Position forearms on padded parallel bars with hands on handles and back on convexed surface.
Raise legs by flexing hips and knees. As hips approach full flexion, lean back. Continue to raise knees toward shoulders by flexing waist and raising hips and low back from convexed surface. Return until waist, hips, and knees are extended. Repeat.
Rectus Abdominis and Obliques dynamically contract only if actual waist flexion occurs. With no waist flexion, Rectus Abdominis and External Oblique will only isometrically contract to stabilize pelvis and waist during hip flexion; see Weighted Vertical Leg Raise. It may be necessary to completely flex hips before waist flexion is possible. See Spot Reduction Myth and Lower Ab Myth.
Lie on flat surface, incline board, or exercise ball to make this movement less intense.
Exercise can be performed with added weight to increase intensity.