When you perform aerobic exercise at a moderately high intensity you increase your metabolism, which is what triggers effective fat loss. How do you do that? Aim to work out at your optimal cardio intensity—also known as "the zone." My favorite approach for finding the zone is perceived exertion. I've found it works well with the majority of my clients, no matter their current fitness level.
Here, you simply rate your overall intensity level on a scale of zero to 10—zero being how you feel at rest, and 10 an exertion level so intense you can only maintain it for a moment. Perceived exertion is based primarily on your breathing, which becomes elevated as your oxygen needs increase. This provides a quick gauge of your intensity level. Work harder, you need more oxygen, thus, you breathe more rapidly.