Although the hip flexors
are the prime movers in the Captain's Chair Exercise
(hanging leg lift), the abdominals are still contracting in this exercise. During this movement, rectus abdominis
contracts statically (without movement) and helps rotate and stabilizing the pelvis. In many cases the rectus abdominis is maximally contracted to stabilize the pelvis while you lift the legs toward the chest. This exercise is generally done with bent knees. Performing this exercise with straight legs creates a tremendous load on the lumbar spine and is only recommended for very fit athletes.