Alterations in pelvic kinematics with speed, incline, and fatigue in female runners.

Introduction: In running, female runners show higher overuse-injury rates, partly due to sex-specific anatomy and biomechanics. Pelvic motion is central to lower-limb kinematics, however, female-specific responses are underexamined. This study tested how running speed, incline, and fatigue influence pelvic rotation, tilt, and obliquity in recreational female runners. Methods: Twenty-two females completed treadmill trials at 10, 12, and 14 km/h on level ground and at 10 km/h with 5% and 10% inclines, before and after a 30-minute run at 80% heart-rate reserve to induce moderate fatigue. A 3D motion-capture system recorded pelvic rotation, tilt, and obliquity at heel-strike, toe-off, peak values, and ranges of motion. Linear mixed-effects models assessed main and interaction effects; asymmetry was quantified via symmetry index between left and right gait cycles. Results: Higher speeds increased peak pelvic rotation, tilt, and obliquity, and enlarged rotation and obliquity range of motion. A 10% incline raised peak pelvic obliquity and rotation and increased range of motion for rotation, tilt, and obliquity; a 5% incline had no measurable effect. Fatigue increased peak pelvic rotation and range of motion for rotation and tilt. A fatigue × 10% incline interaction showed that incline-related increases in tilt range of motion observed when fresh were reduced under fatigue. Pelvic tilt asymmetry rose with speed. Discussion: Speed, incline, and fatigue each modulate pelvic kinematics in recreational female runners, with effect sizes often exceeding reports from mixed-sex samples. Notably, greater frontal-plane motion at higher speeds and increased transverse-plane motion with incline and fatigue may heighten loads on the iliotibial band, hamstrings, or lumbar spine.