Exercising at different intensities will produce different results. Depending on your goal, exercising at one intensity may help you reach your objective better than exercising at other intensities. And the best way to know if you're exercising at the appropriate intensity is to pay attention to your heart rate and understand your heart rate zones.
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For example, if you want to encourage your body to use more stored fat as fuel during exercise, you'll want to exercise at a low-to-moderate intensity. To ensure you're exercising at the right intensity, you first need to know how to calculate your target heart rate zone for fat burn.
What Does ‘Fat Burn Zone’ Mean?
If you've ever heard someone reference the 'fat burn zone,' you may be wondering what it entails.
The 'fat burn zone' refers to a time during exercise when you're working at a low-to-moderate intensity, or an intensity that's roughly 50 to 70 percent of your maximum heart rate (the number of times your heart beats per minute when it's working at its maximum capacity).
Your body relies primarily on fat and carbs as fuel during exercise, and which fuels get used largely depend on how hard you're working. When you exercise at a lower intensity, your body uses primarily fat for energy (roughly 60 percent of calories burned), as well as carbohydrates.
This is the reason why exercising at a low-to-moderate intensity is called exercising within the 'fat burning zone.' If you increase the intensity (i.e. run instead of walk or jog), your body begins using more carbs in the form of glucose (i.e. sugar) and glycogen, and you are no longer in the fat burning zone.
Read more: Normal Heart Rate When Walking
How Do You Calculate Heart Rate Zones?
To determine whether you're exercising in the fat burning zone — or any other heart rate zone — you first need to know one number: your maximum heart rate (MHR).
In general, your MHR will get lower as you age; therefore, age is a common way of estimating healthy MHR. To estimate yours, subtract your age from 220. As an example, a 45-year-old will have a MHR that's roughly 175 beats per minute (bpm).
From there, you can figure out your target heart rate zone for exercise in general, and the fat burning zone in particular.
The target heart rate zone for exercise is any intensity that gets your heart working at 50 to 85 percent of its maximum. Low-to-moderate intensity activities (ex. walking, jogging, leisure swimming) will fall between 50 to 70 percent of MHR, whereas high-intensity activities (ex. running, sprinting, playing sports) will typically fall between 70 to 85 percent of MHR.
You can easily calculate your estimated heart rate at different intensities by multiplying your MHR by the percentage you're aiming for. So, if you're 20 years old and you want to do high-intensity exercise, multiply 200 (MHR) by 0.7 to get the lower end of your target range, and 0.85 to get the upper limit.
The American Heart Association (AHA) also offers this handy heart rate chart. Here, you'll find MHRs according to age, as well as estimated target heart rate zones.
How Do I Know My Fat Burning Zone?
To calculate your individual target heart rate for exercising in the fat burning zone, take your MHR and multiply it by 0.5 to get the lower end of your range. Then, multiply your MHR by 0.7 to get your upper limit. These two numbers will give you a heart rate range to aim for during exercise.
For example, a 35-year-old will have a MHR of 185 bpm and a target fat burning zone of 93 to 130 bpm.
You can also use a target heart rate calculator to determine your ideal heart rate according to intensity. In order to use this calculator, however, you need to have an idea of your average resting heart rate.
To calculate your average resting heart rate, find your pulse with your fingers, either on your wrist or on your neck. Count the beats for 30 seconds and multiply that number by two to get your total beats per minute.
Do this every morning for at least five days, making sure to take your pulse before you get out of bed or drink caffeine. Once you have the numbers for five days, add those together and divide by five. This is your average resting heart rate.
Wear a heart rate monitor or fitness tracker during exercise so can quickly check in throughout your workout to make sure you're staying within your individual fat burning range.
One easy, tech-free way to tell if you're exercising in the fat burning zone is to try to carry on a conversation (with yourself or a friend). This is known as the 'Talk Test,' and research shows it's an accurate means for monitoring intensity during exercise. If you're trying to stay within the fat burning zone but find yourself struggling to speak in full sentences, slow down until you're able to talk without gasping for air.
A Final Word on Exercise Intensity and Weight Loss
But while low-to-moderate intensity exercise can be a great way to burn fat, you should make sure you're incorporating other types of exercise into your routine as well — especially if weight loss is the goal.
Minute-per-minute, higher intensity exercise burns more calories than lower intensity exercise. For example, a 155-pound adult can expect to burn roughly 260 calories in 30 minutes of moderate-intensity cycling, and 391 calories in 30 minutes of vigorous-intensity cycling, according to Harvard Medical School.
The advantage of exercising at a lower intensity is that it's typically easier to sustain this type of exercise. So, aim to exercise at different intensities throughout the week, and prioritize the activities (ex. running, cycling, strength training) you enjoy most.
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- Target Heart Rate Calculator
- ACE-SPONSORED RESEARCH: Validating the Talk Test as a Measure of Exercise Intensity