Hook feet under foot brace and lie supine on incline board with hips bent. Cross arms on chest.
Raise torso from bench by bending waist and hips. Raise crossed arms over knees at top. Return until back of shoulders contact incline board. Repeat.
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. Also see Dangerous Exercise Essay.
Movement can be made easier by lowering incline, performing movement on horizontal surface, or extending arms over legs.
Exercise can be made more challenging by placing hands further up near head. See Arm Position During Waist Exercises. Exercise can also be performed on higher incline board or with additional weight.