You have committed yourself to a daily gym pilgrimage, proclaimed yourself a born-again gym rat and are on a mission to lose that 15-20 lbs around your middle. You step up to a vacant elliptical, locate the obligatory cardio zone sticker on the console, find your age along the horizontal and follow the invisible line vertically until it intersects into the promised land of a slim, svelte, hard body future.
You grab the metal part of the handles to make sure it picks up your heart rate like a thousand other sweaty paws have done before you as you begin to grind and toil away all of your culinary indiscretions, and you focus on diligently keeping your heart rate in the “fat burning” zone to try and make sure it is time well spent.
Sound familiar? Ask yourself, how long did you go before you questioned whether you were working out hard enough to be doing any good. Have you wondered or even asked the question, “Is this really my fat burning zone? What IS the true best heart rate to burn fat?”
You see those cute little charts or graphs emblazoned on treadmills and ellipticals in gyms all the time depicting multiple training zones. There is usually one particular cardio workout zone that attracts the most attention, the holy grail of all cardio zones, the “fat burning” zone. But does it really live up to its billing? Let’s draw back the curtain on this and see, shall we?
The Problem With Traditional Heart Rate Formulas
Let’s start by looking at traditional thought and the source of all those colorful charts and graphs you see hanging in gyms and on the consoles of most cardio machines. We are talking about the tried and true classic formula for figuring out target heart rate zones… well “tried” anyway.
You will find that there is more than one formula to calculate target heart rate zones from, but they all have one thing in common, they are all based on and include your max heart rate (MHR) in the mathematical equation.
220 – Age = Max Heart Rate
This is the same formula burned into my gray matter from way back in an exercise physiology class in college, as well as drilled into every personal trainer in the land. But where the heck did the constant 220 come from? How accurate is this formula?
I say tradition, because this formula has been with us since the 1930s. It should also be noted that the formula hinges on an estimation of max heart rate. I will be honest with you, I have yet to see this formula in a textbook with any sort of explanation or cited source for research talking about where the heck 220 comes from.
“Ironically, inquiry into the history of this formula reveals that it was not developed from original research, but resulted from observation based on data from approximately 11 references consisting of published research or unpublished scientific compilations. Consequently, the formula HRmax=220-age has no scientific merit for use in exercise physiology and related fields. A brief review of alternate HRmax prediction formula reveals that the majority of age-based univariate prediction equations also have large prediction errors (>10 b/min). Clearly, more research of HRmax needs to be done using a multivariate model, and equations may need to be developed that are population (fitness, health status, age, exercise mode) specific.”Robert A. Robergs & Roberto Landwehr, Journal of Exercise Physiology
From the research I have read, the constant 220 is based on the average when outliers were removed and a linear graph was plotted. At any rate, this is the standard formula you will find in textbooks, study materials, and exams within the fitness industry, even though research done in the last 20 years has shown a large margin of error when estimating max heart rate (MHR) anywhere from +/- 10 to 20 bpm from the studies I have read.
It should be noted that age is taken into account because your MHR will decline with age. Hirofumi Tanaka, associate professor of kinesiology and health education at the University of Texas and director of the university’s Cardiovascular Aging Research Laboratory states, “Maximum heart rate is unrelated to exercise training. Whether you’re a couch potato or a highly trained athlete, that rate declines about seven beats per minute for each decade. Regular exercise can lower your resting heart rate, but it does nothing to slow the age-related decline in maximum heart rate.”
Target Heart Rate Zones
If you try a Google search of your own, you are going to find many different opinions on target heart rate zones. You will see articles and charts with anywhere from 3-7 heart rate zones with a varying collection of flowery terms for each zone. I apologize on behalf of the fitness industry for failing to come together and agree on what to call these zones and come to a consensus on how many zones we need. Falling back on my endurance sports background, I will admit I am most comfortable with 5 target heart rate zones.
Zone 1 – Active Recovery Zone (50%-60% of MHR)
You might also see this called a “Warm-Up Zone.” This is a great intensity level for warming up, cooling down or recovering from a hard workout session. You may also see this labeled by some sources as “Fat Burning” zone.
Zone 2 – Endurance Zone (60%-70% of MHR)
As an endurance athlete, this is what I would refer to as “social pace,” meaning this is an intensity level that I can literally hold and ride or run for hours. Conversation can be had at this intensity level. Think of it as a cruising speed. You might also see this called “Aerobic Development Zone.” You might see this zone referred to as a “Fat Burning” zone as well. This is largely considered the zone used to build base fitness, due to the theory that this workload level teaches your body to burn fat as fuel and to produce more mitochondria.
