You need to warn up before and during practice without a guitar. I dont know how to describe these exercises, but they help. I'll try to explain:
1. Massage forearm.
2. Massage palm and fingers
3. Take one hand and gently pull the other back (hold the hand to be pulled back like you were making the "stop" sign a crossing gueard uses) lol.
4. Do the same as number 3, but point the tips of the fingers down and palm facing you.
5. Repeat 1-4 with the other hand.
I played a show 2 weeks ago and did not have time to do these excercises and by the 4th song, I was cramped almost too bad to play.
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