Hook feet under foot or ankle brace and lie supine on incline bench with hips and knees bent. Place hands behind neck.
Flex and twist waist to one direction while raising torso from bench by bending hips. Return until back of shoulders contact padded incline board. Repeat to opposite side alternating twists.
Certain individuals may need to keep their neck in neutral position with space between their chin and sternum. If no knee support is built in to incline board, ball can be placed under legs. If upper back does not come completely down at end of movement, abdominal muscles may only be isometrically involved in exercise. Pectineus, Adductor Longus, and Brevis do not assist in hip flexion since hips are already initially bent. Knee flexors may be involved as stabilizers if incline is steep and no calf support is used. See Spot Reduction Myth.
Movement can be made easier by lowering incline, performing movement on horizontal surface, or placing arms further down away from head.
Exercise can be made more challenging by placing hands further up on head or beyond head. See Arm Position During Waist Exercises. Exercise can also be performed on higher incline board or with additional weight.