Author(s): KIJIMA, K., SAWADA, T., YAMADA, K., KITANO, Y., ITO, A., ISHIKAWA, M., Institution: OSAKA UNIVERSITY OF HEALTH AND SPORT SCIENCES, Country: JAPAN, Abstract-ID: 498

INTRODUCTION:
During maximal sprinting, the movements of the hip joint and pelvis during the ground contact phase are crucial for achieving high running speeds. The psoas major, one of the muscles contributing to these movements, has been reported to be larger in sprinters than in athletes from other athletic disciplines. Previous studies have employed magnetic resonance imaging (MRI) to assess the cross-sectional area (CSA) of the psoas major. However, MRI presents several limitations related to measurement environments and scanning conditions. In contrast, ultrasound imaging imposes fewer practical constraints and allows for relatively straightforward, non-invasive evaluation of muscle morphology in sprinters. The purpose of this study was to examine the CSA of the psoas major muscles in sprinters using ultrasound and to investigate its relationship with sprint performance.
METHODS:
Forty male sprinters (age: 20.3 ± 1.1 years; personal best 100-m times: 10.28-11.89 s) participated in this study. Participants were positioned in a relaxed lateral recumbent position on a treatment bed. The psoas major at the superior border of the iliac crest (Jacobi line) was imaged bilaterally using an ultrasound device (α10, Hitachi Aloka Medical, Japan; 52 fps). Anatomical CSA was calculated using ImageJ (version 1.54, NIH, USA). To determine relative CSA, the trunk was approximated as an ellipse and the trunk CSA was estimated. The mediolateral axis (a) and anteroposterior axis (b) were measured using a Martin anthropometer, and trunk area was calculated as S = π a b/4.
RESULTS:
The mean CSA of the psoas major muscle was 1822 ± 321 mm2 on the right side and 1862 ± 343 mm2 on the left side, with no significant bilateral difference. The relative CSA values were 5.10 ± 0.93 % on the right side and 5.22 ± 1.00 % on the left side. The total CSA of the psoas major muscles, both in absolute values and relative to trunk size, was significantly associated with a reduction in the 100-m personal best time (r = -0.475, p < 0.01; r = -0.363, p < 0.05, respectively).
CONCLUSION:
As sprinting is characterized by relatively symmetrical lower limb movements, no significant difference was observed in the CSA of the psoas major muscles between the right and left sides. Faster sprinters tended to have larger psoas major muscles, likely attributable to the substantial hip flexion torque generated during the late stance phase. Furthermore, the psoas major also contributes to hip external rotation. The repeated loading during the stance phase, involving high ground reaction forces and rotational demands, may have promoted muscular adaptation and hypertrophy.