dumbbell preacher curl over exercise ball

Sit on an exercise ball with your feet flat on the ground and your back straight. Hold a dumbbell in one hand with an underhand grip, resting your elbow on the exercise ball. Keeping your upper arm stationary, exhale and curl the dumbbell up towards your shoulder. Pause for a moment at the top, then inhale and slowly lower the dumbbell back to the starting position. Repeat for the desired number of repetitions, then switch arms.