When performed properly, the kettlebell swing works the abdominals in conjunction with the other 600 or so muscles it recruits. There is a way, however, to maximize the move’s six-pack building potential. This secret lies in how we hold plank position.
A rookie mistake when performing the kettlebell swing is to simply hinge at the lower back while rocking backwards and forwards. While you may burn some calories this way and develop some delayed-onset muscle soreness (DOMS) making you think you achieved a great workout, you also put yourself at risk of injury. Even when using the correct form of hinging at the hips and driving them forward while maintaining a neutral spine, you can do a little more to engage the abdominals and strengthen your core.
Think of the top of the swing as the same configuration as holding plank. In that push forward of the hips to stand tall, also brace your core as you energetically pull your pelvis up toward your ribs. This is the same thing that happens when you hold a strong (and aligned) plank.