Zone 3 – Aerobic Endurance Zone (70%-80% of MHR)
Tempo and “Aerobic Endurance” are commonly interchanged terms used to describe Zone 3. I will admit, Zone 3 is my personal “happy place.” When riding or running tempo you are working on your ability to comfortably maintain a hard pace. It’s like riding or running hard, but not too hard. Think of it as dipping your big toe into “The Hurt Locker.” You are just kind of testing the waters a little bit before committing fully to going all in.
Zone 3 is ideal for increasing aerobic capacity as well as some of the same benefits we talked about above in Zone 2. The main difference being that training in Zone 3 is much more tiring than Zone 2, so the time duration per workout session will tend to be a bit shorter for Zone 3 training vs. Zone 2.
Zone 4 – Anaerobic Endurance Zone (80%-90% of MHR)
Once you hit Zone 4 you have crossed the line and entered the “hurt locker” or properly known as anaerobic threshold. I should be more specific: Zone 4 starts just below the anaerobic threshold and finishes just above it. Zone 4 is where you start to see a variety of interval training take place, as well as a high production of lactic acid.
Lactic acid (LA) is one of the byproducts of metabolism. As your workout intensity and energy demand goes up, your metabolism speeds up to meet the demand. Your body will eventually get to the point where it can’t keep up with flushing or ridding the muscles of the buildup of LA from your effort. This is what causes that burning sensation in your muscles while you are working out. This is where the term “threshold training” comes from. Welcome to the “pain cave” my friend!
Zone 5 – Anaerobic Capacity Zone (90%-100% of MHR)
This is, “Crush your enemies, see them driven before you, and hear the lamentations of their women” effort. There is nothing here for you in Zone 5 but pain and misery if done correctly. Obviously, this is going to be work done in short, all out, unsustainable bursts. It is extremely fatiguing work with the sole purpose of working on cardiac output. Basically, it’s about how much and how quickly the heart can pump blood to those working muscles.
The Most Common Formulas Used For Determining Target Heart Rate
Let’s take a look at and compare a few accepted or commonly used formulas for figuring target heart rate zones, just to illustrate how much they can vary. Let’s use the same numbers for the sake of consistency.
Say a male subject is 40 years of age and has a resting heart rate (RHR) of 60 beats per minute (bpm). I will also use the percentages established by a study at BYU’s human performance lab to determine the best “fat burning” zone, i.e., 68%-79% of max heart rate (MHR).
First things first, we need to figure the MHR for this male subject:
220 – 40 = 180 BPM
Now, let’s calculate this male subject’s target heart rate for fat burning using some of the common formulas:
(MHR) %intensity level = Target HR Zone
(180) 68% -79% = Target HR Zone
(180).68 to .79 = 122.4 to 142.2bpm
((MHR − RHR) × %Intensity) + RHR =Target HR Zone
((180-60) x 68% – 79%) + 60 = Target HR Zone
(120 x .68 to .79) + 60 = Target HR Zone
(81.6 to 94.8) + 60 = 141.6 to 154.8bpm
Uses 208 – (0.7 x age in years) for MHR
208 – (.7 x 40) = MHR
208 – 28 = 180bpm MHR
180 x .68 to .79 = 122.4 to 142.2bpm
I am guessing about now you are wondering which of the three is the most accurate computation to use. Even though the “Traditional” formula and the Tanaka formula came up with identical parameters for “ideal” fat zone, I would submit to you that the Karvonen Formula would be truer to form of the three. The reason is, it is the only one of the above to take your resting heart rate into account. The reason this is important is that resting heart rate is a good indicator of how fit the heart is.
Think about resting heart rate this way. The average heart pumps about 5 quarts of blood in one minute. Now if your heart can pump 5 quarts of blood in one minute with 10-20 fewer beats per minute than the average Joe, you can see how your heart is working much more efficiently.
Now with that being said, realize that all three formulas are max-heart-rate based which we have already established is a complete guesstimation and fall far short of being accurate. Need more proof?
