In the past 20 years, measuring my heart rate hasn't really been on my radar. Sure, in group fitness classes, the instructor would guide me through checking my heart rate, and I've experimented with the monitors you can find on cardio machines. But honestly, grasping the metal sensors with sweaty hands is never a pleasant experience, and often it can't even find my pulse.

Still, knowing that I was going to be getting serious about weight loss this year, I invested in my first heart rate monitor. And while that sounds pretty cool, it's not so cool if the person wearing it doesn't know what the numbers mean. (Did I mention I had no idea what the numbers meant?)

Then a few weeks ago my new dietitian, Heather Wallace, suggested I enroll in the Life Time Fitness Team Weight Loss, a heart-rate-zone-based class, to get my metabolism revved up to accompany my weight training. When she mentioned the term "workout zone," I looked at her with a blank stare.

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She suggested I take a VO2 test test to understand how to best utilize my workouts by learning my zones. I did, and it's true, running my hardest on a treadmill with a mask on wasn't the most pleasant experience. But the results were revealing. I found out that these are my zones:

Zone 1: 120-137

Zone 2: 138-152

Zone 3: 153-159

Zone 4: 160-168

Zone 5: 169-175

So what do they mean? Zone 1 and 2 are my main fat-burning zones, whereas the higher my zone, the less fat and more sugars I burn (this is true for everyone). But what was really revealing to me was that the zones I've always done cardio in have either been way too high or way too low. I was never in my fat-burning zone! That explains why I was always exhausted after my workouts-I'd been working too hard.

The good news is my fitness level is average (I suppose that's better than below average), but the trainer who ran my test pointed out that my cardio fitness could be tremendously improved if I follow some guidelines such as working out in intervals multiple times as week with two easy days, one moderate day, and one hard day.

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What I found most surprising, though, is when I go for a jog around the neighborhood I can go for much longer distances by staying in my lower fat-burning zones-now that I know what my zones are!

This insight was amazing and really changed my workouts. I'm excited to see what type of progress I make with this new information.

Do you monitor your heart rate while working out? Tell us @Shape_Magazine and @ShapeWLDiary.