This exercise works all abs muscles. Due to the ball instability, additional stabilizer muscles are involved in the workout.
Lie on the exercise ball with your lower back pressed against the spherical surface of the ball.
Legs are bent and pressed firmly against the floor.
The upper torso should be hanging off the top of the ball.
Place your arms behind the head or cross them on the top of your chest.
As you inhale, flex the waist by contracting the abdominals and curl the shoulders and abdomen upward until you feel a nice contraction on your abdominals (your main goal is not to fall).
Keep your neck stationary.
As you reach maximum contraction, while exhaling, lift up the upper body as if you are crunching the inside trying to bring your shoulders closer to your waist.
Reach the maximum contraction of the abs, hold this position for 2-5 seconds and slowly return to the starting position.
Don't sit on the ball during the exercise and don't move your lower back.
To keep your neck stationary, imagine that you are holding a small ball with your chin.
If the exercise is too easy for you, you can hold a dumbbell or a barbell plate over your head.
To get a better foothold, you can place them against the wall or behind a machine.