Aerobic exercise energy supply sequence

From 0 to 10 seconds after exercise starts, the phosphagen system is the main source of energy. From 10 seconds to 3 minutes, the glycolysis system accounts for the highest proportion. After 3 minutes, the aerobic oxidation system becomes the core.； The proportion of energy supply in the aerobic-dominated phase will continue to adjust over time. In the first 20-30 minutes, glycogen (muscle glycogen, blood sugar) is the main energy supply. After that, the energy supply proportion of fat exceeds glycogen and becomes the largest energy source. The proportion of protein throughout the entire energy supply does not exceed 10%. It will only increase to 15%-20% during long-term exercise when glycogen is completely depleted.

Many people have heard the saying "you must run for more than 30 minutes to burn fat" when they first came into contact with sports. To be honest, this statement is not completely wrong, but it is definitely not the truth. If you think about it based on your own exercise experience, you may have touched the edge of this rule long ago.

For example, the last time you went for a night run on a whim, you ran faster than anyone else in the first few dozen seconds after you left the house, and you were still able to say hello to the man walking the dog on the roadside. After running for a minute, you started to pant, and you couldn’t even speak, and your thighs started to get sore. That means that your phosphate supply has been exhausted, and glycolysis has taken over. Lactic acid accumulates quickly at this stage, and many people just can't hold it for two or three minutes and give up directly. If you grit your teeth and get through it, and after about 5 minutes, your breathing becomes more even, your cadence becomes steady, and you can even hum a non-stop song in your head, that means your aerobic system is officially online.

In fact, these three energy supply systems are like the three emergency foods you prepare at home: Phosphate is an energy gel that you carry in your pocket. You can eat it when you tear it open. When you are very hungry, you only have one bite and it will not last long.； Glycolysis is the quick-frozen dumplings in the refrigerator. It can be cooked in 10 minutes. The quantity is larger than energy gel, but eating too much can lead to acid reflux (corresponding to the accumulation of lactic acid). ； Aerobic oxidation is your slow-cooked tomato beef brisket on the weekend. It takes half an hour to cook to get the flavor. It has enough calories and is filling and comfortable to eat. It corresponds to the characteristics of fat supplying energy for a long time and less metabolic waste.

Nowadays, the fitness circle is quarreling over "whether it is necessary to stay up for 30 minutes." One group is based on the old view of traditional exercise physiology, which says that only after 30 minutes, the energy supply of fat accounts for more than 50%, and if you want to lose fat, you have to spend enough time.； The other side is the conclusion of clinical research in recent years, which says that even if you just go downstairs and walk briskly for 10 minutes, fat accounts for about 30% of the energy supply. When I teach students, I usually mention both. If you have enough time and energy, a 40-minute run is of course more cost-effective. If you are too busy with 996, taking 10 minutes to climb the stairs every day is better than lying on the sofa and scrolling through your mobile phone. There is no need to be stuck in a dead line for 30 minutes. On the contrary, it will put a psychological burden on you, and you will feel that you have no time to move.

Oh, by the way, some people say that fasting exercise burns fat faster. This is indeed true. When you are fasting, glycogen reserves are low, and the energy supply from fat may exceed 50% in about 15 minutes. However, I really don’t recommend that novices try it blindly. Last month, I met a little girl who squatted on the side of the road for 8 minutes on an empty stomach and turned pale and vomited. It hurt the body. If you have no exercise foundation, it is safer to eat a small bread as a cushion before moving.

There was a student who was preparing for a half-marathon. At the beginning, he always liked to rush the pace for the first 5 kilometers. At 15 kilometers, he would hit the wall and his legs would feel as heavy as lead. Later, he adjusted his strategy. The pace for the first 5 kilometers was 10 seconds slower than the target pace. He tried to keep his heart rate in the aerobic zone, so as not to use up all the glycogen at the beginning and save it for the second half of the race. He later ran the entire distance without hitting the wall, which is because he understood the rules of energy supply.

There are also many people who are afraid of losing muscle while running. In fact, there is no need to worry. For normal aerobic training, such as running for 40 minutes, protein energy supply accounts for only about 5%. Unless you run for more than 2 and a half hours in a row and all glycogen is depleted, the body will decompose a large amount of muscle for energy. Ordinary people who lose fat cannot reach this threshold. If you add an egg or a glass of milk after running, the lost protein will have been replenished.

In fact, there is no need to memorize these energy supply time points. In the final analysis, exercise is about getting along with your body. You can feel when you are tired and when you feel comfortable. Just follow your body feeling. After all, exercise that you can persist in is the exercise that is effective for you.