Grasp stirrup and sit on stability ball with side facing low cable pulley. Roll body down and lie with back on ball, hips nearly straight, and feet apart on floor. Hold onto stirrup with both hands with arms extending straight upward.
Allow resistance from cable to turn torso downward, toward direction of pulley while keeping arms straight and perpendicular to torso throughout movement. Pull stirrup in an arch over shoulders by rotating torso to opposite direction of pulley until cable makes contact with shoulder. Return to original position in opposite direction and repeat. Continue with opposite side.
Both arms should be kept straight and perpendicular to torso. Hips should also be kept nearly straight, only slightly bent. Also see other view.
This movement involves both spinal rotation and hip external rotation. Because leg furthest from pulley acts to counter weight of cable's resistance, greatest downward force onto floor is place on foot closest to pulley. Since foot of near leg provides more secured base of support, external rotation of near hip provides significantly more torque as compared to relatively passive internal rotation of far hip.
Continued rotation would occur through spine except when cable makes contact with body precluding further movement and resistance would no longer be provided through cable since line of force is no longer perpendicular line of pull. Seated oblique exercises or those exercises where hips are stabilized, allow for greater range of movement through spine. See Spot Reduction Myth.