That's kinda what I mean, you need to do those situps, which still provide resistence, rather than take the latest shortcut trend. I'm sure the balls help for a few things, but adding them to any random exercise like db shoulder presses, bench, or curls (seriously) seems like a way to do nothing more than gimp that exercise. Balancing takes practice, but I'm curious if that's more muscle memory than muscle development, know what I mean?