Now, I’m not exactly an expert. But in the years I’ve been at it I will say I avoid cold showers on days I do a routine. Heat helps. Cold inhibits. Basic PE rules as far as stiff tissue. Same for any exercise really.
Cold is a biological trigger to turtle for warmth. Same reason you have more trouble urinating outdoors in cold winter weather as opposed to summer.
But if cold kept you from gaining no one would ever gain in the winter time.
So my recommendation is avoid cold showers after a routine. And if you want my super smart insight, take one before your routine. Just add extra heat before you start.
If you don’t use heat in your routine don’t take a cold shower on a PE day. That’s my best recommendation in that case.