Written by Garett Reid | NSCA, CSCS, CISSN, M.S.E.S.S
Fact checked by Kirsten Yovino, CPT Brookbush Institute
FACT CHECKED
The fitness industry loves coming up with catchy nomenclature to describe physiological systems. One of these commonly used terms is "fat burning zone," a phrase that describes low-intensity exercise targeting fat loss, which in theory, then helps you lose weight more quickly.
It's touted by many "fitness experts" as a method to burn more fat calories and improve your body composition. It's also commonly used as a marketing gimmick to promote workout programs.
So, is the fat burning zone real, and does it actually help you burn more fat than other exercises? Or, is it simply a ploy that's used to help sell workout programs?
The good news is that yes, the fat burn zone is real. But as far as whether it actually burns more fat compared to other fitness routines? That answer requires some discussion, which we're about to get into.
This post will explain everything you need to know about the fat burning zone, including:
- What is the fat burning zone theory?
- Can it help you lose weight?
- Does the fat burn zone really help burn fat and calories?
- How to best utilize the fat burning zone
What Is The Fat Burning Zone?
The fat-burning zone includes low-intensity exercise, in which your heart rate doesn't get too high, increasing the use of your fat stores for energy. The heart rate fat burn zone focuses on your heart rate, and fortunately, when it comes to how to calculate the fat burning zone, it's quite easy to figure out.
The fat burning heart rate zone occurs when your heart rate is around 50% to 72% of your maximum heart rate. This is because this exercise and workout intensity is low enough that it enables your body to rely on burning fat for fuel. This, combined with eating fewer calories than your maintenance level, helps you lose fat.
To better understand this, you need to have a basic understanding of our three metabolic systems and sources of fuel. Let's review those now.
What Are The Body's Fuel Sources?
Your body has two primary sources of fuel: carbohydrates and fat.
Carbs are often touted as the body's preferred source of fuel, but this only applies during times of high-intensity exercises, such as HIIT. This is because your body is able to break down carbs faster to quickly supply energy production in the form of adenosine triphosphate (ATP). Your body only has a finite supply of carbs, though, meaning there is a limited amount available.
However, during lower-intensity exercise or activities, such as LISS cardio, the demand for energy is not as great. Under these conditions, your body instead burns fat stores for energy. While technically there's a fixed supply of fat, as long as you are eating properly, the supply should actually be limitless.
Exercise Intensity Determines Which Metabolic System Is Used
Your body has three different metabolic systems. Through different mechanisms, these three systems are able to generate ATP to provide energy. While all of your systems are constantly working, your intensity level will dictate which energy system is favored.
The three systems include:
- ATP-CP System (Phosphagen): The ATP system is an anaerobic system, meaning it doesn't require oxygen. It utilizes creatine to synthesize ATP for very high-intensity exercise lasting less than 30 seconds.
- Glycolysis: Glycolysis is also an anaerobic system, again, meaning it doesn't require oxygen. It utilizes your glycogen stores to create ATP for intense exercise lasting 30 seconds to 2 minutes.
- Oxidative: Oxidative is the only aerobic system, which means it requires oxygen. It provides energy by using fat stores and carbohydrates to produce ATP for lower-intensity exercise lasting longer than 2 minutes.
For example, right now, you're using your fat stores for energy, assuming you're sitting down reading this, and not attempting a HIIT treadmill workout while reading at the same time (for so many reasons, please don't do this). Interestingly, the vast majority of ATP is produced by the oxidative system throughout the day.
In this context, you are in the heart rate fat burning zone even as you sleep! Then, from the moment you wake up and your activity and exercise intensity increases, you begin to gradually start using more carbs for fuel. As your intensity increases throughout the day, your body gradually shifts to using your other metabolic systems.
Does The Fat Burning Zone Work?
This all comes back to the question: What is the fat burn zone, and does it work? When we discuss the fat burning zone, this includes exercises that are performed at a heart rate for fat burn intensity, meaning low enough in intensity that your body burns calories from fat rather than carbs.
In reality, it's really just another word for steady-state cardio, like some of these recumbent bike workouts.
So, we've answered: What is the fat burning zone? Now it's time to answer part 2 of the question, which, in our opinion, is the more important part: Does it work?
Well, that depends on what you mean by "work".
Does The Fat Burning Zone Help You Lose Body Fat?
Yes. Absolutely.
However, any sort of exercise is going to ensure the body burns fat and helps with weight loss as it increases your energy expenditure. When you compare using the fat-burning zone to high-intensity interval training, studies show they both produce similar effects in terms of body composition¹.
