Is the damage sustained in the whole body and the abdominal area the reason for fatigue due to exercise? What you should know in order to achieve optimum performance!

Many individuals want to get better or become stronger. Hence, they train for a long time, undergo more intense training, or work too hard. However, simply lengthening or intensifying training does not necessarily allow better performance.
When exercising intensely for a long time, damage to the whole body, muscles, and also the abdomen can occur. In this section, we'll look at the damage to the abdomen and think about the problems that originate in the body at this time.

1. Depending on the duration and intensity of the exercise, the abdomen may become damaged. What effect does damage to the abdomen have on the damage to the entire body and performance?

As shown in Figure 1, when a person trains over a long period or performs high-intensity exercises, the body can be damaged. Many people know that damage to the muscles can cause inflammation including muscle tightness and muscle pain. Inflammation is a normal response that originates to protect the body from stresses, such as intense exercises. However, if the inflammation is too severe, pain and swelling may occur. In fact, this inflammation occurs not only in the muscles but also in the whole body. If inflammation is present in the entire body, fatigue is more likely to occur, and the expected performance is less likely to be achieved 1), 2).

It may be difficult to notice, but prolonged or intense exercise may also cause damage to the abdomen 3).

Damage to the abdomen alone is a major problem for sportspersons. However, such problems can lead to even worse inflammation throughout the body. This leads to an inability to perform as expected.

Figure 1

1) Cerqueira E, et al. Front Physiol. 2020;10:1550
2) Robson-Ansley P, et al.Int J Sports Physiol Perform. 2009;4(2):186-94
3) De Oliveira EP, Burini RC.Curr Opin Clin Nutr Metab Care. 2009;12(5):533-8

2. If you continue to exercise, the body temperature will increase and blood flow to the abdomen will decrease!

We have introduced the fact that prolonged exercise and increased intensity can cause damage to the abdomen. So why does this kind of damage occur? Here, we will explain the potential causes. The body temperature in the body increases too much and the blood flow to the abdomen decreases.

Exercise increases the internal temperature of the body. When this happens, sweating and evaporation from the surface of the body tend to reduce the temperature. However, when exercise is prolonged or is intense, sweating alone cannot reverse the rising body temperature, resulting in a higher body temperature.

There is a relationship between the change in body temperature during exercise and the damage caused to the abdomen (Fig. 2). When the body temperature rises to about 38.6 to 39.0℃, about 60% of the individuals sustain abdominal damage, and when the temperature rises to 39.0℃ or higher, some data suggests that 100% of all individuals are affected 4).

Figure 2

Next, we will look at the deterioration of blood flow to the abdomen when you exercise. Exercise increases the heart rate and the amount of blood pumped from the heart to the whole body. Why, then, does the flow of blood to the abdomen is low? Typically, this is observed because blood is delivered preferentially to the muscles during exercise, and the amount of blood delivered to the abdomen is low.

Figure 3

Figure 3 shows that when you exercise, less blood is observed in the abdomen (internal organs). When the subjects cycled for approximately 60 minutes at a 'slightly intense' level, the flow of the blood to the abdomen was lowered by as much as 80% compared to that in the subjects who did not exercise 5). This reduced amount of blood to the abdomen means that the abdomen (internal organs) cannot receive the required oxygen. If this occurs, the abdomen (especially the small and large intestines) may be depleted of acid, causing adverse effects.

In other words, depending on the duration and intensity of the exercise, the body temperature can increase or the blood volume can decrease, resulting in damage to the abdomen.

4) Pires W,et al. Sports Med.2017;47(7):1389–403
5) Ter Steege RW, Kolkman JJ. Aliment Pharmacol Ther.2012;35(5):516–28

3. Damage to the abdomen due to exercise may worsen damage to the whole body

Depending on the duration and intensity of exercise, damage can be sustained in the abdomen (especially to the small and large intestines). Next, we will look at the mechanism by which such damage can affect the whole body.

Approximately 1000 types of intestinal bacteria are present in our intestines, totaling about 100 trillion. Half of these intestinal bacteria produce toxins.

Figure 4

As shown in Figure 4, in a healthy intestine, many cells are arranged evenly without gaps on the surface of the intestine. These conditions provide adequate abdominal protection, and gut bacteria and toxins that are produced cannot pass through as they are blocked by evenly arranged cells 6).

However, when exercise damages the abdomen, cells in the intestine are damaged, resulting in gaps between cells. If this occurs, the ability of the body to protect the stomach is diminished, and the bacteria and toxins in the gut slip through the gaps and enter the bloodstream, thereby worsening the overall inflammation of the body. If the inflammation worsens, fatigue is experienced more easily. It is not possible to maintain good health or achieve the targeted performance.

6) Clerk A, Mach N. J Int Soc Sports Nutr.2016;13:43.

4. High temperature and high humidity may exacerbate the abdominal damage caused by physical exercise!

We have explained that prolonged exercise or intense exercise may increase body temperature or reduce the blood flow to the abdomen, resulting in abdominal damage. Such problems may worsen when people are exposed to high temperatures and high humidity like the summer in Japan 7).

Figure 5 shows the changes in body temperature during a 60-minute run of slight intensity at normal (22°C) and high (33°C) room temperatures.

Figure 5

As the subjects began exercising, body temperature increased slightly under both normal and high temperatures. However, exercise at high temperatures resulted in a higher increase in body temperature from approximately 30 minutes onwards compared to that at normal temperatures. The longer the duration of the exercise, the higher the body temperature. At the end of the exercise, body temperature had risen to more than 39℃ under high-temperature conditions; however, the temperature was about 38℃ under normal temperature conditions.

In other words, an exercise in these situations may lead to a faster increase in body temperature, which may worsen the damage to the abdomen. When you exercise in hot and humid conditions, do not forget to rehydrate yourself and take breaks frequently. Take responsibility for protecting your own body.

7) Yeh YJ, et al. Eur J Appl Physiol. 2013;113(6):1575–83

5. Summary

The following are the important points to remember about damage caused to the body during exercise.

  • ・Prolonged or intense exercise causes inflammation in the whole body and damage to the abdomen
  • ・If the body temperature increases or blood flow to the abdomen decreases, the ability to protect the abdomen decreases
  • ・Loss of abdominal defenses may lead to worse inflammation throughout the body
  • ・Exercising in hot and humid conditions makes the abdomen more susceptible to damage

Many people are not yet aware of the damage that can be caused by prolonged exercise or intense exercise. Exercising in hot and humid conditions, such as summer in Japan, is a time when our bodies are very susceptible to this damage.

Including the aforementioned explanation, take steps to ensure that you have sufficient knowledge of what sportspersons should know, that you undergo training that is considered appropriate even under difficult circumstances, and that you pay attention to your physical condition at all times so that you can achieve your desired performance.

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Supervising Editor:Masashi Miyashita


Masashi Miyashita
In 2006, he completed and was awarded a UK doctoral degree from Loughborough University, School of Sport and Exercise Sciences. After working in the positions of Research Associate in the Research Department of the Graduate School of Comprehensive Human Sciences at the University of Tsukuba, Assistant Professor in the Graduate School of the Faculty of Sports Sciences at Waseda University, and Associate Professor in the School of Art and Sports Science in the Faculty of Education at Tokyo Gakugei University, he started at his current position (Associate Professor at the Faculty of Sports Sciences at Waseda University) from 2016. His specialties include exercise metabolism, exercise physiology, exercise nutrition, and applied health science. His goals are developing an international joint research project and creating an international research base with the main themes of "exercise and postprandial metabolism" and "exercise and appetite adjustment".

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