"All of the strength of the rest of the body stems from the core," he says. "It also helps as far as improving balance and flexibility and reducing injury. Having weak abs and a weak lower back is an invitation for injury."
In addition to working the abs, Raphael stresses the importance of and regular cardio exercise. Before you can achieve a flat stomach, you need to reduce overall body fat.
Here the 10 most effective abdominal exercises. Raphael suggests that beginners start with the Ab Crunch and Reverse Ab Curl.
1. Bicycle Maneuver (studies actually prove this to be one of the most effective)
Starting Position:
Lie on a mat with your lower back in a comfortable position. Put your hands on either side of your head by your ears. Bring your knees up to about a 45-degree angle. Movement:
Slowly go through a bicycle pedaling motion alternating your left elbow to your right knee, then your right elbow to your left knee.
Key Points:
This can be a more advanced exercise. Do not perform this activity if it puts any strain on your lower back. Do not pull on your head and neck during this exercise. The lower to the ground your legs bicycle, the harder your abs have to work. 
2. Ab Crunch
Starting Position:
Lie on a mat on your back. Make sure that your lower back is relaxed against the mat during this exercise. Bend your knees until your legs are at a 45-degree angle. Keep both feet on the floor. Place both hands behind your head. Movement:
Contracting the upper abs, raise your head and upper torso off the floor until your shoulders are slightly lifted. Slowly return to the starting position, stopping just short of your head touching the floor.
Key Points:
Exhale as you contract the abs. Inhale while returning to the starting position. Keep your eyes focused on the ceiling to avoid pulling with your neck. Your hands should not be used to lift the head or assist in the movement.
