Bob is on to something, I think. That hammering motion brings it on more than anything else for me. When I spend too much time roughing out staves with a hatchet I am bound to flare it up again. I am no knapper, but I see that there is a lot of "hammering" type motion involved. Given a week or two of rest, mine goes away. I also found some relief through an excercise routine using a hammer. If you check on line for some videos, you might see one where a weight on a stick (or a big claw hammer) is used to stretch the forearm muscles out by rotating it back and forth with your forearm resting on a table. That little 180 degree, back and forth, stretch seems to help some. I bought one of those compression type bands that you wear on the mound of your forearm, and that seems to help some. Ibuprofen or naproxen sodium? (alieve) also helps some - but nothing helps it so much as to stop doing what is causing it for a while. It can get so bad that you can't comb your hair or tilt a cold beverage.... Good luck with it.