I've never had a problem with arthritis (yet!) or repetitive injuries from knitting or crochet. It just hasn't happened. But I think I'm on the verge....my right hand and wrist is aching, as I type. Why? that is an excellent question! Because of the colorwork I've been doing. Here's the pic:
I did all of the lower bit, below the green and white braid, today. And, that's with yarn held in both hands. My right hand is not accustomed to holding the yarn, and it's not happy about the motions I use to throw the yarn, either. Hopefully it feels better tomorrow, or I may be taking a break from the christmas presents and working on a pair of socks.