Obviously the Gift that keeps on Giving

You know when you buy your sister a really cute necklace because you know you will get some use out of it too?  Well, this is pretty much the same, only apply it to men.  Now, boyfriends and husbands of the world have a way to help tone and sculpt their ladies forearms and biceps.  But, it seems there may also be a beneficial factor in it for the guys as well.  Fast foward to the 40 second mark to see how they explain "Dynamic Inertia."  Although I'm pretty sure the rest of the world calls is something else.