1. From the human body itself. Sports medicine has proved that when you get up in the morning, the operation of various organs of the human body is still at a low level, because every function of the body will be reduced to the lowest state when you sleep, thus reducing consumption and getting full rest. Going to exercise immediately after getting up is the same as not preparing to warm up before strenuous exercise to make your body fully active. At this time, exercise is more dangerous for people with weak cardiovascular function. The activity ability of human body is fully developed at night. Running at this time makes it easier for the body to adapt to the rhythm of exercise. Running at night, as long as you master the intensity of exercise, will make people sleep better.

2. From the external environment, the carbon dioxide index in the air is the highest in the morning, which is the result of interaction with photosynthesis and respiration of plants. Because there is no sunshine at night, plants can hardly carry out photosynthesis, but respiration is always going on, so plants have been consuming oxygen and producing carbon dioxide at night, and this situation continues until the dawn when plants can carry out photosynthesis. So in the morning, the oxygen content in the air is low and the carbon dioxide content is high, which is not suitable for exercise. At night, on the other hand, it can be said that the oxygen content is the highest and the carbon dioxide content is the lowest in a day. And the dust suspended in the air the day before has not completely disappeared. At this time, exercise is far less good than the environment at night. Moreover, exercise in the morning is not conducive to human immune function. After morning exercise, the human body produces too much adrenocortical hormone, and the content of adrenocortical hormone in the body increases. This not only can not enhance physical fitness, but also often leads to high blood pressure due to corticosteroids, and also inhibits the normal immune function of the human body. There is no such worry when doing physical exercise at night, because the content of corticosteroids at night is significantly lower than that in the morning. The harm of morning exercise does not stop there. After morning exercise, the speed of saliva flow will obviously slow down, because saliva flow can help people resist infection. If saliva flows slowly, it will make people more susceptible to the virus. To sum up, we can see that not only do we not get enough exercise in the morning, but we also have shortcomings such as easy injury and decreased immunity, while evening exercise can not only avoid these shortcomings, but also greatly improve the exercise effect and improve the quality of sleep. Therefore, evening exercise is much more scientific than morning exercise.