This is important as many people also claim that fat burning HIIT is better. But, as mentioned, they're more or less the same.
The reason why something called the "fat burning heart rate zone" that uses more fat for fuel doesn't produce greater fat loss is due to its conflation with calories.
Weight loss comes when the total calories burned are more than the calories consumed. This often occurs by following a weight loss plan, such as macros counting or the 80 20 rule diet. Circling back to the fat burning zone, when you're in this zone, you may burn more stored fat, but you still have glucose stores that haven't been used.
This means that later in the day, you will use these glucose stores rather than fat. Alternatively, if you continue eating carbs and don't burn them, these excess carbohydrates that are unused will eventually turn to fat.
When it comes to high-intensity training, you will rely on your glucose stores for energy rather than your fat stores, meaning stored fat won't be burned and will add up. Your body is really smart and does a great job ensuring everything evens out.
So while the fat burning zone will utilize more fat at that moment, at the end of the day, the same results are achieved.
5 Fat Burning Zone Benefits
Wait a minute. We just said that the fat-burning zone doesn't actually help burn more calories, yet now we're talking about benefits.
Yes. Just because there's some faulty information out there, doesn't negate everything surrounding the fat burn zone.
There are still incredible benefits to using the fat-burning zone to improve body composition. Here are a few reasons why you should start including some fat-burning zone cardio in your workout split.
1. It Improves Your Fat Burning Ability.
Our metabolic systems are similar to our different muscle variables: hypertrophy, strength, and endurance. While all connected, you can adjust your load and intensity to focus on each one.
Further, if you only train one aspect, you won't improve the other variables. For example, if all you do is train muscle hypertrophy, you won't see the same amount of strength gains.
In this same way, if all you ever do is perform interval training, you miss out on improving your ability to utilize fat for fuel. Remember that the fat-burning zone happens in an aerobic condition, meaning it's distinctly different from your other two anaerobic metabolic systems.
If you always neglect this aspect in your training, you are missing out on a huge component of fitness.
2. Exercising in the fat burn zone improves workload and recovery ability.
Higher-intensity exercise is awesome. However, teaching yourself to work continuously can only be trained using moderate intensity exercise and low-intensity workouts. And by continuous, we mean longer than 5 minutes.
Remember, all three of your systems work together but independently of each other. Your body can produce significantly more ATP using the oxidative system. If you're able to increase the efficiency and effectiveness of your oxidative system, you're going to increase your body's ability to increase the total amount of ATP your body can produce during muscle recovery.
This means that when you rest, you'll be able to produce significantly more ATP, which is one of the primary reasons we take breaks when lifting weights. It enables you to recover faster and better.
Further, if you have more available ATP, you'll have more energy to perform exercises that use both lower intensity and higher intensities.
3. It improves your metabolic health & cardiovascular system.
Improving your fat-burning zone performance positively impacts your metabolic health, which is something you can't achieve by only performing high-intensity exercises.
For example, an athlete who specializes in sprinting will most likely be unable to perform well in a 5K. In other words, a sprinter will run faster but likely can't run for long periods of time without stopping.
Alternatively, a marathoner might not be able to run as fast as a sprinter, but they can likely still move quickly, and they're also able to run for a very long time.
This is because, in addition to improving your ATP production, your fitness also depends on improving your cardiovascular system. Your oxidative system is the only metabolic system that utilizes oxygen to produce ATP, meaning that it demands more from these systems.
In addition, your muscles and organs rely more heavily on receiving oxygen. During prolonged sessions in the "fat-burning zone," you place a higher demand on the utilization and distribution of oxygen.
4. The fat burn zone improves sports performance.
All sports depend on your oxidative system (aka, the fat-burning zone). Even things like weightlifting and plyo box exercises require you to be active in short bursts for a long duration.
However, once you get out of weightlifting-based sports, these systems become even more critical. Endurance running and cycling, for example, place a significant demand on these systems.
Even ball sports, such as soccer, football, baseball, and basketball, rely heavily on your oxidative system, either as a direct mechanism to produce ATP or indirectly by helping improve recovery.
5. The fat burn zone is good for weight loss.
While marketing may overdo it when it comes to this, the fat burning zone is still good for fat burn. As far as determining how long to stay in the fat-burning zone, running at 70% VO2 max for 30-45 minutes can burn anywhere from 300-500 calories (or more!).
