Hi, I'm Denise Druce for LIVESTRONG.com. Let's look at three great exercises you can use with a core ball to flatten your stomach. For crunches on the ball, start by sitting on the ball with feet hip distance apart and then walk your hips down. Bring your hands to the back of your head and lift and lower. So you are trying to keep your elbows wide and every time you lift, exhale, pull your navel to your spine. It's important that you don't push the muscles out but that you pull them in instead. If you want to make that a little more challenging, come in closer to the ball with your feet, lay with your body a little more flat and lift and lower there. Let's look at some oblique crunches using a core ball. So lower your hips down, bring your fists up underneath your chin. This is kind of like a boxer move. We're going to take the elbow down toward the mid-line of the body. So in addition to a crunch now, you are also working your obliques, side to side. To do a plank on the ball, bring the ball in front of you, you can start on your knees, come down to your elbows and then extend one leg and then the other tucking your toes under. The cool thing about a ball is you can move the ball around a little bit to make the exercise more challenging. These are ideas for how to flatten your stomach using a core ball. I'm Denise Druce for LIVESTRONG.com.