Why can children “charge for 5 minutes and play all day”?

  Why are children so energetic that they don’t want to go home after playing until dark every day? Today we will analyze the reasons for children’s tirelessness from their physical structure and mobility.
  Children’s extraordinary vigorous energy is largely related to their physiological and neuromodulation characteristics that are not easy to fatigue. In fact, since the middle of the last century, people have begun to study children’s bones, muscles, and sports metabolism. The research on children’s sports ability is still concerned by scientists.
Compared with adults, children’s muscles are more resistant to fatigue

  Children not only have muscles with stronger anti-fatigue ability, but also have the ability to recover very quickly after heavy exercise. A study by French scholars in 2018 adopted the following method.
  Three groups of people were selected as the research objects, namely ① children aged 8-12, ② adult men who do not exercise at all, and ③ durability athletes (professional long-distance cyclists and triathletes). The three groups of people did bicycle exercises to determine their energy production and recovery after exercise.
  The fast-twitch fibers in muscles are mainly powered by anaerobic metabolism and have the characteristics of large output power and easy to fatigue; slow-twitch fibers are mainly supplied by aerobic metabolism, with low output power but strong anti-fatigue ability. The anti-fatigue degree of muscles is related to its metabolism.
  Through a 30-second high-intensity short-term anaerobic exercise test period, the researchers obtained the energy output of the three groups of people (also called fatigue index, the higher the output energy value, the easier it is to fatigue).

The graph of the heart rate changes of children and adults after strenuous exercise and light exercise.

  It can be seen from the figure that during the test period, the energy output of prepubertal children was 35.2% and 51.8% less than that of the athlete group and the ordinary adult group, respectively.
  In other words, the fatigue of children is much lower than that of adults. This result also indirectly shows that children’s anaerobic metabolism is lower than that of adults, so they are less prone to fatigue.
Children recover faster after exercise

  Looking at the recovery after exercise, the data in the following figure shows that the heart rate of pre-adolescent children starts to recover in 30 seconds. Although professional athletes also start to recover in 45 seconds, the recovery speed of children is significantly faster than that of adults. In addition, children and endurance athletes have similar rates of decline in oxygen uptake after exercise.
  The tirelessness of pre-adolescent children is usually associated with less accumulation of metabolic byproducts (ie hydrogen ions, lactate, and inorganic phosphate) produced in the muscles during exercise.
  Lactic acid is produced by short-term high-intensity anaerobic exercise that relies on glycolysis to provide energy. As a strong organic acid, lactic acid will produce hydrogen ions when it dissociates, causing the PH value of the muscle to drop. The accumulation of hydrogen ions can also interfere with the binding of calcium ions and troponin, thereby interfering with the process of muscle contraction and causing fatigue. Children can clear lactic acid from the blood faster, making them less prone to fatigue.
  There are also pediatric literatures showing that pre-pubertal children have low anaerobic metabolism and low glycolytic energy conversion rate. Therefore, in addition to fast metabolism, the concentration of lactic acid accumulated in the blood and muscles of children is also low, so it shows Higher resistance to fatigue.
  In addition, pediatric researchers also specifically analyzed the changes in children’s heart rate before and after exercise. The researchers conducted experiments on 9 children aged 9 to 12 and 8 young people, letting them perform short-term high-intensity exercise and continuous low-intensity exercise respectively, and tested the children’s heart rate recovery within 4 minutes after exercise. As a result, whether it is high-intensity exercise or low-intensity exercise, children can quickly restore their heart rate.
  Humans have a circadian rhythm. When the biological clock reaches a certain time, it tends to enter a state of sleep or wakefulness. Our heart rate also has a circadian rhythm.
  In the human body, there is a nervous system that specifically regulates the circadian rhythm of the internal organs. It is divided into two types: sympathetic nerves and parasympathetic nerves. The sympathetic nerves mainly innervate our visceral activities when we are awake. On the contrary, the parasympathetic nerves innervate our visceral activities during sleep.
  For the heart, in order to keep us awake in the morning, the sympathetic nerve activity is active and the heart rate increases, and the heart rate decreases due to the parasympathetic nerve dominating during sleep. In the early stage of heart rate recovery after high or low-intensity exercise, although consciousness is still awake, this stage is mainly controlled by parasympathetic nerves.
  Compared with adults, children have stronger parasympathetic regulation, which helps them recover faster and slow down their heart rate. At this time, young adults still maintain relatively high sympathetic nerve activity, that is, the heart is awake, which results in a significant delay in heart rate recovery.

The rate of recovery of the resting heart rate of preteen children, untrained adults and well-trained adult endurance athletes after exercise.

The power output process of preteen children, untrained adults and well-trained adult endurance athletes over time.

  In addition, due to the immature development of various organs in children, if children do not recover their heart rate as soon as possible after exercise, it may cause excessive heart fatigue. Therefore, children protect their small hearts from overload after frequent exercise by enhancing the regulatory function of the central parasympathetic nerve.
  Children and professional athletes have very similar muscle structures. Generally speaking, sports experts divide acute fatigue during exercise into central and peripheral ones. Central fatigue involves the brain or spinal cord of the central nervous system, while peripheral fatigue is mainly related to muscles and also includes other body organs such as the heart and lungs.
  There is a complex interaction between peripheral and central fatigue. For example, the central nervous system will feed back muscle fatigue during exercise and limit the speed of exercise to help prevent premature fatigue.
  Researchers from the University of Clermont-Auvergne in France published a study titled “Children show more neurological fatigue characteristics than endurance athletes and untrained adults.” This study proved for the first time that children experience less peripheral (i.e. muscle) fatigue during high-intensity exercise, and show slightly higher central (i.e. nerve) fatigue than untrained adults. When central fatigue occurs in the human body, the central nervous system You can limit the intensity of exercise to prevent muscle damage and fatigue.
  Professional athletes are well-trained in endurance and can complete 10,000 meters in 28-33 minutes. Although children cannot complete such competitions, the various data mentioned in the previous article show that children and the above-mentioned well-trained adult endurance athletes are very similar in fatigue and heartbeat recovery during exercise, and even children perform even more. excellent.
  This result occurs because children and professional athletes have very similar muscle structures (such as muscle fiber percentage, etc.), which can reduce the damage to muscle strength. This is also the reason why pre-adolescent children can repeat high-intensity exercises after a short rest when most adults are tired.
  The above research results have guiding significance for the development of children’s potential athletic ability. The aerobic capacity of children’s muscles is similar to that of young people, but their anaerobic capacity is lower than that of untrained adults. Therefore, stimulating the anaerobic adaptation of young athletes by using shorter, higher-intensity anaerobic exercise training in training is more beneficial to the development of their sports function.
  In addition, these studies also allow the public to understand how our bodies have changed from childhood to adulthood. Researchers speculate that the loss of muscle aerobic capacity from childhood to adulthood may have undesirable health consequences. Therefore, aerobic exercise training is recommended to maintain our health.
  In addition, the prevalence of metabolic diseases, including diabetes and many forms of cancer, is increasing in young people, but they are still rare in children. Therefore, exercise training to maintain “childhood muscles” may be an effective way to prevent diseases and maintain health.