So I'm trying to learn to play That Was Just Your Life, and I find that the fast main riff sounds best with downstrums on the non-triplet notes. I can do this fine for a few seconds, but by the time I reach the less-notes part of the riff my left arm from the elbow down is ready to give out. I have this same exact problem with a lot of Master of Puppets. Any good ways to help cause less arm pain from extended downstrumming?

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keep playing them.. you'll get stronger eventually
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I was going to say wank more.

But just keep practicing, eventually you'll get there and ask yourself why did I ever have trouble with this
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Focus on down stroking when you're practicing.

Stretch first then maybe just play the second riff to master of puppets for about 2-3 minutes straight, take a break, stretch your hands, repeat. When you're done playing either soak your hands in cold water or get an ice pack and put it on there.

Athletes always do a cool-down phase after a hard workout, they do it for a reason.
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