This is the eternal question I’ve been facing for a few years. Okay, air quality is bad. Should I postpone my running session, will it be better in the next hours, in the next days, should I run indoors, should I wear a mask? Is it worse not exercising at all or exercising when it’s polluted?
The first time I ever considered the pollution level to decide whether and when to go running was during summer in 2018 when I was living in Paris. France was going through a heat wave (as every summer now), and the capital city was in an ozone alert. I was hearing and reading everywhere to avoid exercising outside because of irritation, respiratory and cardiovascular risks. I remember having gone running at night around 9pm (it was still abnormally hot), hoping to avoid the pollution peak and breathing through my nose (which was quite challenging in the hilly parc des buttes Chaumont).
Unfortunately, this has not been my only experience of air pollution. I really started to study the issue after moving to Hanoi, which was often ranked in the top 5 of the world’s most polluted cities. I continued facing alarming pollution levels in Kampala, in Dakar, and to a lesser extent, in Casablanca.
So should you give-up running in a polluted city? Here are tips to survive without sacrificing your favourite sport, based on my humble experience. Let’s go!
Is running aggravating the health effects of pollution?
Disclaimer: I’m not a scientist nor a health professional, this is just a compilation of what I found about the subject.
I will try not to be too long, but it is essential to know some basics on the health effects of pollution (to avoid running next to the traffic jams like Ugandans do, especially when the cars date back from the 90’s).
We can classify pollutants in two categories: PM10 and PM2.5, which differentiate the fine particulate (Particulate Matter) in suspension in the air. PM10 are 10 microns or smaller and PM2.5 2.5 microns or smaller. The smaller the particle the harder to filtrate, the deeper it can enter into your lungs and the most dangerous it is. They mainly come from exhaust fumes, industries, charcoal and wood burning (many people in Asian and African countries are still cooking with charcoal, people in Northern countries heat their house with chimneys).
What are the health risks associated with pollution?
- Respiratory issues: on the short term, high level of pollution favours the development of respiratory symptoms such as cough, asthma, lungs irritation. On the long term, exposure to high levels of fine particles increases significantly the probability of developing lung cancers (by 22%, according to this study). That’s why WHO has classified air pollution as a definite human carcinogen.
- Cardiovascular diseases (CVD): researchers have shown1 that high level of PM are linked to higher risks of suffering from CVD such as thrombosis, stroke, heart attack… This is because fine particles would favour a stiffening and a reduction in the diameter of the arteries.
And what about running (I hear you think)?
Well the good news is, physical activity, most of the time (understand: in a not-too polluted environment) reduces greatly the risks of having CVD and respiratory issues (phew!). The thing is, when it comes to environments with a high concentration of pollutants, studies are scarce and somehow controversial to determine if physical activity at moderate or high frequency (like running) is reducing or amplifying these risks. In other words, do the positive effects of running compensate the negative health effects of air pollution, or on the contrary, does physical activity aggravate them?
Aerobic activity, including running, expose you to air pollution at a higher degree since: you will breathe much more frequently and inhale a much greater quantity of air, you will breathe deeper causing the particles to enter deeper into your lungs, and you will breathe (most of the time) through your mouth, whereas the nose can already filter some of the biggest particles. Hooray! And these effects are greater among women runners (double hooray!)
So can the harmful effects of pollution cancel or outweigh the benefits of aerobic activity? The debate is still open. A study carried out by Hong Kong researchers2 in 2019 did not find any causality between physical activity and negative health effects in polluted environment. Physical activity would be beneficial independently of air quality. However, the latest study published in 2021 by Korean researchers3 does demonstrate that for young adults (20-39 years-old) exposed to high levels of air pollution (49.92 and 26.46 μm/m3 or more for PM10 and PM2.5 respectively), an increase of physical activity “to more than 1000 MET-min/week, which is more than internationally recommended levels for physical activity, could adversely affect cardiovascular health (MET = “metabolic equivalent task”). This is an important result suggesting that, unlike middle-aged people over 40, excessive physical activity may not always be beneficial for cardiovascular health in younger adults when they are exposed to high concentrations of air pollution.” On the other hand, the study shows that an increase in physical exercise in a low to moderate polluted environment reduces the risk of developing CVDs. Researchers conclude that when levels of pollution are high, doing more exercise than recommended (500-999 MET-mins/week according to the European Society of Cardiology) “may offset or even reverse the beneficial effects”.
