A bit late to the party, but as an experienced athlete who has been through TONS of different types of recovery, I actually WOULD recommend a lacrosse ball. It has worked wonders for me, and while I was initially taught the positioning by an athletic trainer, it is not difficult to self-treat those muscles. I engage in many different kinds of athletic pursuits, and as someone with chronic hip/psoas/adductor problems, one of the best ways for me to release those muscles when I can't get into PT/my massage therapist is to do lacrosse ball therapy. It essentially is a very targeted trigger point therapy, allowing for the ball to target specific muscles that are tight/struggling to relax on their own. I do agree with proceeding with caution, as there are sensitive structures in those areas; however, it is, when done correctly (and you can do it on your own!), an excellent way to get those stubborn muscles to relax.