Abstract
The purpose of the study was to evaluate functional importance of two hip flexor growth, rectus femoris (RF) and psoas major (PM), on sprinters by investigating relation between each muscle size and the joint torque and angular velocity. Subjects were 24 female and 25 male sprinters and 64 age matched volleyball players and 20 untrained students participated in the study for comparative purpose. Maximal hip flexion torque (HF) was measured by an isokinetic dynamometer (Biodex System 3) at an angular velocity of 3.14 rad/s and an index of maximal hip flexion angular velocity (HAV) was calculated by dividing knee pull-up speed (COMBI Ballistic Master) by femur length. The muscle cross-sectional area (CSA) was obtained by using magnetic resonance imaging. In sprinters, the PM size (CSA x height) showed week but significant correlation with HF (r=0.48 and 0.34 for females and males respectively) although there was no significant relation between the RF size and HF, suggesting either muscle size of the two hip flexors was not a strong determinant of HF or HAV in sprinters. When all the data were included, muscle size of the two flexors was correlated significantly with HF irrespective of gender. In addition, the PM size was still correlated significantly with HAV. There was no significant difference in the RF CSA between sprinters and volleyball players although sprinters showed significantly larger PM CSA than volleyball players whether the data were expressed in absolute or body-size relative values. HF was significantly higher in volleyball players than in sprinters, while HAV was significantly higher in sprinters than in volleyball players. The present results suggested that predominant PM growth observed in sprinters was preferable to hip angular velocity and assumed to be an adaptation in favor for sprinting performance.
