Adding Swiss ball, exercise ball or stability ball to your workout can allow you do a number of exercises that efficiently strengthen and tone your abdominal muscles. It can also improve your flexibility and stretch out your torso.
The ball is soft and lightweight and comes in different diameter and colour. Your height is actually what determines which size of ball you should use. Using the ball for support while toning the lower body and lifting weights will improve your balance and indirectly strengthen your abdominals.