Fitness Fact or Fiction: The Fat Burning Zone

If you’ve ever been on cardio equipment in the gym, you might have seen charts depicting different heart rate “zones” with names ranging from higher intensity “Cardio Endurance” down to a mild “Fat-Burning.” It’s not uncommon for people who want to lose fat to choose the latter intensity under the impression that it will help them reach their goal faster. This fat-burning zone is a misinterpreted idea, making it the perfect topic for a Fitness Fact or Fiction!

Energy Systems

Before we can talk specifically about the fat-burning zone, let’s get an idea of what the body does as our heart rate increases!

Anytime we engage in physical activity, our body uses energy to fuel us. This energy is provided by the carbs, proteins, and fats we eat. However, there are different forms of energy transfer depending on what activity we engage in.

These energy systems are the ATP-PC, glycolitic, and aerobic systems. The aerobic system is what comes into play for this fat-burning zone myth.

ATP-PC

ATP-PC stands for adenosine triphosphate-phosphocreatine (try saying that fast three times!). Energy is released from the breakdown of phosphocreatine, a chemical compound stored in the muscles.

ATP stores only last a few seconds, followed by the breakdown of PC for another 5-15 seconds. In total, this energy system can sustain 10-15 seconds worth of high-intensity exercise. After this, other energy systems are used.

Glycolytic (Anaerobic)

Glycolysis is the breakdown of glucose, which summarizes how this system works! To provide energy through glycolysis, glucose or glycogen (the stored form of glucose) is broken down to form ATP (the same compound mentioned above). Anaerobic means without oxygen as this system doesn’t rely on oxygen for fuel (though ATP-PC doesn’t rely on oxygen either). This system provides 10 seconds to 2 minutes of energy, used during short, intense exercise. 

Aerobic

This is where the misconception of the fat-burning zone comes in. The aerobic system is utilized more than the other energy systems and provides energy for low-intensity activities. It can last from 2 minutes to a few hours. In addition, unlike ATP-PC and glycolysis, the aerobic pathway requires oxygen. In addition, this system takes much longer to overload.

In the aerobic energy system, fuel comes from carbohydrates and fats. The more intense the exercise, the more fuel comes from carbs. The more effort you put in, the more carbs your body is using to fuel you. This specifically leads to the misconception of the fat-burning zone!

The Fat Burning Zone

It’s true that less strenuous activities rely on carbs and fats through the aerobic energy system, and that higher intensity relies more on carbohydrates. With these seemingly supportive facts, the belief is that exercising at a lower intensity will burn more calories from fat, leading to faster/more efficient fat loss.

The fat-burning zone is determined by one’s heart rate, roughly 50-60% of a person’s maximum heart rate. The standard equation to determine maximum heart rate is 220 minus your age. For example, mine is 220 – 25, or 195 beats per minute (bpm). Again, this is a general estimate but might not be true for you individually. 

So (again, in very general terms,) the “fat burning zone” could be from 88 bpm up to 110 bpm depending on age. This range could be a brisk walk, or even slightly less intense than that.

Exercise at a lower intensity and burn more fat– this seems like a good deal, but it’s actually a flawed idea.

It’s True…But Also Not

While more fat than carbs (aka glycogen) are burned in this specific heart rate range, the idea that this range is best for fat loss is fitness fiction.

It’s true that a higher percentage of fat is burned in this lower-intensity range. However, at a higher intensity, more total calories, and therefore more calories from fat are burned overall. While fat loss really isn’t as simple as energy in vs. energy out, more intense cardio will increase the energy output, potentially causing a reduction in weight.

Cardio is, understandably, not everyone’s favorite activity, but it’s so important for a number of bodily functions and disease prevention. Cleveland Clinic highlights some of the benefits of cardio exercise, ranging from fighting osteoporosis to decreasing the risk of type 2 diabetes.

What’s Best?

Cardio is great, but if fat loss is one of your goals, then resistance training is essential. Aerobic exercise can strengthen our cardiorespiratory system but does little to help build muscle. Engaging in regular resistance training and developing muscles is a helpful and sustainable way to lose weight. Muscles require a fair amount of energy, meaning increasing your muscle mass can also increase your metabolism. In other words, your body will require more energy (food) to function properly

I recommend a combination of both cardio and strength training for a well-rounded exercise routine, regardless of goals. If this is something you want to talk about and how we can make this recommendation work for you, sign up for a consultation or contact me!

The Takeaway

While there’s nothing wrong with a few lower-intensity cardio workouts, don’t be afraid to get your heart rate up! The idea that staying in a lower heart rate zone is best for fat loss isn’t true, and bumping up the heat will help you burn more calories overall if that’s related to your goals.

For sustainable fat loss, don’t rely on a bunch of cardio and nothing else. Add some weights into the mix to build more muscle and not only be stronger but increase the amount of energy your body needs to function.

Myths like this are tricky because, at a surface level, they make sense. This is how they’re spread both by individuals and by health and wellness professionals who feel they’re offering the answers their clients want to hear.

I would love to tell all of my clients that their goals can be met and problems solved with quick fixes, miracle pills, and some brisk walking. However, I think it’s more important to be realistic about the work that needs to be done to have a body that works as well as it can and keeps us going. Even so, we can also acknowledge and accept that it’s hard work and sometimes sucks!