Abdominal muscles are body armour. They help protect your vital organs from damage. They keep your body performing at maximum and, when the clothes come off, they make you look terrific. This workout is the anvil where that armour is fashioned.
No-Equipment Ab Exercises Chart - Bodyweight exercises always recruit more than one muscle group for each exercise so it is impossible to isolate and work one muscle group specifically by doing one type of exercise. It is however possible to increase the