Life lies in exercise. I think this sentence is familiar to everyone, especially the elders. On weekdays, they always talk about these topics: "Don't lie at home every day, going out to exercise is good for your health", "You are prone to catch a cold, and your health is bad because you don't like sports" and "If you are too fat, don't go to exercise at once". This concept is almost deeply rooted in the hearts of the people. People with weak constitution hope to enhance their immunity through exercise, while the elderly hope to prolong their life through exercise. It is said that "exercise can improve immunity". Why do I love sports and catch a cold more easily? What is the relationship between immunity and exercise? Exercise immediately after exercise can't improve immunity. On the contrary, after the intensity of exercise exceeds a certain threshold, not only will the immunity decline within 2-4 hours after the activity stops, but it will also enter a period called window opening period. If immunity is a barrier to protect the human body, then the immune barrier opens a window during the window opening period, during which immunity is worse than usual, which is the weakest moment of the human body.