This thing is great. I'm using it for hamstring adhesions & tightness around the ischial tuberosity ("sit bone"). I sit on it in my desk chair. The large size works well if you're beefy. Lol It's diameter is big enough to get through a fat thigh to knead to the muscles underneath. While Dr Joe uses the smallest ball in his videos, I knew that wouldn't do a thing on my body. (If you're going to use it on a firmer surface than a desk chair, and you're overweight like me, the medium-sized ball might work fine.) I think this max size would also work well on your back while standing against a wall.
The max ball is a bit bigger than a tennis ball, just over 3" (~8cm) at its greatest diameter, point to point. The points average about 3/4 - 1" (2.5 - 3cm) deep.
It is made of smooth & dry grippy silicone, not that weird glistening, sticky stuff.
The ball itself is very firm, tho there's a bit of give due to the silicone. It's firm and unsquishable, not hard and rigid.
