What energy does aerobic exercise mainly consume?

The core energy supply substrates of aerobic exercise are glycogen and fat, supplemented by a very small amount of protein. The consumption proportions of the three will dynamically fluctuate with the intensity, duration, and individual exercise base, and there is no fixed value.

Many people have heard the saying that "only glycogen is burned in the first 30 minutes of aerobic exercise, and fat is consumed after 30 minutes." Many sports bloggers have also retorted that "as long as you start to move, you will burn fat." In fact, both statements are correct, but the emphasis of the expression is different. Just like when you start driving a car, the first thing you burn when you start the car is the stock oil in the fuel tank, which is the glycogen stored in the muscles and liver. At this time, the backup oil (fat) in the trunk will also participate in a small amount of energy supply, but the proportion is very low, only about 30%, so there is an illusion of "not burning fat in the first 30 minutes."

I usually lead students to do aerobics, and usually ask them to control their heart rate at a moderate intensity that is "breathing but able to talk to the people around them normally", such as riding an elliptical machine, jogging, or brisk walking. At this intensity, the proportion of glycogen energy supply can reach 60%-70% in the first 20-30 minutes. When the exercise lasts for more than 40 minutes, part of the glycogen reserve is consumed, and the proportion of fat energy supply will slowly overtake it, reaching a maximum of about 70%. I once met a little girl who had just lost weight. She forced herself to run for an hour every day. After running for less than a week, her knees hurt. She lost body fat slowly and she still felt weak all over. Later, she was adjusted to aerobic exercise for about 35 minutes each time, and she controlled a little refined carbohydrates in conjunction with her diet. And I lost 3 pounds of pure fat in two weeks. In fact, there is no need to endure the so-called "fat energy window period" for a long time. Even if it is only 20 minutes of moderate-intensity aerobic, more than 30% of the total consumption is fat. As long as the diet is coordinated and the total calorie gap is sufficient, the fat loss effect will not be bad at all.

Fans who often run marathons must have experienced that two or three days before a race, they will deliberately eat more carbohydrates such as rice and noodles to replenish glycogen. If the glycogen is not replenished, there is a high probability that you will "hit the wall" when you run more than 30 kilometers, your legs will be too heavy to lift, and your whole body will become weak. At this time, the glycogen reserves are depleted, and the body is forced to start breaking down more muscle protein for energy. Not only will you lose muscle, but your exercise performance will also directly collapse.

People who regularly do aerobic training have a much higher utilization rate of fat than ordinary people. For the same 30-minute jog, the energy supply ratio of fat can reach 45% or higher for people who have been exercising for half a year, about 10% higher than novices. To put it bluntly, there is no need to worry about what to burn during aerobic training. Just choose the intensity and form of exercise that you can persist. If you want to focus on fat consumption, increase the duration of exercise appropriately. If you want to save time, increase the intensity a little, and you can achieve the desired effect by combining it with diet.