Tip - The Best Lower AB Exercise Crunches | LIVESTRONG.COM

The lower abs are part of the rectus abdominis. This is the main abdominal muscle. It's what you see when someone sports six-pack abs. The rectus abdominis is responsible for flexion of the spine, pulling your rib cage toward your pelvic bone, as in a crunch. Because the rectus abdominis is a long sheath of muscle, ab exercises that pull the legs...