Just like an athlete does some light stretching to get their muscles limbered up for practice or performance, you should take a couple minutes to loosen up your hands before beginning any intensive playing.
Here’s a simple and effective stretching exercise to warm-up and synchronize both hands in a short amount of time. It uses just the 1st and 4th fingers, and takes place at the 7th position. Check out the tab below:
If the stretch across that span at the 7th position is too much, just move up the neck until it feels more comfortable. Your fretting hand should stretch a little bit, but no exercise should cause acute soreness or pain. Work on groups of 4 as well as groups of 6 separately, before combinng them. As usual, start with strict down-up alternate picking, then try starting with an upstroke.