[Physioguy]

Hmmmm... not sure I should get into this. I have used a swiss ball myself (able to stand on it unsupported and do squats, and also tossing a 12 lb medicine ball back and forth with a training partner) I have used a swiss ball with clients, but I am leaning away from it lately. It does add some variety to the programs.

The thing is, while I think it does recruit the core somewhat (as well as all the other muscles of the body), I'm not sure it works them all that functionally. I never felt that I was particularly more "stable" after training on the ball (albeit I have decent core strength as it is) [I'm not sure quite why it got credit for being particularly a "core" exercise - I always felt the foot and ankle was working the most, followed by the thighs, then hips, and so on.]

The philosophy I adhere to would say that training with artificial instability (i.e. kneeling or standing on a swiss ball) will develop artificial stability.

Balancing on the ball is not actually all that difficult, although it IS a good trick that people seem to get a kick out of.

To my mind, the best thing that you can do for your "core" is to regularly perform trunk movements in all planes of movement, in functional positions (i.e. standing), progressing to resisted movements, holding onto weight in the form of dumbbells or medicine balls, etc. Make sure your hip and thigh musculature and joints remain flexible. Avoid doing common but mis-informed exercises which may place excessive stress or compression on the joints of the spine.

The spine is tricky - it needs some stress (active lifestyle, exercise), but too much (i.e. too heavy, to intense, poor body mechanics) and too little (inactivity) are both bad.