Or, at least, it is just too difficult to find one that is not embarrassing. So, I will tell you how I've been doing it for whatever that's worth.

You will need a loving assistant. Someone who will indulge this latest quirk. Stand facing one another just under an arm's length apart. Now, you extend your non-dominant arm out to the side and slightly swept forward. Your partner places his corresponding hand lightly over your extended elbow and his other hand on your opposite shoulder where the arm hangs down at your side. Calmly take a breath and, with the intent in your mind of conveying a "yes" response, exhale as you give a quick nod. This is the signal for your partner to deliver a single, sharp downward push and release force to the extended arm. This is a sort of calibration so that you know what a "yes" is.

Now, with your other arm, hold your sample against your solar plexus and repeat the procedure with the "yes" intent replaced by an "inquisitive" intent. Your partner should try to reproduce his action as exactly as possible and not use excess force. You are looking for changes not training for the Olympics.

Many things will match your "baseline" with no problem. But, some things will surprise you and the weakness will be unmistakable. Spooky.