You ran your loop in record time, but before you sit down and back in the glory, take a walk. Doing an activity at a lower intensity helps your heart, lungs, and blood flow return to their normal state. "If you abruptly stop moving, blood pools in the muscles you were using, which can cause dizziness and fainting," says Allan Goldfarb, Ph.D., an exercise physiologist at the University of North Carolina in Greensboro. To cool down, spend five to 10 minutes (depending on how intense your workout was) exercising at a rate of perceived exertion, or RPE*, of 3. Then stretch, holding each move for 10 to 30 seconds. (If you ended your workout with strength training, just stretch.) Now give yourself that pat on the back.

*The Rate of Perceived Exertion (RPE)
Use the RPE scale to estimate the intensity of your workout session.
Here's how the four levels are defined.
RPE 3-4 Easy to moderate; you should be able to maintain this level and carry on a conversation with minimal effort.
RPE 5-6 Moderate; you can maintain this level and have a conversation with some effort.
RPE 7-8 Difficult; maintaining this level and having a conversation requires quite a bit of effort.
RPE 8-9 Peak effort; you won't be able to maintain this level for more than 3-4 minutes; no-talking zone.