In life, we may have heard different opinions about “effective exercise time” and “basic exercise fat-burning time”. Some say 30 minutes, some say 1 hour. In fact, if you want to achieve the purpose of “burning fat”, you cannot ignore the differences in exercise intensity (exercise volume) and individual physiological differences.One thing I mentioned earlier is that 

at any time, the body’s energy supply is through multiple channels of glycogen energy supply and fat energy supply in parallel. That is to say, when exercise begins, there is fat consumption, but which one is dominant and consumes more There is a difference. A large number of scientists have confirmed this point of view through experiments. Most experimental studies have basically reached the same conclusion: 30 minutes after the start of aerobic exercise, the energy supply ratio of fat increases, which is conducive to increasing fat consumption, that is, fat loss.

Characteristics of human energy supply

To answer this question we need to know how our body’s energy is supplied.

The characteristic of the human body’s energy supply is that it will look for the optimal solution, which is trouble-free and efficient. When you first start exercising, you will first use the muscle glycogen in the muscles to provide energy (proximity principle), then use the blood sugar in the blood (transported throughout the body), and then use the liver to provide energy. of liver glycogen (broken down into glucose and released into the blood). During this period, fat is actually being consumed, but very little at first. The body’s blood sugar does most of the energy supply work.

For example: during exercise, one gram of sugar can supply approximately 4 kilocalories. Sugar releases energy quickly, so glycogen is always used first at the beginning of exercise. One gram of fat can supply approximately 9 kilocalories, and the oxidation of fat releases energy relatively slowly.

Therefore, fat needs to be used as the main energy source under certain conditions (such as after a long period of exercise).

Fat consumption requires mobilization of aerobic exercise

When we do aerobic exercise, the main sources of energy we use are sugar and fat. Sugar is mainly stored in muscles (muscle glycogen), blood (blood sugar) and liver (liver glycogen), and fat is mainly stored as subcutaneous fat and visceral fat.

As time goes by, the rapid energy supply group composed of muscle glycogen-blood sugar-liver glycogen begins to need support, and fat, the body’s huge energy treasure house, begins to show its talents.

This time is almost continuous low-to-moderate intensity aerobic exercise, such as brisk walking, jogging, swimming, etc. for more than 30 minutes*. The fundamental reason is that during this continuous exercise process, “fat mobilization” is increased. The fat in fat cells can only be oxidized to provide energy when it enters the blood and becomes fatty acids.

• Edward L. FOX, the famous pioneer of exercise physiology research, proposed in the book “Exercise Physiology” that in the first 30 minutes of aerobic exercise, sugar consumption is greater than fat, that is, the energy supply ratio of sugar is greater than fat. The energy supply ratio of sugar and fat is 50% each for 30 minutes, and they form a crossover. After that, the energy supply ratio of fat increases and the energy supply ratio of sugar decreases. This is the basis for the classic increase in the energy supply ratio of fat 30 minutes after aerobic exercise.

Later, a large number of scientists confirmed this view through experiments. Most experimental studies basically reached the same conclusion: 30 minutes after the start of aerobic exercise, the proportion of fat energy supply increases, which is conducive to increasing fat consumption.

Reference table between aerobic (lighter) and anaerobic (darker) exercise and heart rate

Fat mobilization refers to the process in which fat stored in adipocytes is gradually hydrolyzed by lipase into free fatty acids (FFA) and glycerol and released into the blood for oxidation and utilization by other tissues. During fasting, hunger or sympathetic nervous excitement, the secretion of epinephrine, norepinephrine and glucagon increases and activates lipase, which will effectively promote fat mobilization.

In fact, we often say that we need to increase fat energy supply through a certain amount of aerobic exercise, which mainly comes from the conditions of “fat mobilization”: aerobic exercise reduces sugar in the body, and exercise excites the sympathetic nerves, causing adrenaline and Increased levels of epinephrine activate lipase and promote fat mobilization.

Fat mobilization will turn fat in adipocytes into fatty acids and release them into the blood. Fatty acids can be decomposed into acetyl CoA, which is completely oxidized into CO2 and H2O and releases a large amount of energy. Most tissues can oxidize fatty acids.

