Working out at a certain intensity can lead to high levels of fat burn, and you can calculate this using your heart rate.
The overview of the process goes like this: you need energy to perform, energy is stored in your body as fats and carbohydrates, low to moderate-intensity exercise is fuelled by fat, while high-intensity exercise is supported by carbs.
You’re constantly burning fat for energy, but fat can be burnt at a higher rate if the intensity of your activity increases. However, if you increase the intensity of exercise too much, your body will switch from fat to carb burn, so there’s a sweet spot if your goal is to burn maximum fat.
Of course, this is quite simplified (if you want a deeper look into this, the Krebs cycle is a good place to start), but you get the picture.
In general, your heart rate increases as the intensity of your workout gets higher, so in theory you can calculate when your body is burning the most fat based on how many beats per minute your heart is pumping at. How can you make sense of the data?
The Fat Burning Heart Rate Zone
Heart rate zones are percentages based on your maximum heart rate. The exact number for optimal fat burning heart rate will be different for every individual based on their age, gender and even fitness level.
Your maximum heart rate is simply the maximum number of times your heart can beat per minute (bmp), and there are a couple of different ways you can determine your own (more on that below).
Once you know your max heart rate you can calculate your heart rate zones, which in turn can be used to determine the intensity of a given workout.
There are five agreed-on heart rate zones you can train at:
|Zone||Intensity||Percentage of Heart Rate Max|
|Zone 1||Very light||50 – 60%|
|Zone 2||Light||60 – 70%|
|Zone 3||Moderate||70 – 80%|
|Zone 4||Hard||80 – 90%|
|Zone 5||Maximum||90 – 100%|
All zones fall between your resting heart rate (the average rate at which your heart beats when at rest, which is essentially your “minimum heart rate”) and your max heart rate.
When loss of body fat is the primary objective, exercise that optimizes metabolism of fat is a great tool.
Based on lab data, it has been established that the body metabolises the greatest amount of fat while exercising between 67.6-87.1 percent of maximal heart rate, which means your fat burning heart rate falls anywhere between those two percentiles.
Determining Your Maximum Heart Rate
The most accurate method to determine your maximum heart rate is a lab test, but you can also determine it on your own.
You can estimate your maximum heart rate with the following formula:
Max Heart Rate = 220 – your age
This is a very rough estimate and doesn’t produce the most reliable result, but it’s a starting point. Be aware that your max heart rate is affected by your physiology, which is affected by age but also influenced by many other factors.
Trying to establish a reliable result from variables you can measure statically is essentially impossible.
If you have a heart rate monitor (HRM), you can determine your maximum heart rate doing a ramp incremental test. This simply involves you exercising wearing a HRM, starting at a sustainable pace and increasing the intensity of your activity every so often (e.g. every 30 seconds) until you can’t go any faster.
The most accurate way to calculate your max heart rate is a laboratory test. These are usually conducted with a trained professional in a laboratory with high-tech equipment.
Determine Your Fat Burning Heart Rate Zone
Heart rate data can help you exercise at the right intensity for your goal.
Provided you have a reliable heart rate monitor, your heart rate is one of the most accurate measurements of intensity and effort during a workout.
When you work out in your fat-burning heart rate zone, your body will tap into your fat stores for energy. Fat calories decrease at the upper limit of the aerobic zone, when you exercise at high intensity.
Given that the optimal fat burning heart rate falls between 67.6-87.1 percent of maximal heart rate, you can determine your personal fat burning zone by multiplying your max heart rate by the minimum and maximum percentages.
This is how you can calculate your personal fat burning heart rate:
Imagine your maximum heart rate is 200 beats per minute.
67.6 percent of 200 equals 135.2, and 87.1 percent of 200 equals 174.2.
This means that your fat burning heart rate falls between 135 and 174 beats per minute, so exercising anywhere between those numbers will burn maximum fat.
Word of caution: your heart rate is incredibly responsive and can be a great tool to measure intensity. At the same time, your heart rate will change day to day depending on variables such as heat, stress, sleep, nutrition or how well-recovered you are.
Be aware that the device you’re wearing to measure your heart rate might also be slightly inaccurate.
Moreover, your heart rate sits on a sliding scale; you don’t suddenly go from fat-burn to burning carbs only, especially not if your heart rate changes by one beat. Being slightly outside of your optimal fat burning zone isn’t the end of the world.
Remember to always listen to your body and know when to take measurements with a pinch of salt.
All the advice above is based on the single goal to burn maximum fat. If your goal also includes improving your performance, a better approach to training would include sessions at different intensities to get a wide range of adaptations from exercise.