When air quality is poor—for example, from wildfire smoke—we’re advised not to exercise outdoors. Let’s talk about why, and what you can do instead.
You breathe more when you exercise
Exercise is a particular problem during smoky days because exercise simply makes you breathe more. The harder your body works, the more oxygen you need, and so the more air you’ll have to suck in to get it.
Many components of polluted air are bad for our health, but among the most problematic are PM2.5 particles, those smaller than 2.5 microns. (By comparison, dust and pollen tend to be in the PM10 category, ten microns and under.) These small particles can reach deeper into the lungs. Smoke or polluted air that contains a lot of PM2.5 particles can cause irritation to the eyes, nose, throat, and lungs, and can cause coughing and shortness of breath.
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Indoor air tends to be cleaner than outdoor air
When air quality is poor, it’s usually outdoor exercise we’re warned away from. But the air quality indoors can vary.
Some houses—especially newer and more energy-efficient ones—do a good job keeping indoor air separate from outdoor air, while other houses are leakier. If your house is older or if you’re in the habit of keeping windows open, you may have plenty of particulates indoors as well. Closing windows, using appropriate vents on your air conditioners, and using an air purifier can help.
This means that indoor exercise pretty much always beats outdoor exercise for air quality, although if the indoor air is bad enough it may still irritate your lungs. Now is a good time to figure out workouts you can do indoors, whether that’s a YouTube video or hopping on a bike trainer. That said, on the worst days, it may be best to just take a rest day and wait for the air to improve.
How bad is too bad to exercise?
There’s not a clear, black-and-white answer to this question, but here are some guidelines.
First, if the air quality index (AQI) is 50 or lower, the benefits of exercise may outweigh the risk of pollution. A study conducted in 2016 and discussed here in Outside suggests that short sessions of exercise are fine at this level. For more detail, the Yolo-Solano air quality management district in California has a chart to help you decide what exercise is appropriate at different AQI levels.
Above 200, they say, you shouldn’t exercise outdoors at all. Between 151 and 200 (“unhealthy for everyone”), any exercise done outdoors should have plenty of rest time, and it would be better to bring things indoors if you can. Between 100 and 150 (“unhealthy for sensitive groups”) short activities outdoors are considered okay, and team practices or workouts should be at a reduced intensity. Below 100, the chart deems it a “good day to be outside.”
Know if you are in a “sensitive group”
If you’re in one of those sensitive groups, though, the chart advises that you should keep an eye on your symptoms as the air quality deteriorates. Very young and old people—under 12 or over 65—are among the sensitive groups. People who have asthma or lung conditions, and people who are pregnant, should monitor their symptoms and reduce their outdoor exercise even if those around them seem to be fine.
Allergist and pulmonologist R. Sharon Chinthrajah told Medscape that she’s adjusting some patients’ medications and action plans, and asking them to get in touch if they are having more trouble than usual breathing. If you have a lung condition or fall into another of the sensitive groups, you may want to check in with your doctor about how you should handle the increased health risks of wildfire season.
Air quality matters all day, not just when you’re exercising, so spending time in clean air and even wearing an N95 mask can help decrease the overall amount of particulates you’re breathing in. While cloth masks don’t protect anywhere near as well as respirators, Chinthrajah told Medscape they may be better than nothing.