"I don't believe in it. You ever seen a lion limber up before taking down a gazelle?"
Sorry, couldn't resist.
I love that quote. Jack LaLanne is DA MAN.
When I worked in the construction business, we "warmed up" by moving heavy lumber around. For me, "breathing" is the true warm up. It is the first thing I do - several nice deep breathing exercises to get the blood flowing to all body parts. Cramping/tight muscles need heat and/or massage therapy - not stretching.