I use the tennis ball method of massaging the SI joint area. For example, go to http://kelziebeebe.blogspot.ca/2011/06/self-massage-with-balls.html and search for the phrase “Butt and Back of the Thigh” without quotes. I find that the tennis ball gets soft very quickly, and I don’t like the variation of hardness as the tennis ball ages and gets replaced. Is there a hard-ball version of the tennis ball for physiotherapy purposes? It should be textured on the surface so that it doesn’t slip as one rolls around on it. The closest I found was a hard BASEBALL, but only texturing is the threaded seams.
From surfing the web, I ran across the idea of a lacrosse ball ( Lacrosse ball - Wikipedia ) but it might be a bit small (or my cheeks are too pudgy).
Just wanted to thank respondents. I’m finding the lacrosse ball works just fine, but good to know there are all these references to alternatives for the future.
The lacrosse ball works great for the muscle beneath the SI joint, but higher up where it’s predominantly bone, I have to resort to the tennis ball.