Colorado and the west coast have faced devastating fires this year. In addition to the deaths and destruction that are a direct result of the fires, there are residual health impacts for millions of people both near and far from the actual flames. For people who are physically active, air quality is a pressing concern, and many questions are being discussed, particularly on social media. Is it safe to exercise outside? At what air quality is it too risky to do so? Should I slow down or change the duration of my workout? Is it a lot safer to exercise indoors or is indoor air quality also impacted by fire smoke? With many questions and few clear answers, we will try to break down recommendations and guidelines regarding exercising in areas where there is wildfire smoke in the air.
Should I exercise outside?
We know that several components in wildfire smoke, especially particulate matter, can be harmful to your health. A little air pollution science: particulate matter is made up of tiny pieces of solids or liquids that are in the air. These include dust, dirt, soot, or drops of liquid. Some are big enough to see, others are too small to see in the air. Bigger particles, called PM10, usually arising from dust from roads, farms, dry riverbeds, construction sites, etc. are types of PM10 and can irritate your eyes, nose, and throat. Wildfire smoke contains many smaller particles, called PM2.5, which are more dangerous because they can travel deeper into your lungs. Health risks include inflammation of the lungs and damage to blood vessels, potentially worsening cardiovascular disease (1).
Green to Yellow AQI
People who are exercising in areas affected by wildfire smoke should be paying attention to the local Air Quality Index or AQI. In addition to an overall AQI and a color-coded risk system, many municipalities break the AQI into components of ozone, PM10 and PM2.5. The Air Quality Index shown below provides some guidance for air quality and if/when to exercise outside. For most people, exercising in the green and yellow range (AQI up to 100) confers no issues although people who are very sensitive to air pollution may start to experience issues as the AQI rises toward 100.
In the orange range (AQI = 101-150), “members of sensitive groups may experience health effects. The general public is less likely to be affected.” This is the area where some experts start to get concerned. It is probably the cutoff point if you know you fall into the “sensitive groups” category, e.g. those who have asthma, the elderly, and children. Some experts recommend that even healthy people should reduce overall exposure by exercising at a lower intensity or shorter duration, especially if you are having symptoms of irritation like sore throat or coughing (2). You might think that going slower would be helpful because you don’t breathe as hard when exercising at a lower intensity. Although there are no research studies that provide definitive evidence, studies done in a laboratory with humans exercising while breathing pollutants suggest that reducing the duration of exercise is more beneficial than lowering the intensity. If the choice is to slow your pace and spend more time outside or increase the pace and lower the duration, it might be wiser to go fast and short rather than slow and long. However, smoke exposure while working out for 20-30 minutes as compared to hours, will of course be less.
Red and Purple AQI
As the index increases to red (unhealthy), purple (very unhealthy), and maroon (hazardous), health risks increase as well. Few experts recommend hard outdoor exercise when the AQI is in the red category (151-200) and it would be difficult to find one who suggested it was a good idea when the AQI gets to purple (>200).
Stations may vary
Importantly, the AQI varies over the course of the day and even at different weather stations located just a few miles apart as local topography and wind conditions can have a dramatic effect on the number of pollutants in the air. You can check the weather stations in your area (usually by searching online for the AQI in your area) and making decisions on both where and when to exercise so that you can minimize your exposure to poor air quality. It also helps to exercise indoors when the AQI is high, in a relatively well-sealed indoor space with windows closed and air conditioner (or air purifier) running, the AQI is often less than half of the outdoor value. Naturally, during the pandemic, exercising indoors in a sealed space with other individuals is at odds with the recommendations to limit the spread of COVID, so exercising in your home may be a better option than a gym, depending on their safety measures.
Know before you go
If/when to exercise outside on days when there is wildfire smoke in the air is a personal choice. Knowing that visible smoke and haze means exposure to particulate matter (and even non-visible smoke contains potentially harmful PM2.5 particulates), it is recommended to check air quality regularly and to know whether you fall into a group that is sensitive to air pollution. Exercise is an important part of our healthy lifestyle, but it is also important to consider whether increased exposure to particulate matter on days with high AQI is actually counterproductive.
(1) https://www.cdc.gov/air/particulate_matter.html. National Center for Environmental Health Page last reviewed: September 4, 2019
(2) Reynolds, Gretchen. “Is it Safe to Exercise if the Air is Hazy with Wildfire Smoke?” New York Times. 23 September 2020, https://www.nytimes.com/2020/09/23/well/move/is-it-safe-to-exercise-if-the-air-is-hazy-with-wildfire-smoke.html?action=click&module=Top%20Stories&pgtype=Homepage&contentCollection=AtHome&package_index=2
(3) Air Quality Index (AQI) Basics, (2019, June 18) Retrieved September 15, 2020, from https://cfpub.epa.gov/airnow/index.cfm?action=aqibasics.aqi
Kimberly Burke is the director of the Adult Fitness Program at Colorado State University, an outreach program through the Department of Health and Exercise Science. Adult Fitness offers exercise opportunities for employees of CSU as well as community members, while providing hands-on learning experiences for health promotion students. To learn more see the Adult Fitness webpage.
Barry Braun, Ph.D, FACSM, is the head of the Department of Health and Exercise Science and executive director of the Human Performance Clinical Research Lab at Colorado State University.