Dumbbell one arm fly on exercise ball

Sit on an exercise ball with a dumbbell in one hand and your feet flat on the ground. Walk your feet forward and roll your body down until your upper back is resting on the exercise ball. Extend your arm with the dumbbell straight up above your chest, palm facing inwards. Slowly lower the dumbbell out to the side, keeping a slight bend in your elbow. Pause for a moment, then squeeze your chest muscles to bring the dumbbell back to the starting position. Repeat for the desired number of repetitions, then switch arms.