And even with all this, it still doesn t have to take long to be effective. The recommendation to warm up prior to stretching is based on the fact that you should never stretch a cold muscle. Imagine trying to stretch a cold piece of taffy. You can t, and if you continue to try, it may break. But if you warm up the taffy, it becomes pliable and easier to stretch.
Muscles behave much the same way.
When warm, they become more flexible and less susceptible to injury from either stretching or exertion. As long as your muscle isn t cold, stretching can be done any time, and your body benefits even from casual stretching. The intensity of the stretch should be adjusted depending on how warm the muscle is. After a run, when the blood is pumping and the body is generating heat, the muscles will be more flexible and easier to lengthen. Now stretching can be slightly more aggressive.