Get a set of those Chinese Iron Balls the Kung Fu guys use. They come in different sizes so you can find the ones that fit your hand best. A little larger is better than too small, because you want to be able to apply enough pressure and have enough surface area to massage your tendons. Do about 5 minutes in each hand, rotating both directions. I find they're most effective to warm down and remove stiffness/cramping after playing, but they could also be used to warm up. Works wonders.
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AKR
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