Position forearms on padded parallel bars with hands on handles, and back on vertical pad.
With knees straight, raise legs by flexing hips until thighs are just pass parallel to floor. Return until hips are extended. Repeat.
Rectus Abdominis and Obliques only contract dynamically if actual waist flexion occurs. With no waist flexion, Rectus Abdominis and External Oblique will only act to stabilize pelvis and waist during hip flexion. It may be necessary to completely flex hips before waist flexion is possible, as in leg-hip raise. Also see Spot Reduction Myth and Lower Ab Myth.
Lie back on incline board or bend knees along with hip to make this exercise less intense.
Exercise can be performed with added weight. Knees may be kept straighter throughout movement to increase intensity. Knees can also be raised to shoulders to dynamically involve Rectus Abdominis.