Place feet under foot bar or low overhanging stationary object. Lie supine on floor, mat, or sit-up bench with hips and knees bent. Cross arms on chest.
Flex and twist waist to one direction while raising torso from bench by bending hips. Return until back of shoulders contact floor or mat. Repeat to opposite side alternating twists.
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.
Movement can be made easier by placing arms further down away from head. Exercise can also be performed on declined bench.
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 incline board or with additional weight.