When you love to run and daylight is limited, you might feel a little pinched for time. One way people save time is skipping the cool down since it is cold outside anyway. I am here to remind you that no matter the length of your run you need to cool down. Cooling down after a run isn't really about lowering your body temperature. It is about allowing your heart rate to slow down gradually so you don't shock your cardiovascular system. When running, your heart pumps large amounts of blood to your legs and skipping a cool down means blood will pool in them, overtaxing your heart. Since one of the reasons to run is to keep your heart healthy, you don't want to end a workout leaving your heart in a lurch. So pay attention to your heart rate rather than your temperature.
A good cool down will also help reduce sore muscles. It generally requires jogging slowly for five minutes, followed by five minutes of walking. The walking will help stretch your hip flexors, too. If it is too cold outside, move the walking portion of your cool down inside. I will admit when I do this, my dog gets very confused as I pace around, but my heart and leg appreciate it.