups and demonstrated that it decreased with age. Our findings, when combined with previous results, show a peak in the 20s, which declined with age. Our study revealed sex-related differences and cross-sectional age-related changes in the FFM-corrected cross-sectional area of the psoas major muscle. Our findings also suggest that it is important to define reference values and ranges that take into account age- and sex-related differences when assessing the psoas major muscle by FFM-corrected cross-sectional area.
ABSTRACT
The aim of the study was to measure the cross-sectional area of the psoas major muscle (P-ACSA) in high school athletes and to produce a P-ACSA index independent of body size using an allometric modeling approach to examine the differences in gender and sport specialization. The subjects were 254 female (16.8±0.8 yrs) and 540 male (16.9±0.8 yrs) high-level high school athletes from 17 different sports. Fat-free mass (FFM) was measured by the Bod Pod system (LMI) and P-ACSA was determined by magnetic resonance imaging at the center of the L4-L5 transverse level. Since the power function model fit the data better than a simple linear model in the correlation between FFM and P-ACSA, and the power exponent parameter was almost equal to the theoretically anticipated 2/3 in both genders, the P-ACSA per FFM<sup>2/3</sup> as well as the absolute P-ACSA was calculated. Both of the absolute P-ACSA and P-ACSA per FFM<sup>2/3</sup> were significantly different according to gender and the sport specialization. While volleyball and badminton players and canoeists showed smaller P-ACSA, in accordance with the previous studies on senior sprinters, high school sprinters also showed predominant development of P-ACSA regardless of gender. These results suggested that regular involvement in sprinting activity could affect the size of the psoas major muscle in high school athletes.