Have you seen those "Swiss half balls" or Bosu balls? They are used for balance. Place your feet on the inflated side. They can be about four inches apart. Small muscle fibers in your core muscles of the abdomen and back will be triggered for balance. You can do arms exercises such as biceps curls while improving your balance and training your core muscles. If you do the same exercises with the flat part of the Bosu ball on top, it is even harder. The same holds true for push-ups. Little shoulder muscle fibers will be used that would not be used or used as much without the Bosu ball.
To use if further to improve balance, use either side for ballet moves such as raising one leg at a time to the front, side, diagonally or back.
Disclaimer: None of the above information can be taken as a substitute for advice from a medical professional such as a physician.
My third book, Pocket Guide to Fitness, is available on www.louizapatsis.com, http://www.authorhouse.com, www.bn.com and http://www.amazon.com. If you look up my name on those Web sites, you will find my other books The Boy in a Wheelchair and Life, Work and Play: Poems and Short Stories.