DENVER (KDVR) — Smoke from wildfires in Canada is blowing into Denver and causing poor air quality.

According to IQAir, Denver ranked in the top five for worst air quality in the world on Friday. Fortunately, rain and wind direction should help the air quality before Sunday’s marathon, but doctors suggest avoiding any last-minute training on Friday.

“If you ordinarily run 3 or 4 miles and don’t have any trouble and you’re out there running today, kind of in your last tune-up for the marathon, and you’re having a lot of trouble breathing, we’d say probably stop you’re run,” said Dr. Anthony Gerber, a pulmonologist and air quality expert with National Jewish Health. “If the breathing is bad enough you might even have to have someone look at you.”

Gerber said his best advice is to listen to your body. If your breathing becomes extra strained, it might be a good time to stop.

“If you’re running out here and breathing isn’t good, your chest feels heavy, the advice would be you should probably stop. If you’re having those kinds of symptoms, I think that your long-term health is more important,” Gerber said.

Gerber said people with asthma or lung disease will experience it the most, but others might also feel similar symptoms with this type of air quality.

“Even 70-year-olds who are training for marathons, they might have heart disease, cardiovascular disease, so those folks, again, we’d say you’ve done all your training, you got the big health benefit already, maybe skip the race if the pollution is as bad,” Gerber said.