In a standing position, lean against the ball where it is supporting your back. Be sure to be leaning against a wall or some other solid structure.
While leaning against the ball, your body should be in a vertical position. In each hand, hold a dumbbell down at your sides, fully extended.
With palms facing out, curl the weights up to your shoulder. Pause for 1-2 seconds, contract the muscle and lower back down slowly.
During the entire exercise, keep your back flat and body still, this way of the tension is placed on your biceps.