Many years ago when I worked as an electrician in Local #358 I saw an older gentleman spraying WD-40 on his hands and working in into his fingers and knuckle joints. Being the inqusitive type I moseyed on over to this gent and asked him why in the world he was using WD-40 on his hands. He said “kid this stuff is good for my arthritis”. At the time I thought he was nuts (he probably was, but not because of the WD-40!). Fast forward many years later and I’m playing about 100 gigs per year and working in my repair shop using my hands all day plus playing guitar testing all the repairs and custom builds I was doing. My hands were hurting a little and stiffening up while not in use. I remembered this guy and tried the WD-40. It worked! It instantly reduced the pain and loosened up the knuckles and joints!
Mind you this is not a cure because I believe Active Release Techniques, systemic enzyme supplements and hand strengthening with clubbells are more effective for overall hand health but for a quick fix next time your hands are hurting and/or stiff try a little WD-40!