Grasp and hang from high bar with slightly wider than shoulder width overhand grip.
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 downward. Repeat.
Exercise can be performed with ab straps. 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.
Knees may be kept extended throughout leg raise to increase intensity. Alternatively, exercise can be performed with added weight. Knees can also be raise to shoulders to dynamically involve Rectus Abdominis.