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Nope, you don't go up or down when you do a plank.

With this one, you go down an inch at a time, and then hold it there until your arms are shaking. Several minute long pauses should have the desired effect.

I don't do planks, I tend to turn everything into a resistance exercise. So what I do is get into the plank position ten times. I've even put weight on my back while doing it. Just do a plank and go up and down.