Hello, fellow guitarists

I've got a question. It's about my speed. Let's take an example
of my 2-week period. I started with about 160-170 bpm quarter notes and got a steady improvement till 210 bpm ( for example I could play Painkiller with downstrokes, Creeping Death actually faster than actual tempo and I was practicing Indians of Anthrax). I had no problem at all.

Now when I eased with my downpicking and started to play different things again for a while, my downpicking speed has dropped drastically (From 210 to 190). I have still practiced downpicking.

Any ideas how to maintain speed without having to use all the time practicing only picking down?
This is one of the only instances where you will see me compare playing guitar to any kind of sport but in this case... it really is more of a brute muscle endurance thing than skill. Use it or lose it dude.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

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