Heart rate zones are a useful thing to understand if you’re trying to achieve certain goals with your workouts. With wearable fitness trackers being all the rage, it’s easier than ever to monitor how fast your heart is beating – but if the only thing you know about your heart rate is that is gets very high, very quickly as soon as you put on your gym gear, you might want to listen and learn…
If your aim for exercise is fat loss, you’ll probably be wanting to know if there’s an optimum heart rate zone for burning fat. And, well, it’s a confusing one. Because technically there is a heart rate zone where your body burns more fat, but the speed at which it burns makes it a little more complicated than that. Let us explain.
The five heart rate zones
“Heart rate zones are typically split into five training zones, which can be based off your maximal heart rate (HR max),” Thomas Roberts MSc, a health adviser at Bupa Health Clinics tells Cosmopolitan UK.
Those zones are as follows:
- Zone 1 – Very light exercise, 50-60% of HR max, able to maintain this for long periods of time, only fat burned as fuel, typically for warm ups, recovery or cool downs.
- Zone 2 – Light exercise, 60-70% HR max, sometimes called conversation pace, a mix of fats and carbohydrate used as fuel (but majority from fat), used for longer, steady activity, low energy expenditure per hour, not time efficient, good for marathon training.
- Zone 3: Moderate exercise, 70-80% HR max, carbohydrate and fat burned 50/50 as fuel sources, great for building strong aerobic base.
- Zone 4: Hard/threshold exercise, 80-90% HR max, majority of fuelling comes from carbohydrate and between 10-45% comes from fat sources, time efficient, could be a tough 30 minute session or used for longer interval sessions
- Zone 5: Maximal exercise, 90-100% HR max, high intensity interval training, should be a 9/10 in terms of self perceived exertion, fuelling all comes from carbohydrates, very time efficient, can cause muscle damage and soreness, can lead to an increased amount of muscle mass.
How to calculate your maximum heart rate
In order to work out which heart rate zone you’re working in, you’ll need to know your maximum heart rate. A simplified way of working this out, the expert explains, is to do the following calculation:
207 – 0.7 x (age) = HR maximum
So if you were 28 years old, for example, you would calculate 0.7 x 28 (which is 19.6), and take that away from 207, making 187.4 – that would be your maximal heart rate.
Now you know this, you can work out your training zones, although Thomas warns there are “limitations to this as it will vary between individuals”. If you wanted to calculate your true, personal heart rate maximal you would need to do a ‘maximal test’ under medical supervision.
So which is the ideal heart rate zone for fat loss?
The body burns fat as fuel for exercise at lower intensities (in heart rate zones 1 and 2), whereas it burns carbohydrates as fuel at higher intensities (zones 4-5). This, the expert explains, is because “fat takes longer to burn and use as energy in comparison to carbohydrates”.
“As there is a higher demand for energy at high exercise intensities, we use carbohydrates because the body produces energy from these very quickly,” he adds. “The way I like to explain it is like gears in a car; the higher the gear, the greater the fuel source needed, meaning the speed at which it is required increases, and fats alone cannot meet this higher demand for energy.”
Knowing this, it would make sense to assume that working in heart rate zones 1 and 2 (when you’re working anywhere between 50% and 70% of your maximum exertion) is best for burning fat. But that’s not necessarily the case.
“At zone 1, as a percentage you would be burning the most fat, and at zone 5 you would be burning the least amount of fat as a fuel source [because you’re burning carbohydrates instead]. However, this does not mean that zone 1 is the most effective for weight loss,” health advisor Thomas tells Cosmopolitan UK.
“You would need to work out far longer within low intensity zones 1 and 2 to burn the same amount of calories as you do at a higher intensity,” the expert explains. And ultimately, it’s the number of calories you burn which ultimately defines how much fat you lose.
“As a very simple example, not to be taken literally, if you walked for one hour in zone 2 you may burn around 400 kcal, and 90% of that may be through fat sources. But if you ran for one hour in zone 4 you may burn 800 kcal, of which around 20% from fat sources. But overall you would have burned a higher amount of calories in your run than you would in your walk,” Thomas explains.
The key rule for losing body fat
Sadly, there’s no way to ‘hack’ the system. “When trying to lose body fat, the only way to do that is through a calorie deficit,” the health advisor says. “This means eating fewer calories than you are burning. Every diet works on this same principle, but different diets work for different people and the one you can be most consistent with is the one you will succeed with.”
Diet aside, the best advice Thomas has for burning fat is to ensure your workout includes a range of heart rate zones.
“Essentially the more time you spend within a zone the more efficient you get working within that zone,” the expert tells us. “For the best outcome, work in a mix of heart rate zones to provide variety.”
Thomas Roberts MSc is a health adviser at Bupa Health Clinics, specialising in exercise physiology.
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