Cardio machines sometimes contain an indicator for the so-called fat burning zone. That is the level of exercise at which your body is mainly burning fat for energy. It is therefore best to train in the fat burning zone to lose weight. Or not?
During physical activity, our body can dispose of two energy stores: fats and carbohydrates (glucose). Which of the two fuels you use depends on the amount of effort. The use of fat as an energy source requires more oxygen than carbohydrates. And when exercising at a low intensity, more oxygen is available. In this way, you mainly use fats as fuel at low effort. At higher effort, your body will use relatively more glucose to get energy, so that the proportion of fats is relatively smaller.
THE FAT BURNING ZONE
People who want to lose weight are often recommended to train in the so-called fat burning zone. That’s the intensity that corresponds to about 55% to 65% of your maximum heart rate. Your maximum heart rate is 220 minus your age. At this intensity, your body gets about half of its energy from carbohydrate stores and half from fat stores. At 75% of your maximum heart rate, this ratio is approximately 65% and 35% respectively. At an even higher intensity, the proportion of carbohydrates is even lower.
To burn optimal body fat with cardio, you train at a relatively low intensity.
WHY THE ADVICE IS WRONG
It now seems like logical advice to do cardio in the fat burning zone. However, there are two reasons why the advice is wrong.
1. TOTAL CALORIES BURNED
Although you burn the most fat in percentage terms in the fat burning zone, that does not mean that you also burn the most in absolute numbers. High-intensity workouts burn more calories overall than low-intensity workouts, assuming the sessions are the same length. And so in an absolute sense you probably burn more fat.
In addition, the higher the intensity, the greater the so-called afterburn, the extra calories you burn after training. Although it must be said that afterburn is relatively small: 6-15% of the total number of calories burned during the activity.
2. TOTAL FAT LOSS OVER TIME
Fat burning is not the same as fat loss. Whether you actually lose fat and therefore lose weight, depends on the total number of calories you consume over a longer period of time.
When you burn more fat and fewer carbohydrates during a workout, you simply burn less fat and more carbohydrates later in the day and vice versa.
So, when calorie consumption is equated, a low-intensity cardio session fueled primarily by body fat is no more conducive to fat loss than a higher-intensity session fueled primarily by carbohydrates.
Remember that losing weight is ultimately a matter of calories in, calories out.
WHAT KIND OF CARDIO?
Which form of cardio is most suitable for you depends on your preference and the time you have available for it. Some like fast, high-intensity sessions like HIIT, some like moderate-intensity cycling, some like walking. You are therefore not tied to a certain shape or intensity for fat loss.
The point is that the cardio is sustainable for you and that it does not affect the recovery of your strength training.