If you are not familiar with Dynaflex, then you might want to checking it out. I believe that they are best known for their Gyro Exerciser, and I’m going to do my best attempt to describe what these transparent balls do.
The Gyro Exerciser have a rotor inside that you can spin with the help of some string that it comes with. Seriously, you wind up the string, yank it, and the rotor starts spinning. If it spins fast enough, there will be a glow inside. As you hold the ball in your hand, there is a tendency to move thanks to the power of spinning physics.
I believe that the object is to keep the rotor in it spinning as long as you can. That is, when you move the ball with spinning rotor in your hand, it will resist your hand’s movement. As you move your hand back and forth, you get some serious exercise for your wrist.
Yeah, it was pretty hard to describe, which is why I recommend trying it out for yourself. You can get one in turquoise or pink for about $14.95 on the Dynaflex site.