Most trainers think muscle, joint, ligament and bone in that order… but when training the ABS, be it static plank or a dynamic exercise like a roll-up or pilates move, there is a contraction of the rectus. The diaphragm muscle, the main breathing muscle of the body works with the abdominal muscles. Remember this, when to breath, how to breath and how to stretch the diaphragm after training the abs and vice versa after training the aerobic or anaerobic systems.