Exercise physiologist Dr. Fritz Hagerman, who has studied world class rowers for three decades, has said that the idea of a formula to predict an individual’s maximum heart rate is ludicrous: he has seen Olympic rowers in their 20’s with maximum heart rates of 220, and others on the same team and with the same ability, with maximum rates of just 160.
So If Formulas Aren’t Absolute, How Do I Calculate My Personal MHR?
Another issue with all the research and the old school traditional 220 − age thing is that this is targeted at groups of people, not individuals. Think of it as a VERY loose guideline. The way to dial this in for you personally is to use yourself as your own personal lab rat.
A sure fire way to figure it out is to go out on the road and see what you have got under the hood. A heart rate monitor is a VERY helpful tool for this process. I will use cycling as the example here, being that it is my sport of choice and I tend to work with a lot of cyclists, however, this can be modified on the run as well.
After warming up, ride for 10 min at a steady pace. Follow this with 10 min of riding progressively harder turning up the wick every two minutes over the 10 min duration. Then spin the legs out nice and easy for 10 min before starting the testing period. Pick a route or section of pavement where you can ride continuously without stopping for 5 min. If you can find a slight incline, this would be ideal.
Start the clock and spool up to a speed you think you can carry over the entire 5 min test. Every minute, raise the pace a bit and continue until you feel you are right at your limit and then sprint as hard and as long as you can. Check your heart rate and call that your max.
OK, So I’ve Figured Out My MHR, Now What’s The Best Heart Rate To Burn Fat?
OK, now we are getting to where the rubber meets the road! This is a bit of a myth and is easy to see where some confusion comes into play. To understand where this myth comes from and figure out how to lose weight the most efficient way possible, we need to comprehend some basic physiology.
The human body can run on three different types of fuel: fat, carbohydrate, and protein. I mention protein and yes, we can run on it but it is the last thing the body will burn for fuel. Think of it as something the body will use if it is in starvation mode. Your body would much rather use protein as a building block than an energy source. So that leaves us with fats and carbohydrates for our primary sources of fuel. Let me take a step back and swap out the term carbohydrates for glycogen. Glycogen is basically how your body stores carbohydrates in your muscles and liver.
You are always burning both glycogen and fat for energy. The ratio of fats to glycogen being burned is what varies depending on exercise intensity and duration. This is where the confusion comes from and how a myth is born!
It has been shown that in the lower cardiovascular intensities found in Zones 1 and 2, a higher ratio of fat to glycogen is burned. So, it’s easy to see how the myth can take hold, if my body burns a ratio of 60% fat to 40% glycogen at 50% of my MHR. My lazy side is all over that like a hobo on a ham sammich!
However, it has also been shown that at 75% of your MHR the ratio swings the other way: 35% fat to 65% glycogen. As the intensity level rises, the ratio continues to slide even more to the glycogen side. Right about now you are wondering to yourself, “Why would I want to do any cardio above Zone 1 or 2 then? Why work so hard?”
You need to shift your thought process to net or total calories burned, and not get locked in on burning calories from fat. Yes, you will burn a higher percentage of fat at a lower intensity, but the higher the intensity level the more NET calories you will burn, which is the most important result. Maybe a visual aid would help get the idea across better:
|60-70% MHR||80-100% MHR|
|Total Calories Burned||200||300|
|Calories Burned From Fat||120||135|
|% of Calories Burned From Fat||60%||45%|
|Best Heart Rate To Burn Fat?||No||Yes|
Your big takeaway here is that regardless of where the calories come from, total calories burned is what you should be looking at. Although the fat calorie percentage was higher at 60-70% MHR, you still burned more fat calories in total at 80-100% MHR.
Benefits of HIIT and EPOC For Fat Burning
Recent studies have shown that people who participate in shorter, high-intensity interval training (HIIT) workouts vs. the normal garden variety cardio user who follows the target HR sticker on a cardio machine are three times more successful at burning fat. It should be noted that HIIT is the training philosophy that circuit training/Crossfit was born from.
The other drawback to working out in that traditional low-intensity state is you miss out on the EPOC effect or “afterburn.” As your workout intensity goes up your muscles will require more oxygen, and at some point your heart will not be able to keep up with the demand.
To correct this deficit your body will be in an elevated metabolic state even after the workout is over, in an attempt to supply your muscles with what it needs to re-achieve happy homeostatic bliss. This elevated post workout metabolic state is called Excess Post-exercise Oxygen Consumption or EPOC response.
