Your optimal fat burning zone is the heart rate (measured in beats per minute) where you maximize the rate of fat burn in terms of grams per minute.

Basically it’s the fastest way of burning fat calories.

…too good to be true?

The “optimal fat-burning zone” is a buzzword phrase being thrown around, so let’s talk about the facts that tell the whole story of burning fat calories vs burning calories and achieving your specific goals like participating in endurance events, bodybuilding, or reducing your body fat levels to improve overall health.


(Fun) Facts

Your muscles require energy as fuel. The metabolism of carbohydrates (glucose specifically) and fats supplies the muscles with energy. Oxygen is required to oxidize both fat and glucose to fuel the muscles.

Freeing energy from fat is a more metabolically efficient but slower process, while glucose provides a more readily available source of energy during periods of higher energy needs.

Humans have a finite storage of glycogen in their body that typically amounts to <3000kcal (<740g).

On the other hand, human fat storage is effectively unlimited in the context of exercise. Even very lean individuals at 10% body fat possess ~68,250kcal (7000g) of endogenous fat energy.

This has a huge impact on fat loss and health, muscle preservation, and endurance event performance.


So why IS it called an optimal fat burning zone?

The most fundamental determinant of whole-body fat oxidation rate is exercise intensity.

Different heart rate zones are based on different levels of intensity and these levels actually determine which energy systems your body uses during exercise.

The intensity level directly affects not only how MANY calories you burn, but what TYPES of calories you burn.

Fat oxidation initially increases with exercise intensity before declining at higher intensity levels.

At a low intensity level, your body is can be using anywhere from 20-80% fat as its fuel source compared to at higher intensity levels, where the primary fuel source for the muscles is glycogen. At extreme intensities, the contribution of fat to total energy approaches 0.

When you’re in the optimal fat burning zone it means your body is burning the most amount of fat per minute compared to other training zones.

By completing a VO2 max test or optimal fat burning zone test you’ll be able to define your exact heart rate zones for your body.

Not to mention also get all your personalized data inputted onto an app for your next workout!

What does this mean for weight loss, not just burning fat?

The term “optimal fat-burning zone” can be misleading, which is why we want to tell you all the facts so you know the truth.

Yes, you burn fat at the fastest rate in the optimal fat burning zone compared to other intensities, but there are 2 fine-print details to consider if you think you only need to do low intensity activities to lose weight!

1. Consider the caloric burn when working out.

If it was as simple as the percentage of fat being burned as fuel, you’d be burning a high fat percentage while at rest and you wouldn’t need to workout to have a low body fat percentage!

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You burn a higher amount of fat calories but a lower amount of total calories in the optimal fat burning zone.

Said simply; you burn a higher number of calories at a higher intensity.

So if your goal is to lose weight, then based on the simple calories in vs calories out approach to put you in a calorie deficit to lose weight, burning more calories will give you more bang for your buck to help you reach your goal faster.

This means you need to be specific in your training based on your goals.

If you have a set amount of time (ie. 30 minutes) and the goal is weight loss then you will burn more calories, and subsequently lose weight faster, from a higher intensity training.


  • 30 minutes low intensity, steady state exercise; burn 200 calories. 120 calories come from fat (60% fat)
  • 30 minutes high intensity, steady state exercise; burn 400 calories. 140 calories from fat (35% fat)

(Caveat: You can’t typically maintain a high intensity level for 30 minutes continuous so it’s not an accurate number, but in total if 15 minutes are high intensity intervals interspersed with 15 minutes of low intensity intervals it’ll still result in a greater number of calories burned, but less calories from fat.)

2. Four words: excess post-exercise oxygen consumption (EPOC)

After a high intensity workout the body continues to burn more calories which results in a temporary increase in metabolism.

The metabolic rate is 13% elevated three hours after, 4% elevated after 16 hours, and measurable effects exist up to 38-hours post-exercise.

It’s informally known as “afterburn”.

So if you do a low intensity, steady state workout you burn a set amount of calories during that time which is great, but compared to a higher intensity workout where you’ll have an elevated metabolic rate for hours afterward, the higher intensity workout is arguably better for your weight loss goals than a low intensity steady state cardio workout.


So who benefits from the optimal fat burning zone?

Endurance Athletes

If you’re training for a long distance event (triathlon, marathon, Ironman, etc) and your number one goal is performance, not burning fat, then the optimal fat burning zone is even more essential to you.

Wait, what?

Glycogen stores become depleted during exercise of sufficient length and intensity. This depletion is associated with impaired fatigue resistance and limits exercise capacity.

So an endurance athlete that has become more of a fat burner (which means they tap into more of their stored fat energy and reduce the need for re-fuelling during an event because they have an enhanced fat oxidation capacity) will have an advantage in endurance events.

Because a body has 60K calories of fat compared to only 3K calories of glucose to draw upon, enhancing fat oxidation capacity and having metabolic flexibility with substrate utilization during exercise is key training for endurance sports and, as a result, performance.

By training in the optimal fat burning zone, it primes your body to use fat as a fuel source and improves fat oxidation pathways so you don’t “hit the wall” (a sudden fatigue and loss of energy that happens to athletes during events when their glycogen stores are depleted).


Bodybuilders trying to preserve muscle mass but lose body fat while preparing for a show will benefit from the optimal fat burning zone because it helps them lean out while maintaining their muscle mass.

The optimal fat burning zone is low impact and low stress so helps bodybuilders decrease their body fat percentage without suffering from overtraining effects and losing their muscle mass.

Untrained individuals looking to improve their health and fitness + lose weight.

Training in this zone is essential for laying a foundation of using the right pathways to burn fat without overly taxing the body.

If you overdo high intensity training you risk burnout, injury, and stalled weight loss.

This lower intensity doesn’t overly stress the body and results in improved insulin sensitivity, metabolic flexibility, and lower metabolic risk factors. This is beneficial for the untrained individual looking to become more cardiovascularly fit, healthy, and still burn fat without burning out.



A higher proportion of calories burned (in grams/minute) during a low-intensity, steady state exercise at a certain heart rate level comes from fat — hence “optimal fat burning zone”.

The optimal fat burning zone is essential for;

endurance athletes looking to improve their ability to tap into fat reserves to extend the life of their glycogen stores on race day.

bodybuilders trying to preserve muscle mass and still lose fat without suffering from over training effects

untrained individuals looking to improve their cardiovascular fitness and health while losing fat without stressing the body.

The optimal fat burning zone is the fastest way to burn fat calories.

Most people don’t know their personalized zones so aren’t training intentionally. This means they aren’t reaping the maximum benefits from their training. They may never get what they want, or only make painfully and frustratingly slow progress.

People typically go either too low so they don’t maximize the benefits of the optimal fat burning zone OR too high and then aren’t purposefully burning the right fuel source.

Your training needs to be specific for your body and your goals.

The only way to find out the zones in order to elicit the desired training response, establish calorie burn numbers at various heart rates, and customize workouts to improve the efficiency and effectiveness of training to achieve your goals is from an optimal fat burning test or a VO2 max test.

If you don’t know your goals or don’t know your zones, then you’ll have a harder time getting what you want. We’re here to help you get the body and health you want.

Book your free consult here and we’ll help find what you need so you get what you want!