I've been having IMS, which uses the same needles as acupuncture but operates on slightly different principles. The idea is that it gets clenched muscles to release, so if your muscles are in good shape you don't even feel the needle going in. If the muscle is tensed up or shortened, there's a really strong cramping feeling and then it relaxes. There's an overview on this website with more info: http://www.intramuscularstimulation.com/2.htmI have to say, I really don't enjoy it. I've been having it in my back and down both legs, where the muscles have been really tight and tense since my injury. Most of the needling sites produce an incredibly strong reaction - it's a pretty severe discomfort. However, it's very effective; I find that with the muscles relaxed, the pain levels really decrease afterwards. (The worst pain isn't actually from the injury site, but from the PFS in both knees.) It takes a week or so for things to start tightening up again. It's definitely not for everyone - a friend of mine stopped getting it because she couldn't stand the sensation - but I am finding it helpful for managing pain.