For physical reasons.

First, compared with the air carrying a large number of vehicles at night, people's walking and breathing and a series of exhaust gases. The morning air is the air purified by a series of green plants in cities or villages. Relatively speaking, the air in the morning will be cleaner, with much less pollutants and more oxygen. So the morning air is good for the health of your lungs. But at night, there will be a lot of pollutants in the air at night because of the breathing of people who emit exhaust gas from vehicles during the day and the flying of some dust. As we all know, waste gas will affect the health of the lungs, which is not conducive to the circulation of the body to the whole body and is not conducive to the health of the whole body. From this perspective, people prefer to run in the morning.

Second, the lighting is not very good at night. If you run in the streets of the city, you may have an accident. For example, passing cars can't see funny people running well, which leads to some accidents. The other is a female teacher who was killed in fun run a few years ago. Running alone at night is not safe, because the crime rate will increase greatly at night. However, because there are not many people coming out at night, it is not convenient to call for help, and the field of vision is dark, which is not conducive to being discovered.

Third. Morning is the beginning of the day. If you do proper exercise in the morning, your body will wake up from a deep sleep as soon as possible. Maintain a good mental state for a day. However, if you choose the fun run in the evening, the evening is the time for people to rest. If you do it before the rest, you should do some physical exercise. It will make the whole body active and it is difficult to enter a state of rest and stability. It will eventually lead to the disorder of the biological clock. First, I didn't sleep very well. It will eventually affect your health.