Off topic: Kettlebells might lose their "heavy" in micro-gravity[1], but they don't lose their "massy". I first read the term "massy" in some sci-fi book, by Heinlein, I believe.
It takes more effort to overcome the inertia of an object with a lot of mass than it does to overcome the inertia of an object with less mass. So, you can still use massy objects to work out in micro-gravity! Or so I've been led to believe by convincing fiction. :)
1: I've also been led to believe that micro-gravity is a better term than zero-g for the conditions experienced during free fall.
