This varies from person to person and also depends on your exercise goal. If you choose morning running, 1. Personally, I suggest not to exceed 5 kilometers, because his static heart rate is the lowest when he first gets up, and the exercise level of various organs of the human body is also in the lowest state, which is dangerous for people with poor cardiovascular function. 2. If your exercise goal is to lose fat. Then you can calculate your maximum heart rate according to your static heart rate, so as to control the appropriate aerobic time according to your heart rate range.