When you’re trying to lose weight, you know that cardio is the key. But what level of intensity is really most effective for burning fat?
The myth of the fat-burning zone
The theory we’re often told is that by doing lower intensity exercise, and staying within a particular heart-rate zone (60 to 70 percent of your maximum heart rate), your body will start to burn a higher percentage of fat calories. This is often called the ‘fat-burning zone’- and it certainly sounds attractive!
The idea of the ‘fat-burning zone’ is based on fact- when you’re not exerting yourself as much, your body actually does burn a higher percentage of fat calories than when you’re really pushing yourself hard. So it sounds logical that you should stay in this zone when you’re trying to lose weight.
But think about it for a second. Your body will burn a higher percentage of fat calories while you’re working out at lower intensities. But at higher intensities, you will burn a greater number of calories overall- which effectively means more fat calories burned anyway.
It sounds confusing, but look at these figures.
A 59kg woman working at low intensity (in the ‘fat burning zone’) will burn around 146 calories in 30 minutes. Of these, 50% will be fat calories. So she will be burning 73 calories of fat.
Working out at a higher intensity (80-85% of her maximum heart rare), she will burn 206 calories in half an hour. 39% of these will be fat calories. But although this is a lower percentage, it comes to 82 calories. So overall, she is burning more fat than in the ‘fat-burning zone’!
From this example, you can see that if you exercise only in this lower intensity zone, you will burn fewer fat calories during and after your workout.
Burn fat faster with intervals
This isn’t to say that lower intensity exercise isn’t good for you. Of course, it’s far better than doing nothing, and you can certainly lose weight by going slow and steady. Particularly if you are just starting out with your fitness plan, it’s important to build up your strength and endurance gradually before you start pushing yourself too hard.
But once you are at a level where you can push yourself further, if you are concerned about losing weight faster, you should add in a few sessions that really challenge you.
A good way to start doing this is to incorporate interval training into your workouts. This means alternating fast bursts of hard, fast exercise with slower recovery periods. This is a great technique because you can adapt it you your own fitness levels, giving yourself a challenge that is suitable for you.
For more information about how to use intervals to burn fat faster, check out this article on high intensity interval training.
Finding your heart rate zones
To figure out what zone you are working out in, you need to figure out what your target hear rate and maximum heart rate is. One popular way is using the Karvonen Formula:
This is an example for a person who is 23 years old, with a resting heart rate of 65 beats per minute. (To find your resting heart rate, take your pulse for one full minute while at rest. The number of beats will give you your ‘resting heart rate.’)
206.9 - (0.67 x 23 (age)) = 191
191 - 65 (resting heart rate) = 126
65% of 126 = 82 (low end of heart rate zone)
85% of 126 = 107 (high end of heart rate zone)
82 (low end of heart rate zone)+ 65 (resting heart rate) = 147
107 (high end of heart rate zone) + 65 (resting heart rate) = 172
The target heart rate zone for this person would be 147 to 172
However, there are plenty of online calculators that can work this out for you- so this might be an easier option!
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