Protection against nerve and tendon damage to fingers and thumbs

Jun 28, 2015
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Ireland
I'm playing bass in a band. I also play guitar and have been playing both for about 25 years. I'm 40 now. I have found that in the last couple of years, I've been feeling the odd bit of pain in some of my fingers, particularly, my left index finger (the first section where it leaves the hand and to a lesser extent, my left thumb (also where it leaves my hand). I started noticing this shortly after I purchased 2 new guitars, a fender precision and a fender tele.
The fender had a slim neck and my left index finger would often press into the "sharp" bottom edge of the neck when playing. It got so bad, that I replaced it with a maple regular "C" shaped neck and the problem lessened.
I think my playing style might be part of the problem. I tend to have my left thumb kind of hang over the top of the neck a lot. I guess I never really learned to rest my thumb on the back of the neck from day one, like you're supposed to, so I can't really see myself changing this at this stage.
Anyway, I'm just wondering, is there some way to protect against this kind of pain? using plasters on fingers/thumbs or some kind of fingerless glove? (I'm not sure I'd like my finger tips covered).
Also, are there vitamin supplements or something similar that can strengthen tendon, nerves, ligaments. My mum suggested cod liver oil.
I use flatwounds on my P Bass as I feel they provide for smoother sliding, but sometimes they feel a bit sticky or something, less smooth, like there's resistance of some kind on them, like dirt or something else. It's usually fine at home, just seems to happen in dark cold rehearsal spaces. Is there a way to prevent this from happening? A lot of questions, I know...
Any advice greatly appreciated.