Note that for acupuncture on pain relief, it seems that the perception of it working is that in some instances it makes people aware of muscles in questions.

So essentially, it's the same as telling people to sit up straight and don't slouch, just buried under the ceremony of needle sticking.

Reminds me of a cartoon I saw while little. Where a clever child monk figures out that a king's back pain disappeared not because of the really expensive mythical ceremony he keeps paying for, but because he rode a horse on the way there and the exercise from horse riding was what relieved the pain.