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Decoding Heart Rate Zones

Posted Jan 05 2010 7:33pm

Today an old friend and I were reunited at the gym. It was a glorious moment - shouts of delight, introductions all around and a tight hug. A really really tight hug, right around my chest. No it wasn't Charlie Sheen on the rebound again. It was my trusty heart rate monitor, dug out of my sports bra drawer (what? Not everyone has an entire drawer of sports bras?), enlivened with a new battery and strapped on my person. What was the grand occasion? Lindsey's interval workout from h-e-double hockey sticks. (Side note: I had a high school teacher who insisted on spelling "sex" s-e-c-k-s every time he wrote it on the board. It was strange on so many levels, not the least of which being that to this day I still confuse "sex" with "socks.")

As part of January's Great Fitness Experiment, Personal Trainer Lindsey had us do 15 minutes of 30 second all-out-run-till-ya-puke sprints followed by one minute of recovery walking. Lather, rinse, repeat 12 times. It was a pain in the butt. Literally. Because yesterday had us do a torturous routine called a "pulse pyramid" that involved so many squats my butt cheeks remained involuntarily clenched for the rest of the day. And running wind sprints on sore buttocal - I like to make up words - muscles is excruciating.

Sore butts (and quads) aside, the Gym Buddies and I were all kitted out in our finest gadgetry for one purpose: to make sure our heart rates were in the right zone. (Okay, two purposes - we also like to compare calorie burns. With each other. With the machines. With our other heart rate monitors *cough*Krista*cough.) Because as everyone knows, when you are all-out sprinting your heart rate should be in Zone 5.

What - not everyone knows that?! Of course almost nobody knows that. Figuring out one's heart rate zones is akin to trying to locate all the noble gasses on the periodic table. While running top speed on a treadmill. And unlike the periodic table, heart rate zones are mushy science at best.

Which is why when Reader Joanne wrote me I got all excited. Well, that and she flattered me - I'm a sucker for a compliment. She writes:
"I was wondering if you'd be able to do a post about heart rate zones? I have a heart rate monitor I love - but I'm struggling with where I should be aiming for when I exercise. I get that not every session should be all out - but really I'm clueless, and while thinking about this the other day I thought of you. I love the blog and you have a skill at putting technical stuff into layman's terms."
What Are Heart Rate Zones?
Joanne, the first thing you need to understand is that fitness people are, as a rule, compulsive neurotics. And being one you know I say that with love. We love numbers. We love workouts. And therefore we love our workouts to have numbers. Basically, the heart rate zones are a set of 5 "zones" comprised of a range of heart rates, measured in beats per minute. They were designed as a way to gauge know how hard one is working (or should be working) during any given activity. Before the attack of the zones (not to be confused with the attack of The Zone, as in Barry Sears' prolific diet), people could only measure their workout intensity by their RPE, or rate of perceived exertion. This was problematic because people are notorious liars, especially when it comes to working out.

What are Your Heart Rate Zones?
This is where it gets tricky. Each zone, 1 to 5, is defined by the amount of fat being burned for fuel versus carbohydrates. You may have heard someone say, "Don't both with high intensity workouts, you're only burning carbs!" or perhaps, "If you want to burn fat, you have to stay in your fat-burning zone." So how do you know at which heart rate you reach that mythical fat-burning Shangri-La? Short answer: you don't. Not really.

Long answer: Everyone's body is different and therefore so is the rate at which they burn fat. This makes heart rate zones slightly different for each individual. In addition, people's metabolisms change over time so your heart rate zones will too. The only way to find your zones for this point in your life is to get a comprehensive metabolic test done. This involves running full tilt on an inclined treadmill with a gas mask strapped to your face until you either reach your peak heart rate or suffocate to death. It's actually a lot more fun than it sounds. Once you've done this test - and its partner the resting metabolic test - you will get a fairly accurate picture of where you burn the most amount of fat proportionally.

If you don't want to spend the money on getting regular metabolic testing done - and those tests can be very spendy - scientists have made a handy dandy chart listing the zones based on the average of people of a certain age. You've probably seen these posted on various flat surfaces at your gym. Something similar to this (chart courtesy of Polar):

click to enlarge

How to Use Them
Fit instructors, personal trainers and specific workouts will often call for a certain workout intensity. For instance, HIIT (high intensity interval training) workouts like we did today call for working at your maximum ability for short periods followed by recovery periods at a low intensity. On the other hand steady state cardio asks you to stay at a moderate intensity for a prolonged period of time. So what exactly is "moderate," "intense" and "low"? You can guess based on how you feel but most people aren't honest or self-perceptive enough to get it right. So instead of guessing, you can strap on a heart rate monitor and use the number to tell you how hard to push it.

The zones range from 1 (walking slowly) all the way up to 5 (I cannot maintain this level of exertion for more than 30 seconds without dying, puking and/or seeing stars). Depending on the goal of your workout - anything from fat loss to increased cardiovascular capacity to increased speed to rehabbing an injury - you can select the appropriate zone to aim for.

Are They Useful?
This is the real question people should be asking. I will admit to some skepticism in this area. While heart rate monitors are certainly useful for pushing yourself, beyond that I'm a little leery of their ability to make a difference that would be noticeable to anyone but professional athletes. Sure research says that doing HIIT torches way more calories both during and after than steady state cardio. But research also says that long low-intensity cardio is correlated with longevity while high intensity workouts can correlate with earlier death (chant with me: correlation is not causation, correlation is not causation...). And sure the research shows that you burn more fat in a certain zone than in others - but research has not linked the "fat burning zone" to long-term weight loss. So is it really important to know which zone you are really in?

I also think that the concept of heart rate zones makes money. The watches, the charts, the metabolic testing, the special programs, the trainers to interpret the results and design the programs - all these things cost money. Lots of money. And I have yet to see a single study that shows heart rate monitoring leading to significant athletic gains or weight loss in any but the most elite athletes. But that might just be me being cynical. I do come from good conspiracy theorist stock, I'll have you know.

Verdict
I have a heart rate monitor. I use it. You know I love numbers. For about a year I ate, slept and breathed that monitor. (Seriously - Gym Buddy Allison and I once wore ours for 24 hours just to see what our heart rates did over the course of a day.) And then I got tired of always strapping that thing on under my bra and doing jumping jacks outside the door to the child care because I couldn't end on a "weird" number of total calories burned so I stuffed it in my sports bra drawer and forgot about it. Having been on both sides of the heart rate zone loving, I will say that it can be a useful tool if you use it to motivate yourself to work harder or to calibrate your intensity to a specific workout or just keep yourself honest. However, don't expect it to produce any magical results and if you use the numbers to drive yourself nuts - or to an eating disorder - then you should ditch it.

But that's just this girl's opinion. Do you use a heart rate monitor? Love it or hate it? Do you find the heart rate zones useful?
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