It has been known for a long time, but people don’t change their beliefs easily. You stretch AFTER you exercise the muscle, not before. Stretching before can lead to injury and also weakens the muscles you are about to use (temporarily). Stretch after the exercise to reduce the pain (the good pain) or possible spasms or cramps that may catch up to you later.
Before exercising warm up. Quick waling, running, that sort of thing. Don’t stretch.
I know that you either already knew this or you simply don’t believe me. I can’t help you if you fall into the latter category. But you can always read about it (well, at least part of it) in the New York Times. (You may have to log in.)