Dowsing/Muscle testing is really just a way to check what you actually believe and affirm it. Your own personal belief meter that shows you obviously/overtly/physically what you might only think about subtly/shallowly or the back of your mind.
How "reliable" or "where" that belief comes from is not scientifically provable or unprovable, however even a stopped clock is right twice a day. Which is more than can be said for DRs trying to treat chronic parasitism ;)
As for proof, that's what ends up killed and flushed down the toilet from time to time.