Again, there are a lot of variables that dictate how many calories you will burn, even including things such as whether you choose to run, walk, or ride a stationary bike. And always remember that losing weight and burning fat through the fat-burning zone is just a bonus to the other health benefits you'll be getting.
How to Pick The Best Fat Burn Zone Exercise
The type of low-intensity workout you use to invoke the fat-burning zone is entirely up to you. Reaching and maintaining a fat-burning heart rate is really your only goal, so whatever helps you do that.
But for some extra guidance, keep these variables in mind when trying to burn fat.
1. Choose An Exercise You Can Perform For A Longer Duration.
In order to get the most out of using the fat burn heart rate zone, you must maintain your low intensity for an extended period of time. Going for a 10-minute jog or performing 5-minute circuit training isn't long enough to elicit the adaptations we're talking about.
While there's no set time, 30 minutes is the absolute shortest period of time to be in your targeted fat burn zone heart rate. For best results, regular trainees should target the 45-60 minute range. This is the timeframe that's often suggested to get the most out of your workouts.
2. Choose An Exercise That Allows You To Maintain Your Fat Burning Heart Rate.
Choose an exercise that lets you maintain the correct level of exercise intensity.
For example, an obvious exercise might appear to be jogging. But, can you run for 30 minutes and maintain a 70% heart rate? Swimming is another good one. Do you have the skills to swim for 30 minutes?
If you answered no to these, you should definitely work on improving those skills. But, this should be done separately from your main cardio sessions. Find an activity that aligns with your current fitness level and abilities, enabling you to stay in your fat-burning zone now (and not in 4 months when you've improved your swimming).
The Best Low-Intensity Cardio Options for Fat Burn
Keeping the variables around the fat burning zones in mind, there are three lower-intensity exercises that work awesome for just about everybody. We don't mention running, as the following options are generally easier to perform, but going for a jog works well too.
The first is cycling. Cycling is a low-impact workout, making it easy on the knees and relatively easy to maintain for a longer duration than running. In addition, it's much easier to sustain steady-state cardio as you have better control over your speed. Cycling indoors is even easier as you can watch TV or read a book to help pass the time.
Walking treadmill inclines is a great treadmill workout for weight loss. While running and jogging for 45 minutes can be difficult for some people, walking at an incline is much easier due to better biomechanics and less pounding on the joints.
Rucking is another relatively new form of low-intensity training. Well, it's not new, as it's been used for years in the military, but the fitness industry finally realized its benefits. It involves wearing a weighted backpack or pulling a light sled as you hike or walk. It's easy to perform, but you need some equipment and access to an appropriate area.
How Often Should You Perform Cardio In The Fat Burning Zone?
It all depends on your goal. If you're primarily a weightlifter or someone who wants general performance improvements, performing cardio in the fat-burning zone once per week is sufficient. This assumes you're also doing other forms of cardio with high-intensity exercise throughout the week.
If you're an athlete involved with some of the other sports mentioned in this article, you likely want to bump this to twice weekly.
And if you're an endurance athlete, you're probably already following a specialized program. Your number of fat burning zone workouts will depend on your goals, but two times a week minimum is an excellent place to start.
Train In The Fat Burning Zone To Improve Your Health
Even though the term "fat-burning zone" is overused to market fitness programs, it still has great benefits. Perhaps using concept of running zones like "Zone 2" is a more accurate way to describe the fat burning heart rate zones, but at the end of the day, both terms mean the same thing.
Improving your oxidative system by including lower-intensity exercise is just as important as following a high-intensity workout, like Tabata. Don't neglect one or the other. Include both in your training to ensure you have a well-rounded workout program.
Another Fat Burning Tool To Consider Adding To Your Weight Loss Arsenal
So, the fat burning zone isn't the magical weight-loss tool we were hoping for. The good news is that it can still help with your goals while improving your health.
And if you are searching for an additional method that can potentially help burn even more calories and shed unwanted fat, another strategy worth learning more about is fat burner supplements.
If you're interested in learning more about fat burning supplements and what they do, be sure to check out our article explaining what a fat burner is for more information.
References:
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Steele J, Plotkin D, Van Every D, Rosa A, Zambrano H, Mendelovits B, Carrasquillo-Mercado M, Grgic J, Schoenfeld BJ. Slow and Steady, or Hard and Fast? A Systematic Review and Meta-Analysis of Studies Comparing Body Composition Changes between Interval Training and Moderate Intensity Continuous Training. Sports. 2021; 9(11):155. https://doi.org/10.3390/sports9110155
Garett Reid
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