I've wondered to what extent the "warming up" was going on in my hands and muscles. Subjectively, and that's good enough for me for now, it sure seems to be the mostly the bass that's changing, the strings, or both. In any case, what I experience is that pizz. playing feels less stiff and the entire instrument just seems to respond more easily after extended long-note arco.
I'd already been playing pizz for 45 minutes or so, so I was warmed up. And the pizz was immediately looser after this and it seems unlikely that the strings would change in any way...but...
