There is no “fat burning pulse”
It is often claimed that effective fat burning in cardio would only take place when the heart rate is around 130 beats per minute. Exercising at a higher heart rate would no longer burn body fat, but would be a conditioning exercise that tends to lose muscle mass. In addition, training in the fat burning area would have the advantage of directly breaking down body fat deposits and therefore not having to diet.
Every kind of physical stress needs energy. This is provided by both the burning calories in form of glucose from muscle glycogen stores and the burning of fats. Both types of energy production can be seen in parallel. Depending on the degree of intensity only the respective percentage share varies between the two forms. The widespread opinion that while training in the “fat burning area”, energy is derived only from fat, is a misconception. In reality, there exists no either/or. Moreover, there is only the combination of the two.
However, it needs to be said that in the “fat burning range”, the ratio of burned energy from fats to energy from glucose is higher. However, if you increase the intensity, this ratio will be less favorable in terms of fat-glucose, but it will burn even more energy, which also amounts to more fat loss. This is due to the fact that while the percentage of fat burned is less, the total energy consumption increases, which in turn also increases the absolute amount of burned body fat.
Another misconception is that the fat burning in cardio only kicks in after about 30 min. This would mean that before energy is only obtained from the muscle glycogen stores. They would have to be emptied for it first for the body to then attack its body fat storages.
This is not correct. The type of energy supply is almost entirely determined by the intensity of the physical stress, not by its duration. This means that both at low and at high exercise intensity energy is gained from both the glycogen stores and fats from the get go. Also, the latter are not only obtained from the fatty tissue like the belly, but also from the muscular fat storages.