MUD Mired in time...

The pelvic determinant contributions are interesting. Roll, pitch, and yaw – but these perfectly appropriate terms are not used - ever. Requires a pilot’s license I suppose. Body mass, not over either leg but between them can rotate horizontally to increase the two step lengths of each stride with no anti-gravity cost. Arm swing allows the right/left/right/… alternating rotational torque to be offset (neutralized). Is that why we swing the arms? Yup. Although the hip is still riding upward and then downward even after the knee/foot tricks, the center of mass stays more level as one hip upthrusts. It simply lifts one side of the pelvis centered on the center of mass as the other side is dropping. No vertical cost.