What substances are consumed by aerobic exercise?

Glycogen is mobilized first, and then fat will participate in energy supply. Only in extreme cases when glycogen is completely exhausted, protein will be used.

This sounds a bit abstract, but you will understand if you recall the last time you went jogging in the park. Even if the pace is very slow in the first 10 minutes, you will be out of breath and your whole body will heat up quickly. At this time, the muscle glycogen and liver glycogen in the body are acting as the "vanguard". This thing is like the change you carry in your down jacket pocket. You can spend it when you take it out. It supplies energy quickly and does not require too much additional oxygen consumption, which is just right for a body that has not adjusted well at the beginning of exercise.

When you run for about 20 minutes, your breathing has gradually stabilized, and your sweating will not be as violent as it was at the beginning. At this time, the energy supply proportion of fat will gradually increase. When it comes to this, I have to mention the saying that "fat is not burned in the first 20 minutes of aerobic exercise" that has been debated in the fitness circle for a long time: one school of thought believes that glycogen accounts for more than 90% of the energy supply in the first 20 minutes, and the energy supply ratio of fat is extremely low, barely reaching the threshold for effective fat loss, so this is a widely circulated statement. The other group countered with the experimental data of isotope tracing, saying that even in the first minute of standing up and walking slowly, about 10% of the energy supply comes from fat, but the amount is too small to be reflected in weight changes. In fact, there is no conflict between the two statements, but the angle of standing is different.

As for the common concern about muscle loss during aerobic exercise, that is, protein consumption, it is really difficult to happen under normal training intensity. A friend of mine was in a hurry to get rid of body fat some time ago. He climbed stairs for an hour on an empty stomach every morning and forgot to replenish carbohydrates and protein after climbing. After doing this for half a month, he actually lost 2 points of body fat and 1 kilogram of muscle mass. This is because glycogen reserves are low in the fasting state. After long-term aerobic depletion of glycogen, the body can only decompose part of the muscle protein to make up for the energy gap. It is equivalent to selling the sofa and appliances at home in exchange for food, which is very uneconomical.

To put it bluntly, don’t worry too much about the order of consumption. If you do aerobics to lose fat, and you can do about 40 minutes of moderate-intensity training, the fat-burning efficiency will definitely not be bad. If you really can’t squeeze out that much time, even moving for 20 minutes is better than sitting. After all, fat is already being consumed from the first minute you start moving.