Stability balls are large inflated balls which can be used to support the body to perform a wide variety of fitness exercises. While stability balls are common for working the core, they can also be used in place of a standard bench in concert with dumbbells to perform several upper body exercises.
Working out the arms with dumbbells on a balance ball engages core muscles missed on a standard bench. Exercise the arms on a balance ball using dumbbells with a certified personal trainer in this free video on fitness and resistance training.
When performing the sitting side flexions posture exercise with arms overhead, use a fitness ball and keep the hips steady to increase flexibility. Practice this posture exercise with tips from a personal trainer in this free workout video.