I get discomfort when using the index finger of my left hand between the knuckle and the first joint (I believe that is the metacarpal)
If I give it a rest (from guitar playing) it eases.
Are there any exercises I can do to strengthen the area or types of massage that will keep this from recurring?
There is no pain in the joint itself or obvious inflammation (though there must surely be some if it hurts to touch or to use)
For guitarists this is the finger that frets C in the C major chord in standard tuning.