Environment Canada issued an air quality warning on Wednesday, after smoke from the wildfires in northwestern Ontario plummeted Toronto’s air quality to the worst in the world. By Thursday morning, only Detroit had worse air quality than Toronto, according to IQAir, a Swiss air quality technology company that operates the world’s largest real-time air quality information platform.
With conditions not expected to improve before Friday, we look back at this interview with exercise physiologist Ira Jacobs from 2023 when the air quality in Toronto was similarly polluted due to forest fires in Quebec and Ontario.
A professor emeritus at the University of Toronto Faculty of Kinesiology and Physical Education, Jacobs' area of expertise includes physiological responses and adaptations to environmental extremes.
What are the risks of exercising outdoors when the air is smoky from wildfires?
The main issues of concern are the absolute amount and size of the particles in the air that are associated with both acute respiratory health risks, as well as accumulating increases in those risks with repeated exposures.
The other important aspect is our body’s ventilation rate —— how much air is being drawn into our lungs. The health risks are compounded because most of us become primarily “mouth breathers” when we exercise, so some of the body’s natural particulate trapping and filtering mechanisms in the nasal cavity become ineffective at the high ventilation rates that we generate during exercise - at least 10 times the normal resting ventilation rates, and much higher for athletes who are training or competing.
What’s a good alternative to outdoor exercise?
Much of the problem is avoided or significantly reduced by exercising indoors, particularly in more recently constructed buildings that are well sealed and where the indoor air is recirculated and cooled as part of the recirculation process. Some older large buildings draw in outdoor air continuously and cool it after it has been drawn into the building, so it’s good to know what the status of the air circulation is wherever you’re exercising indoors given today’s air quality challenges. Even in this worst-case scenario (for exercising), appropriate filters can be installed to trap the smoke particles that are less than 2.5 microns in size (about 40-50 times smaller than a grain of sand). In summary, for now and until the air quality index improves, exercise in a central air-conditioned building or home.
For those not easily dissuaded, are there any adjustments they can make to reduce the risks such as shortening the length of the exercise, doing it slower or wearing a mask?
Yes, reducing the duration of exercise at high ventilation rates will commensurately reduce the risk.
And, yes, wearing a respirator like a N95 respirator that traps particulate matter that is less than 2.5 microns in size is also effective, but admittedly not very pleasant on a warm day. And some people find that a respirator or any face mask seriously impedes the ability to maintain the kind of exercise intensities that high performance athletes need to maintain their training effects.