What does aerobic exercise mainly consume?

The main consumption substrates of aerobic exercise are glycogen and fat, which are also accompanied by the decomposition of a very small amount of protein. The specific energy supply ratio will fluctuate with the intensity, duration, and current glycogen reserve status of the body. There is no absolutely fixed ratio.

Take jogging, which is what we do most every day, for example. If you go out about 2 hours after a meal and keep the pace at a moderate intensity of 6-7 minutes, glycogen can usually account for more than 60% of the energy supply in the first 30 minutes. The glycogen here includes muscle glycogen stored in the muscles, blood sugar in the blood, and liver glycogen. They decompose quickly and supply energy without consuming too much oxygen. Just like the coin purse you carry with you, you can spend it as soon as you take it out. It is the energy that the body uses first.

Speaking of this, some people must have heard the saying that "you must do aerobics for 30 minutes to burn fat." This view was indeed the mainstream knowledge in the sports world in the early years. However, in recent years, more and more experimental data have given different conclusions: as long as you start doing low-intensity aerobics, fat has already participated in energy supply from the first minute. For example, when you take a slow walk, the energy supply ratio of fat can even reach 50% from the beginning, but the base of total consumption is too small, and the absolute value of fat burning cannot be seen. Both statements are actually not wrong, but the dimensions of observation are different. The former refers to the time point when the proportion of fat energy supply exceeds that of glycogen, and the latter refers to the starting time when fat participates in energy supply. There is no need to argue about right or wrong.

If you deliberately control your carbohydrate intake the night before and go out for a slow walk or jog on an empty stomach the next morning, as long as the pace is kept low enough to prevent the heart rate from rising too high, the energy supply ratio from fat can reach over 50% at the beginning of the run. After all, after a night's rest, most of your body's glycogen reserves have been consumed, and the body can only use more "fat deposits" to supply energy. This is why many people think that fasting aerobic fat loss is faster. However, if you suddenly increase the pace to more than 4 minutes and run out of breath and close to anaerobic state, then no matter how long you exercise, the proportion of glycogen energy supply will remain above 90%. After all, the rate of energy supply from fat decomposition cannot keep up with such a high energy demand, and you can only rely on glycogen with higher energy supply efficiency to top it off.

As for the protein consumption that everyone is worried about, which is often referred to as "losing muscle", under normal circumstances, only if you do moderate to high-intensity aerobics for more than 2 hours continuously, and when the glycogen is basically depleted, more protein will be involved in providing energy. Usually, if you do aerobics for 40 to 50 minutes at a time, the protein consumption is almost negligible. As long as you supplement your daily protein intake, there is no need to worry about it. In fact, you don’t have to worry too much about how much fat you consume each time you do aerobic exercise. As long as your total daily intake is less than your total consumption, even if you consume glycogen during this exercise, your body will mobilize fat to fill the gap in glycogen, and you will lose weight sooner or later.