Some research apparently has shown that testosterone improves collagen synth at very low doses (I think up to 200mg/wk), but does the opposite at higher doses. Deca, primo and anavar are said to help joints, but other than deca I haven't seen any independent studies to prove it. And even with deca it seems to be mostly "bro knowledge," but across the board just about everyone agrees that it helps. HGH is supposed to be the most effective at regenerating connective tissue though.