My understanding is:
Resistance training causes your body to send out a signal(not trying to get to in depth here) that reduces blood flow (vasoconstriction) to non working muscles, and simultaneously promotes blood flow (vasodilates) to the targeted muscle group being worked in order to supply the muscle with more blood for work being performed.
Why are preworkout supps that promote full body vasodilation so highly thought of if they are only working against what your body is trying to promote?
Let me know if i need to explain my point further due to poor wording. Thanks for feedback
Thread: Pre workout vasodilators