Ok, so you have your cardio down to a science: You know when, where, how long and how hard you have to work to get that feeling of pure adrenaline – when you know you’re taking your body to that next level of lean. But are you really in the zone? Although many experts dismiss the notion of a “fat-burning” zone, some studies show that in order to maximize fat loss, you must first reach your “fat burning zone.” That zone is defined as 35 to 69 percent of your maximum heart rate (MHR).

To get started, here’s how to calculate your MHR.

As soon as you wake up, find your resting heart rate (RHR): Feel your pulse by pressing into your left wrist with your right index and middle fingers. Time yourself for 15 seconds, counting the beats of your pulse; multiply that number by four. This is your resting heart rate. Write it down.

Using your RHR, follow this simple formula to find your MHR and fat burning zone: 220 – age = MHR – RHR x .65 + RHR = 65 percent of MHR (ok, ok, here’s the breakdown)