As musician and athlete, I regularly use (10mins / day) my power ball to beef up my whole arm and fingers.
It runs very fast, it's fun between friends with a very strong addiction from the first minutes.
For more fun, try early on not to use string, it will make you less to remove it (to help roll your power ball along your leg down, and when she did a little light made of light and fast rotations that will decrease to a lot of speed)
Good run!
