Relationship between Hip Strength and Trunk Motion in College Cross-Country Runners

Purpose: Hip strength may directly relate to abnormal running mechanics and contribute to the high incidence of overuse injuries in distance runners. The purpose of this study was to determine the relationship between hip isokinetic strength and thorax and pelvic motion during treadmill running. Methods: Isokinetic hip strength and treadmill running kinematics were collected on 24 collegiate cross-country runners (14 males and 10 females). Each subject completed a running protocol on a treadmill at a self-selected speed (3.58 +/- 0.26 m.s(-1)) and prescribed speed (3.58 +/- 0.0 m.s(-1)). Kinematic data were collected with retroreflective markers attached to the thorax, pelvis, and each lower extremity segment (thigh, shank, and foot). Thorax and pelvis range of motion (ROM) were calculated from initial ground contact to toe-off. Pearson correlation coefficients were used to determine the relationship between strength and ROM (P < 0.05). Differences between male and female athletes were tested with mixed-design ANOVAs (P < 0.05). Results: Isokinetic hip extension and abduction torque had significant inverse correlations to thorax axial rotation ROM during stance phase of running (r = -0.60 and r = -0.53) at self-selected speed. Frontal plane pelvic obliquity ROM was also significantly correlated to hip strength (extension r = -0.49; abduction r = -0.44). Similar correlations were found during the prescribed speed condition. Female runners had significantly decreased normalized strength (hip extension 1.8 +/- 0.4 N.m.kg(-1), P < 0.05; hip abduction 1.0 +/- 0.2 N.m.kg(-1), P < 0.05), increased pelvic obliquity (13.1 degrees +/- 2.6 degrees, P < 0.05), and thorax axial rotation (34.5 degrees +/- 7.0 degrees, P < 0.05) ROM compared to males (hip extension 2.5 +/- 0.5 N.m.kg(-1); hip abduction 1.3 +/- 0.2 N.m.kg(-1); pelvic obliquity 8.9 degrees +/- 1.9 degrees; thorax axial rotation 22.6 degrees +/- 3.5 degrees). Conclusions: Moderate correlations were found in hip extensor and hip abductor strength and pelvic and thorax motion during running in collegiate runners.