The time period of morning running is usually from 5 am to 7 am. Morning running can quickly wake up the body organs that have slept all night and accelerate metabolism. After running in the morning, it can generally bring athletes plenty of energy all day. But it will also increase the burden of cardiovascular and cerebrovascular diseases. Moreover, the air quality in cities is generally not good enough. If you exercise too early, too much smoke and carbon dioxide in cold air will be harmful to people's health, and cold air may also cause damage to joints.