Well for me my muscles get painful due to nerves continually turning them off and on, causing tension sort of like cramp I suppose, but basically all over. Relieving that tension helps the pain, it won't fix it due to my nerves being messed up but at least it's some relief and will hopefully delay any increase in the painkillers.
God when she was doing it it hurt so much I don't know how to put it. But hey it's worth enduring.