Respiratory-Pelvic-Hip Coupling

The pelvis, sacrum, and femurs function together as a kinematic system that changes with respiration. Exhalation reverses inhalation mechanics by producing posterior innominate rotation, relative sacral nutation, IPA widening, and femoral flexion, adduction, and internal rotation. During inhalation, anterior innominate rotation produces relative sacral counternutation and narrows the infrapubic angle. Inhalation normally drives the femurs into hip extension, abduction, and external rotation.