Place weight between ankles or use no weight. Grasp and hang from high bar.
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. Exercise may be performed with ab straps. 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. Knees may be kept extended throughout leg raise to increase intensity; see Weighted Hanging Straight Leg Raise. Also see Spot Reduction Myth and Lower Ab Myth.