dunno about grinders, but you might check your local library's interlibrary book loan system for a book entitled "Trigger Point Massage Therapy", by a man named Claire Davies, IIRC. Taking his advice really helped my carpal tunnel symptoms. it's free and doesn't hurt (much) He says that on scale of 10, 1 being no pain at all, and 10 being unbearable, you should massage at about a pain rating of 7-8, for a few seconds on a given muscle group.
You can can then either work on another muscle group, or go do something else, and come back to the one that was hurting too much. it might take a couple of weeks of several times per day massage, or you might get relief almost instantly, like I did. what it does is show you how to "smash" the belly of the muscle between say, your elbow, or a hard rubber ball and the bone under said muscle, releasing tiny cramps (which add up) caused by lactic acid, muscle spasms/overwork. you try not to use your fingers much, cause you'll ruin your hands if you do. You try to use your heel, knee, or one hand supporting the other (he shows you how to shape the specific hand "tools") and save your fingers. This is not "feel good' swedish massage. This is deep, heavy duty therapy. Often, the muscle that's causing the problem is far from where you "feel" the pain. For instance, carpal tunnel is often caused by neck muscle spasms, which pinch off the nerves where they emerge from the spine, to go down your arm. Many doctors are unaware of this. Others know and just want the surgery fee!
Like right now! It hangs on the wall and I rest it on my shoulders while typing.