If you do aerobic exercise for more than half an hour, fat oxidation provides energy as the main force. In terms of fat loss, we recommend exercising for half an hour to an hour. The first half hour is used to activate the C position of fat and allow a large amount of fatty acids to enter the blood. In the second half hour, “please start the performance of fat energy supply”.

If you only exercise for half an hour, your blood sugar will be consumed more, and fat will be consumed as soon as it is consumed on a large scale. I didn’t lose much fat, but I was hungry and my blood sugar was low. After eating a full meal like this, my blood sugar was quickly replenished.

It is worth mentioning that aerobic and anaerobic energy are not separated separately. The synthesis of these two types of energy is carried out simultaneously. It just depends on who has the greater proportion. At the muscle level, the difference between aerobic and anaerobic exercise is also reflected in the type of muscles used in the sport.

For example: Bolt has a high proportion of fast-twitch muscle fibers (anaerobic), while Kipchoge has a dominant proportion of slow-twitch muscle fibers (aerobic).

· Fast-twitch muscle fibers are characterized by fast contraction speed and high strength. They mainly provide short-term energy through anaerobic metabolism, but they do not have endurance.

· Slow-twitch muscle fibers are characterized by slow contraction speed, low strength, good utilization of oxygen, and endurance.

Exercise intensity is related to the energy source consumed

In addition to exercise time, we also need to pay attention to exercise intensity. As mentioned earlier, the human body actually supplies energy through multiple channels of sugar and fat at the same time. It’s just that sugar supplies energy very quickly. Intense exercise consumes a lot of energy and oxygen, mainly sugar. Fat supplies energy slowly but continuously. When the exercise intensity remains in the aerobic range and takes a long time, the proportion of fat supply will increase. This is why all marathon runners are so thin.

To sum up, the human body consumes energy in the following ways: if the intensity is high, sugar is mainly burned; if the intensity is low, oil (fat) is mainly burned. Maintaining low to medium intensity for a long time is the most suitable for fat loss.

One thing to note is that everyone’s physical fitness and aerobic endurance are different. “Exercise intensity” or “aerobic range” will vary from person to person. How should we judge our own exercise intensity and aerobic capacity? In what range?

For example, an expert runner may run at a pace of 5 minutes/km without sweating or blushing, while a beginner runner may be out of breath from exhaustion at a pace of 6 minutes, or even run for less than 30 minutes at all. above. Only by understanding your own exercise ability and physical fitness level can you effectively help burn fat.

Use heart rate as a benchmark to determine exercise intensity and aerobic zone

There are two elements to exercise for fat loss: a certain amount of time and a reasonable intensity.

Time is easy to control, but the difficult thing is to control reasonable exercise intensity. How do we know what is the intensity range that is suitable for us so that fat energy supply can dominate? There are various sports subjects, and individual physiological differences vary greatly. It may be difficult to be comprehensive in detail for each event and category. Fortunately, for anyone, there is one indicator that is very easy to quantify and refer to, and that is heart rate.

We can monitor different heart rate data of the body in different intensity ranges at any time.

Resting heart rate: The body’s output during low power hours,

Warm up your body and mind: Start physical activity to prepare yourself for exercise.

Fat-burning heart rate: intensity that focuses on burning fat for energy

Aerobic heart rate: improves aerobic endurance, critical heart rate improves our ability to tolerate lactic acid,

Anaerobic heart rate: In a strenuous state, it is difficult to sustain.

The fat-burning heart rate is roughly between 60% and 70% of the maximum heart rate, and the specific value varies from person to person.

For example: when my maximum heart rate is 190, my fat-burning heart rate is between 114 and 133.

When exercising (such as running) at this heart rate, the energy supply is mainly supplied by fat, and not much sugar is used. If I run faster and the energy supply cannot keep up, the proportion of energy provided by sugar will increase, and the proportion of energy provided by fat will decrease (because it is too late). It’s not that you can’t lose fat, it’s that the efficiency of fat loss is not high. Please remember that at any time, we are using multiple channels of sugar energy supply and fat energy supply in parallel, but which one is dominant is different.

In general, there are two elements to achieve efficient fat loss. One is that for more than 30 minutes, blood sugar is reduced, nerves are excited, adrenaline surges, and fat mobilization is enhanced; the other is that the intensity is controlled within the fat-burning heart rate zone (maximum heart rate 60%~70%).