The more you practice, the more tired you will be. There are several reasons-poor rest and sleep, and exercise; When you are weak or sick, you can barely exercise; The amount of exercise exceeds one's capacity; Not used to it yet. Mainly due to lack of rest, long-term heavy physical labor, excessive exercise, overeating and so on. The human body will be overloaded and its immunity will decline. There is a question of "degree". How to master "moderation" is related to the success or failure of exercise. Exercise can not only strengthen the body, but also harm the body. Insisting on physical exercise is an effective means to improve the body's immunity. Exercise can promote the internal circulation and endocrine of human body, and make the functions of various organs of human body at a higher level, thus effectively improving the immunity of the body. When exercising, we must pay attention to moderation, continuity and step by step, so as to avoid excessive interval or intensity of exercise, which will lead to physical fatigue, decreased immunity and drowsiness after exercise. There are many factors that cause the decline of human immunity, among which overwork and insufficient exercise are the main reasons. Overwork has a bad effect on the autonomic nervous system, thus affecting the endocrine system and immune system, leading to a sharp decline in human physical strength for a period of time.