I get cramped up when I start with some fast pulloff/open string arpeggios........sort of like the EVH finger tapping thing except no tapping. Randy Rhoads liked to do this.
i.e. on the little E - 8 po 5 po 0 (repeat 8X) 7 po 4 po 0 (repeat, etc).
You have to fret the notes pretty cleanly.
Spreading your hand across four frets low on the board and pulling the strings real quickly starts to hurt.