Now, before you get all giddy like a schoolgirl over EPOC, keep in mind that the bulk of your calorie burn is during your Zone 4+ workout session. It is true that the higher the intensity level during your workout the better the calorie burn in the resting post workout state, however, recent studies are showing that it may not be as much calorie burn as some of the hype may indicate.
“Tanaka, Shibuya, and Ogaki examined the EPOC of 7 x 30-s intervals with 15-s rest periods at 150% of VO2 max. They found that the three-hour EPOC value was 10.5±2.4 L of oxygen, which amounts to approximately 50 kcal over the period of three hours or 16 kcal per hour. Bahr, Gronnerod, and Sejersted examined the effects of sprint volume on EPOC, having subjects perform 1, 2, or 3 x 120-s sprints at 108% of VO2 max. They found that higher volumes of sprint training elicit a higher EPOC, but that even at the 3 x 120-s sprint, the four-hour EPOC total was 16.3±3.01 L of oxygen, or about 80 kcal of extra energy expenditure.”National Strength and Conditioning Association
So, basically over a four-hour period you raised your metabolism rate due to EPOC enough to burn the equivalent of a large egg. Don’t get me wrong. It’s something, but might not be worth the hype that some claim.
Best Way To Monitor Heart Rate
With all of this talk of max heart rate and resting heart rate and zone this and zone that, blah, blah, blah… you might be wondering what is the best way to get instant feedback. With wearable tech becoming more and more popular and new options popping up overnight like zits on a hormonal teenager, what is your best option? What is most accurate?
You can divide your options into two types of monitors. The first, and what seems to be trending the hottest right now (thanks to Fitbit and company), is an optical heart rate monitor worn on the wrist.
This type of monitor uses light to track your pulse. Blood will absorb light and the fluctuations in light levels vary with your pulse which can be detected by your wearable device and converted into a heart rate.
The second type is the more traditional chest strap monitor, which detects and measures the electrical activity of your heart like an EKG will do. The chest strap will act as a transmitter and send the info to some sort of receiver, whether it be a handlebar-mounted device or a wearable device on your wrist.
Which Is Better, Wrist Monitor or Chest Strap Monitor?
As far as accuracy goes, the chest strap tends to be more accurate. Think about it this way: it is closer to your heart and is reading electrical activity, where the wrist monitor is at the end of your arm and is reading blood flow that will be a slower feedback loop than the electrical activity picked up by a chest strap.
Tests have proven that most chest straps have shown a similar accuracy to a hospital grade EKG, where the wrist monitor has proven to not be as accurate due to the reading being affected by light leaking in and influencing the sensor. For this reason the wristband needs to be worn on the snug side. Below are some of the most popular chest strap heart rate monitors being sold on Amazon:
Now, before you run out and buy a chest strap type heart rate monitor, realize they lose a lot of customers due to comfort issues. I have worked with my fair share of marathon runners, and I can’t say too many of them are fans of the chest strap. They can get a bit uncomfortable and rub you raw after about an hour or so of use, maybe even less for those of you of the well-endowed female persuasion, shall we say.
From my own experience I can tell you they are certainly more comfortable on the bike vs. the run. However, with that being said, they can feel a bit too constricting on both for some.
Final Thoughts About The Best Heart Rate To Burn Fat & The “Fat Burning Zone”
I will be honest, Zone 1 and Zone 2 still have their place. It’s just that, in my opinion, they are mislabeled. They are great for recovery workouts and warming up or cooling down, but for the best use of your time, Zone 4 is where you should be for dropping pounds and getting lean.
I would scrap the traditional MHR constant of 220 in your calculations, and it might be a good idea to consult your physician before lacing up your running shoes or jumping on a bike to test and see what your actual MHR is. Once you figure out your MHR, you are ready to do the math.
Keep in mind that if you are not used to working out, jumping into the deep end and trying to work out for any length of time in Zone 4 probably won’t happen. You will need to work yourself up to the point you can handle that workload. Either way, weight loss can be a tough journey, but as long as you stay consistent and determined, the fat will be gone before you know it!
ABOUT THE AUTHOR
Tim is a full time gym manager/personal trainer, part time gym designer, part time blogger and part time pseudo-entertaining public speaker as well as a former college athlete and former firefighter with a BS degree from Fresno State in Kinesiology and an AS degree in Respiratory Therapy. His passion is seeing everyday people get healthy and live life to the fullest.