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For the Canadian men’s soccer team, the road to qualifying for the 2022 World Cup led through the famously hostile atmosphere of Mexico City’s Estadio Azteca, built to bolster the nation’s bid to host the 1970 tournament. Visiting teams have long struggled with the thin air at 7,200 feet; in fact, much of the modern approach to altitude training and acclimatization emerged during preparation for the Mexico City Summer Olympics in 1968. But on this occasion the Canadian team turned to Michael Koehle, an environmental physiologist at the University of British Columbia, with a different concern: air pollution.
We’re all familiar with the idea that breathing dirty air is bad. It’s linked to elevated rates of heart and lung disease, diabetes, and even dementia. And there’s growing awareness that those of us who spend a lot of time breathing heavily in the great outdoors may be particularly vulnerable. In fact, more than a decade ago I interviewed Koehle, who is also a consultant with the Canadian Sport Institute Pacific and a team doctor with the Canadian track team, for an Outside article on this very topic. During exercise, he told me then, you suck in more air through your mouth, bypassing the filtering mechanisms in your nose and sending pollutants deeper into your airways. There’s good reason to think twice about working out in poor air conditions, but on the whole, he figured that the health benefits outweighed the risks. “Exercise is such a big hammer that it crushes everything else,” he told me.
That basic conclusion hasn’t changed, but in the past few years, air-quality concerns have intruded into our lives with greater insistence. The eye-opener for me occurred in the summer of 2021. As I finished a multiday hike in Banff National Park, smoke from a distant wildfire had reduced visibility to a few hundred yards. Until then I always thought air quality was a big-city issue, but it’s no longer possible to ignore even in remote wilderness. And as researchers like Koehle continue to tease out how exercise and air pollution interact, they increasingly find themselves fielding calls from athletes concerned not just about their health, but also about their performance.
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Earlier this year, Koehle collaborated with physiologists, physicians, and sports scientists from Canada, Spain, France, and Brazil to publish a consensus statement in the British Journal of Sports Medicine synthesizing current evidence on how to handle exercise and competition in polluted air. The data suggests that some forms of air pollution can have immediate effects on athletic performance, in addition to long-term impacts on crucial parameters like lung function; for example, a study published earlier this year found that elevated pollution levels slowed elite NCAA 5K runners by about 1.5 percent. The best solutions, of course, will need to address the sources of pollution and get a handle on climate change. In the meantime, here are some of the ideas that organizations like the Canadian soccer squad—which eked out a crucial draw in Mexico City—are deploying.
The simplest and most effective option is to minimize your exposure. To do that, you need to understand where and when pollution is at its worst, which you can do with real-time monitoring and forecasting tools, including Plume Labs’ air-quality app and the EPA’s AirNow site. “My message lately is that you need to consider the air-pollution recipe in your guidance,” Koehle says. In Tokyo at the 2020 Summer Olympics, for example, the expected ozone levels were roughly double the World Health Organization’s recommended peak-season threshold of 60 micrograms per cubic meter. In Qatar, which hosted the 2019 track and field world championships and the 2022 World Cup, the main concern was particulate matter—or PM for short—a broad category that includes motor-vehicle exhaust, wildfire smoke, and dust. Other pollutants, such as smog-inducing nitrogen oxides and pungent sulfur oxides, can add to the mix, depending on the location.
As researchers tease out how exercise and air pollution interact, they increasingly find themselves fielding calls from athletes concerned not just about their health, but also about their performance.
Early-morning workouts generally offer the best air quality, but your options later in the day depend on the details of the recipe. Ozone, which forms in sunlight, tends to be worst in the afternoon, while PM often follows traffic patterns, peaking after the evening rush hour. Ozone also spreads fairly uniformly throughout a given area, while PM is concentrated near its sources. Just 400 yards away from a major road, PM levels from traffic are negligible, offering a possible escape even during peak pollution times.
Among the newer ideas Koehle and his colleagues considered are the potential benefits of antioxidant supplements. Inhaling air pollution can result in harmful oxidative stress; exercise itself is a powerful antioxidant that seems to counteract some of that. This may be one of the reasons that both mouse studies and large epidemiological surveys have found that exercise in polluted air doesn’t seem to nullify the benefits of working out. That being the case, it’s reasonable to wonder whether bolstering your antioxidant defenses with a supplement might be even better. The research isn’t conclusive, but for ozone in particular, Koehle sees enough evidence to suggest trying 250 to 500 milligrams of vitamin C and 100 milligrams of vitamin E once a day for two weeks before a competition. The same logic might apply to warding off negative health effects like reduced lung function while traveling to a high-pollution destination, but Koehle doesn’t recommend staying on antioxidant supplements indefinitely, because there’s evidence, still hotly debated, that they can interfere with training adaptations.
An even more controversial idea is acclimatization—deliberately exercising in polluted air so your body will adapt to it and perform better when competing in similar conditions. There is some evidence that after a few days of exposure, irritant receptors in your airways become desensitized, mucus production increases (to help trap pollutants), and inflammation decreases. A 2018 analysis of college track results from 85,000 athletes found that those with higher ozone exposures in the seven days prior to a meet were less affected by high ozone levels during competition.
However, given the long-term health implications of pollution exposure, this is a topic Koehle approaches with caution. “Once you give some people a little permission, they overdo it and harm themselves,” he says. In practice, ozone levels tend to track with air temperature, so athletes working on heat acclimatization prior to a race probably gain some ozone acclimatization without trying to. That’s the approach Koehle suggested for the Canadian track team at the Tokyo Olympics, which spent two weeks in the muggy Nagoya suburb of Gifu prior to competing. Still, the evidence that you can acclimatize to PM is thinner than for ozone, and overall the technique seems like something to consider after you turn pro.
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In comparison, the idea of minimizing pollution exposure by wearing a protective mask seems almost uncontroversial. There’s not a huge amount of research on the antipollution effects of masks during exercise, but an N95 or its equivalent could be useful for lessening before-competition exposure in places with a lot of PM, such as sitting on a team bus in traffic. Some data suggests that prior exposure to air pollution can have a delayed effect on breathing and performance, even if the competition itself takes place in clean air. Pollution is a 24-hour-a-day issue, Koehle points out, not just something to worry about once your workout starts.
For most of us, of course, the primary concern is health rather than performance. The morning after that hike in Banff, I remember waking up in a nearby motel to ominous warnings against doing any sort of outdoor exercise. There’s no simple answer for how to balance the conflicting health risks of inactivity with the inhalation of pollutants; what’s clear is that it’s worth taking whatever steps you can to minimize your exposure. It’s also worth remembering Koehle’s take—that exercise is generally the bigger hammer. Personally, I headed out early for a short jog along the river.
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