This move works your deep abs to flatten your stomach.
Front plank: Start on all fours. Now, keeping your back straight and your abs pulled in tight, drop down to your forearms and extend your legs behind you into a plank position. Hold for 30 to 60 seconds. You should be resting on the balls of your feet and your forearms, keeping your back straight, elbows under shoulders, your hips up. Relax your neck. This move will strengthen your transverse abdominals, the deepest layer of abs, to give your core a flat look.