'Fat Burning Zone' Truth: What is the Best Heart Rate to Lose Fat

The 'fat burning zone' refers to exercising at 70 – 80% of your maximum heart rate, also known as your fat burning heart rate. Achieving this heart rate zone is essential for optimising weight loss.

If you want to lose weight and keep fit, increasing the intensity of your workouts is typically recommended. But have you heard about the 'fat burning zone' theory, which suggests that exercising at a lower intensity may be more effective for fat loss?

Understanding how your heart rate relates to fat burning can help you make informed choices about your workouts.

What is the science behind the fat burning zone?

The fat burning zone theory seeks to help individuals lose weight by using the body's fat storage rather than glycogen during training. They argue that the body burns a greater percentage of fat with lower-intensity exercises than at higher intensities because the body does not require 'fast energy' from glycogen. As such, this theory promotes longer and lower-intensity cardio workouts that keep your heart rate within the 'fat burning zone', aiding in fat loss.

However, this concept may be misleading. While it is true that the body burns fat during low-intensity workouts, the total number of calories burned is lower. You would need to exercise for a longer period to burn the same amount of calories as you would at higher intensities.

In a high-intensity workout, although your body uses your glycogen stores first for 'fast energy', it depletes the glycogen stores rapidly enough to force your body to tap on the fat storage. This means that high-intensity workouts are more efficient in burning way more total calories – both glycogen and fat calories. Ultimately, the total number of calories you burn leads to the most weight (and fat) loss.

Experts explain that the concept of fat loss isn't just about ‘calories in versus calories out’, but also how efficiently your body burn fat over time.

What heart rate is ideal when exercising?

Working out with a heart rate monitor helps you to gauge the specific zones in which your body is working and how your body benefits from different intensities of exercise.

First, calculate your maximum heart rate by subtracting your age from 220. For example, if you are 40 years old, your max heart rate is 220 - 40 = 180 beats per minute (bpm).

The 4 main training zones are:

1. Warm-up zone (zone 1), 60 – 70% of max heart rate: This zone is where you prepare your cardio-respiratory system, muscles and joints to exercise harder. Here, you are functioning at a low intensity. It is a comfortable pace where you feel like you can exercise for a long time. If you are 40 years old, your warm up zone is between 108 – 126 bpm.

2. Fat burning zone, 70 – 80% of max heart rate: The fat burning zone is crucial for targeting fat loss with a moderate exercise pace. It is still a comfortable intensity but you might sweat more and breathe harder than usual. Although you may burn more fat than glycogen at this zone, the absolute amount of fat burnt is less than the aerobic stage. If you are 40 years old, your fat burning zone is between 126 – 144 bpm.

3. Aerobic zone, 81 – 93% of max heart rate: In the aerobic zone, you will be able to talk but only in short phrases. The calories you burn here split evenly between your fat stores and glycogen. Although you will not burn more fat calories than glycogen, you will be burning more calories overall. Plus, the aerobic zone makes your heart pump hard, which keeps your heart healthy. If you are 40 years old, your aerobic zone is between 144 – 168 bpm.

4. Anaerobic zone, 94 – 100% of max heart rate: Intense exercise brings you to the anaerobic zone. You are panting and unable to talk, and this is when your training is most vigourous. This high intensity can be part of a structured training regimen aimed at achieving specific goals. It is hard work and nearly impossible to spend more than a minute here as your glycogen stores are depleted faster than they can be replenished. If you are 40 years old, your anaerobic zone is between 169 – 180 bpm.

Anaerobic intervals help increase your fitness and calorie burn. This is where the 'afterburn effect', or excess post-exercise oxygen consumption (EPOC), comes into play. Your body continues to burn more calories even after your workout is over.

The intensity of your activity determines how much your heart rate increases. For example, a running heart rate should be between 50% and 85% of your maximum heart rate. You can then adjust your pace based on what you're aiming for in your run. If you notice that your heart rate is going below this, you can increase your pace to improve your workout results. If your heart rate approaches the maximum, it would be better to slow down so that you are able to finish your run.

What is the link between heart rate and fat loss?

Your body uses glucose to fuel your muscles. The two main sources are glycogen (stored carbohydrate) and fat. Oxygen is needed to break down glycogen or fat into glucose for energy.

During a workout, your body requires more energy. This increased demand for energy means your metabolism kicks into a higher gear. Thus, your heart pumps faster and harder to send oxygen to your muscle cells to break down more glycogen and fat to fuel your muscles.

While 1 gram of carbohydrate contains 4 calories of energy, 1 gram of fat contains 9 calories. This makes glycogen (carbohydrate) a less dense form of energy storage that is more readily broken down into glucose, as compared to fats. As such, glycogen is your body's first source of energy during exercise.

For effective fat burning, maintaining a balance between glycogen and fat usage is crucial. Since high-intensity workouts require more energy quickly, you tap on glycogen rather than fat for fuel. Your body only taps onto fat when you start to run out of glycogen over a longer exercise period.

How to measure your heart rate during exercise?

You can estimate the intensity of your workout by checking your heart rate. Start by finding your maximum heart rate, which is the highest rate your heart can handle during exercise. This helps you plan your training.

First, get your max heart rate (220 – your age).

Next, calculate your desired target heart rate zone. Monitoring your heart rate ensures you are operating in the best zone for your particular fitness goals. The following target heart rates are generally recommended:

• Low intensity: 50 – 70% of your maximum heart rate.
• Moderate fat burning intensity: 70 – 80% of your maximum heart rate.
• High intensity: 80 – 85% of your maximum heart rate.

Remember not to rush into vigourous exercise. If you're just beginning a exercise routine, aim for the lower end of your target heart rate zone.

Finally, to know whether or not you're in your target heart rate zone, you can use an activity tracker. If you want to measure it yourself, follow these 2 simple steps:

• Briefly stop your exercise.
• Take your pulse for 1 minute by placing two fingers on your wrist, nearer to the thumb, to get your heart bpm.

Tips for exercising - A high-intensity workout like Hyrox reaps many benefits of burning total calories efficiently both during and after exercising.

However, if you prefer a low-intensity workout such as jogging, you can exercise for a longer time to burn the same amount of calories!

To learn more about your ideal exercise routine based on your heart health, consult our cardiologists today.