Why do people feel tired? Explain it with biology.

Fatigue, also known as fatigue, is a state in which the body's ability to work decreases after continuous work. It first occurs in the cerebral cortex. When the same work is repeated for a long time, the cells in the cerebral cortex are frequently stimulated and produce strong excitement. To a certain extent, excitement will turn into inhibition. If you continue to work, this inhibition process will be strengthened, leading to fatigue. If the human body is in a state of fatigue for a long time without proper rest, fatigue will accumulate and produce "excessive fatigue". In severe cases, the functions of the central nervous system and other body systems will be out of balance, which will affect learning. Proper rest is an important means to eliminate fatigue. Rest methods can be divided into static rest and active rest: static rest: sleep is the most effective static rest method to eliminate fatigue. People should have a certain amount of sleep every day so that all systems and organs of the body can rest.

Active rest: refers to "changing activities" to eliminate fatigue. For example, after thinking for a long time, we should do some physical activities instead, and do consistent lower limb activities after upper limb activities, because the excitement generated by the latter activities can inhibit the excitement generated by the former activities and make the excited cells of the former rest.

Proper physical activity is an effective way to eliminate fatigue, so you should take part in it often. There are many methods to choose the best amount of exercise, such as index evaluation, heart rate evaluation, Cooper evaluation, fixed evaluation, fatigue evaluation, simple evaluation and stage evaluation. Because everyone's actual situation is very different, the difference of quiet heart rate is 15-30%, or even more, so choosing the best amount of exercise depends on your age, gender, professional characteristics, physical condition, health level, sports foundation, living environment and goals and tasks. In order to let everyone learn how to choose the best amount of exercise, here are some typical international methods (calculation formulas):

(a) index evaluation method index evaluation method; It is a method to compare and evaluate the physiological load index. The specific method is to measure the exercise heart rate every 2-5 minutes, and record the heart rate measured every time (based on the heart rate of 1 minute) until the end of the exercise. Firstly, the average heart rate during exercise is obtained, then the quiet heart rate is divided by the average heart rate, and the obtained value is compared with physiological indexes to evaluate the amount of exercise. (2) Heart rate index method The heart rate index method refers to the number of times that the heart rate should reach per minute during exercise. American physiologists believe that it is a simple and effective method to select and evaluate the best amount of exercise by using the heart rate during exercise. Calculation formula: (3) Cooper's evaluation method Cooper is a well-known field of physiology in the United States. The best exercise heart rate formula he studied is representative, so it is widely adopted by countries all over the world. (4) Simple evaluation method Simple evaluation method is to subtract the age difference with different constants, which is the best exercise heart rate.