Position the exercise ball in the middle of an open space with at least 6 feet of open area on all sides.
Place the dumbbells on the floor about 1 foot away from the exercise ball where you can easily grab them as you lie on the exercise ball.
Lay on the exercise ball face down with your torso contacting the top of the ball, your legs extending straight out behind you and your toes touching the floor. Position your hips and your chest on the exercise ball with your arms extending just past the ball.
Extend your arms out straight holding the dumbbells so your fingers face up with your elbow resting on the ball. When your arms extend fully, they should be at a 45-degree angle to the floor.
Bend your arms simultaneously at the elbows to bring the dumbbells toward you, stopping when the dumbbells reach almost to your shoulders.
Extend your arms out straight again to the starting point, and continue repeating this motion to perform the preacher curls.
Count the repetitions you make, striving for at least 12 repetitions before resting. Perform three sets of 12 repetitions for optimal benefit.