It's cold and dark outside, and your bed is so warm and comfortable. Going for a run seems like such a bad idea. But before you hide your running shoes, it might be worth giving that crazy idea a go.
According to The Huffington Post, an outdoor run in winter, as opposed to one on a treadmill（跑步机）, burns more calories because the body is working hard to regulate（调节）its core temperature. Furthermore, research shows that race times are faster in cold weather than in warmer temperatures—and quicker runs burn more calories. Similarly, cold weather also makes the heart work harder to distribute blood through the body, making that vital muscle even stronger.
Outdoor exercise also turns up your energy and rids you of the stress and depression that build up every day. The heat and humidity in the summer can drag you down and tire you faster, but cold weather is refreshing. It adjusts you to your surroundings, making you feel alive.
Of course, the threat of smog in some built-up areas is a further obstacle to winter exercise. Heart attacks, lung cancer, stroke and asthma are all dangers of running in smog. Exercise in air pollution increases the potential problems. If you do choose to run outside on smoggy days, take a path in a park or residential area to avoid car exhaust（尾气）, and go early in the morning, before rush hour. But staying inside on smoggy days and waiting for the next clear day to run is best.
