Because the air is not fresh at 5 a.m. and is not favorable to the respiratory system, running at 5 a.m. is generally not recommended. The sun has not yet risen at 5:00 a.m., and the carbon dioxide in the air is not completely absorbed by plants and contains a large amount of carbon dioxide. Some areas may also be hazy, in the process of running will inhale too much not fresh air, easy to affect the respiratory function, which will lead to coughing and poor breathing and other performance. Moreover, the sun has not yet risen at 5 a.m., and visibility is low, making it easier for falls to occur. Although running in the morning has certain benefits to the body and can exercise the body, but also need to choose the right time. It is recommended to try to choose to run in a fresh air environment, fresh air is more conducive to the respiratory system. If you feel unwell, you need to go to the hospital in time.