Interesting.

Once, after suffering a 'charley horse' (a severe cramp) in my upper thigh, I was told by my doctor to put a cupful or two (I've forgotten) of cider vinegar in bath water and soak my leg. He said that cider vinegar is a muscle relaxant. I've never heard that anywhere else.

I wonder if vinegar-soaked compresses applied over aching joints would help?