Position forearms on padded parallel bars with hands on handles, and back on vertical pad.
Raise legs by flexing hips and knees until hips are completely flexed or knees are well above hips. Return until hips and knees 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 on flat surface or incline to make this exercise less intense.
Exercise can be performed with added weight or knees may be kept extended throughout leg raise to increase intensity. Knees can also be raised to shoulders to dynamically involve Rectus Abdominis.