Just saw a Norwegian TV program about back pain. According to it, in most cases the reason for that pain remains a mystery.
One new hypothesis is that the 60 - 70 muscles in the lower back must work in synchrony, otherwise back pain might be a result. A while back got the worst BP in several years. Nothing of my usual "remedies" seemed to help. So decided to try YF, although don't do it regularly, it being a way too strong technique for a gynophobic Ass (Asperger) like myself. Was extremely amazed when after about 5 mins of YF, even without almost any physical movement, the pain was all but gone! Please, use yer imagination: the above hypothesis might explain, why YF could be that effective!?