how to get the user of an ipo?

I’m iterating the ipos with Ipo.Get() and then I would like to know which bone is using it. I see the ipo.users attribute but it returns me an int (currently 1 for each ipo), and I do not see any ipo attribute that could return me a string that could be the name of the bone.

So how can I make the association between a bone and its ipo?

thanks in advance