Flat Stomach Exercises

To get a flat stomach you should do some challenging exercises to work your core. Exercises like running and using an elliptical trainer can burn off belly fat, but to tighten your abs, intermediate and advanced core exercises are the way to go. Fitness expert Jeanine Detz recommends doing three sets of 15 to 20 reps of ab exercises in her book "Ultimate Core Ball Workout." She says to do approximately three ab exercises consecutively in an abdominal workout.

Trunk Rotation

The trunk rotation is done with a stability ball and a medicine ball to train the abs and obliques. The ab muscles work to stabilize your body while sitting up tall on a stability ball with your feet flat on the floor. The abs are further worked while you hold a medicine ball straight in front of you, at chest height, and rotate your torso. The rotation activates your oblique muscles, which are at the sides of your stomach. You can use a lightweight med ball, around 2 lbs., and increase the weight as your abs get stronger, recommends Thomas Boettcher in his book "Core Training for Greater Strength and Better Health."

Leg Raises

Leg raises are an exercises suitable for elite athletes, according to Boettcher. However, if you're not an athlete with the strength to do them correctly, you can modify them. When done properly, and without using momentum to swing your legs, you will definitely feel this exercise strengthening your abs. Leg raises may be done on a suspensory rack or a hanging bar, both of which you will likely find at a gym. The first step is to position yourself on the rack or to hang from the hanging bar. Your legs will hang straight toward the floor and you then raise them straight up to make a 90-degree angle with the body. The most advanced version is done hanging from a bar and holding a medicine ball between the ankles as extra weight.

Ball Roll-Up

The ball roll-up exercise takes a you through a range of motion for the torso even greater than when doing sit-ups. It is an exercise recommended by Detz for beginners and advanced exercisers. Beginners will do the exercise with their knees bent and feet flat on the floor and advanced exercisers will have their legs straight on the floor with their feet pointed. The ball roll-up is performed by lying on your back with a stability ball held between the palms. The starting position has the ball on the floor with the arms straight and next to the ears. You then curl your back off the floor and raise the ball straight up and over your head until it is in front of your chest. Advanced exercisers will then bend forward and reach toward the toes, allowing the lower back to round. Beginners should try to reach the ball over their knees.