The Rock-Solid-Abs Workout - Abs Workout,The plank is one of the best exercises for a flat, toned stomach because it works all the muscles in your core, including the rectus abdominus. - Abs and cardio at the same time?
Don't let the sweet name fool you, this move works the abs quite thoroughly. Lie on your back with your knees open and the soles of your feet together (in a butterfly position). Lengthen your arms overhead so they are resting on the floor.