Place weight between ankles or use no weight. Grasp and hang from high bar.
With knees straight, raise legs by flexing hips until thighs are just past parallel to floor. Return until hips are extended downward. 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; see Weighted Hanging Leg-Hip Raise.
Exercise can be performed without added weight until more resistance is needed; see Hanging Straight Leg Raise. Knees can flex along with hips to decrease intensity; see Weighted Hanging Leg Raise. Also see Spot Reduction Myth and Lower Ab Myth.