The weather is too cold.

Running before dawn in winter morning is not good for the following reasons:

(1) violates the laws of nature and interferes with the normal operation of human biological clock.

The ancients said that when the sun rises, they rest at sunset, and when they rest, they exercise when they exercise, following the laws of nature, which is the guarantee of human health. Running before dawn obviously does not conform to the scientific concept.

(2) The air quality is not good.

Before sunrise in winter, the ground temperature is low, and the content of pollutants such as carbon monoxide and carbon dioxide released in the air is high. Exercise in this environment will seriously damage your health.

(3) The temperature drops too fast, the pathogenic microorganisms of upper respiratory tract infection are active, and the stimulation of cold air is easy to induce angina pectoris.

In short, although running and morning exercises in winter can enhance immunity, outdoor activities are not as early as possible. Health experts suggest that outdoor fitness in winter should be after sunrise.