Lie supine on mat or bench with hips bent and feet on floor or bench. Hook feet under foot brace or secure low overhang if required to keep feet down. Extend arms down to sides..
Raise torso from mat or bench by bending waist and hips. Extend hands toward sides of heels. Return until back of shoulders contact mat or bench. Repeat.
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. See Spot Reduction Myth. Also see Dangerous Exercise Essay.
Movement can be made easier by performing movement on decline board.
Exercise can be made more challenging by crossing arms on chest. See Arm Position During Waist Exercises.