USC Health Now

Q. Is there an optimal time for outdoor exercise in regards to smog?

A: Longer daylight hours may lure you outside to exercise in the spring, but rising temperatures often mean smoggier air conditions, which can make breathing difficult during exercise. According to environmental expert, Ed Avol, M.S., clinical professor of preventive medicine at the Keck School of Medicine of USC, avoiding busy roadsides and exercise during peak smog hours may be beneficial in the short- and long-term to all levels of athletes. “The best times to work out are during the morning or in the evening and away from traffic. The afternoons usually have the highest concentration of the air pollution we know as smog,” says Avol. “Working out in smoggy conditions can cause a burning sensation in the chest, coughing and difficulty breathing. These symptoms can be relieved by avoiding peak times of smog exposure and by avoiding noxious car exhaust.” Professional athletes have to be even more mindful of air quality during training. Avol warns that competitive athletes have very high ventilation rates and breathe in lots of outdoor air. “They especially need to be mindful of air exposures because their lungs are like vacuum cleaners that trap the pollution particles. ”