My physical therapist turned me on to using a lacrosse ball to work through the knots in my muscles. Previously I had a TP MassageBall and both their rollers. I still love my rollers, but I was feeling that the ball was a bit too soft. When I really put pressure on it, it would collapse in too much and not get into deep knots.
Then, per my physical therapist's suggestion, I bought a lacrosse ball and it worked great! The firmness of the ball was perfect, but it also had some give so it wasn't like driving a solid sphere into my muscles.
This morning I had some knots in my left back and also in my pilformis and right hamstring. This is consistent with my current issues with the associated kinetic chain. Using some techniques from both the Trigger Point site and from my physical therapist, I worked on my knots there and the pain and tightness diminished or just went away.
For example, for my hamstring, I will sit on a chair and put the lacrosse ball underneath my leg, applying pressure on it by sitting on it. Then I will extend my leg slowly to pull my muscles across the pressure of the lacrosse ball. I then move the ball down my hamstring to work the entire area.
For my back, I sit in the same chair and put the ball between the chair back and my back's affected area. I lean back against the ball to apply pressure. Then I move my arm up and down to, again, move the muscle underneath the pressure of the ball. I then move the ball again over the entire area work on knots up and down my back, along my lats, my traps also.