Good news, 1000 minutes of physical activity per week leaves a good margin for exercising. Indeed, even if it includes not only sports like running, cycling (even slowly), but also walking at a brisk pace, most of us (amateurs running aficionados) would probably not exceed those 1000 min/week. For example, even if I walk to work around 45 min a day 5 days a week at a brisk pace, add two running sessions and an hour swimming plus two or three sessions of muscle strengthening/workout (provided that counts as MET), I stand myself around 500 MET-min/week (phew again!)
Anyway, even if causality between air pollution, aerobic activity and increased risk of cardio vascular and respiratory diseases are still not that clear, let’s be careful and protect ourselves. Living in a polluted environment remains detrimental in any case, physical activity or not.
So what’s the plan?
Running in a polluted city: tested solutions
Pollution monitoring
I would say that your first reflex when you live in a polluted city is to check the pollution level before going running. Back then in Hanoi I was updating the data a hundred times a day to know if I could go, from 7am to 10pm, and I I was doing the same in Kampala (“only” ten times a day though).
Where to find pollution data? The website IQAir and its corresponding mobile app provide air pollution data in a great number of countries worldwide, from many different local contributors. The score displayed is the result of the addition of PM2.5 and PM10. You can pin your favourite places on the homepage, share your location to get the nearest data, and configure your different environments (home, work, outdoor environment) to monitor your daily exposure to pollution. IQAir also provides recommendations (close your windows, don’t exercise, etc) and a real-time ranking of the world’s top polluted cities (why is Hanoi so high while Saigon is always moderate 😒). However, when you live in a small city and/or in some parts of the world (understand: Africa), they are fewer contributors and data sources (often only the US embassy) and the data is not updated so often. In this case, IQAir provides satellite estimation of air pollution, which is not as accurate as data collected with sensors.
I’m lucky that in Uganda, a local project headed by Makerere University is providing real-time air quality data, via the mobile app AirQo (edit July 2023: data from AirQo sensors is now integrated in IQAir!). There are already many sensors deployed in Kampala, and a few in regional cities, but they are expanding quickly to other African cities, including in Nairobi, Accra, Bujumbura and Lagos. How do I use it? Well in Kampala, you can actually assess the pollution level by looking out of your window. If the “fog” is so thick that you can’t see the neighbouring hill, that’s no good sign. Anyway, I always check the pollution level of my running zone a few hours and minutes before: if it’s orange, red (or purple 😢), I don’t go! The same applies for swimming, as I was swimming outdoors.
Timing, route, session
These may look like basic and obvious recommendations, but worth reminding.
In general, avoid traffic peak hours, say 6:30/7am-9am and 5pm-7pm. Easy to say, harder to apply (I know!) when you’re working the whole day. If you can run at lunch break, if you’re a (very) early bird or if you can make it in the evening (but not too late!), those are probably the best options. In Kampala, Sundays are perfect because the traffic is low, and so is pollution. Otherwise, during the week, I’m often going after work, i.e around 6pm 😕.
You may think the best idea should be to go running during the night. Indeed, the traffic is lower, and so is the temperature. But in very polluted cities, you can often actually notice an increase of the air pollution level as soon as it gets dark. Why? First, because as the temperature decreases, the air gets stuck at ground level (whereas with heat, the air goes-up and get mixed4). Second, because most plants stop photosynthesis in the absence of light, i.e they don’t absorb CO2 anymore to produce oxygen. Third (this depends on the city, but in Hanoi it was the case), many heavy trucks are on the roads and construction works happen during the night.
Concerning the route, it is worth avoiding at maximum the large avenues with heavy traffic to favour small streets, or if it’s not possible (at some point sometimes you need to take these big streets), try to stay as far as possible from the cars. Indeed, the particles tend to rather stagnate around the zone where they have been emitted. Only by staying on the pavement (again, not always possible in African cities), you are already reducing the quantity of pollutants you inhale. And if you live in a city with hills, try to go up!
In terms of the session itself, running at a moderate intensity reduces respiratory flow and frequency, so forget about interval training on polluted days. Taking walking breaks can sometimes be necessary to reduce your breathing frequency. When I was running in Hanoi, I progressively learned to breathe through my nose (the nose filters the biggest particles and it’s a good way to ensure that you’re not breathing too deep nor too fast). You can try it at the beginning of your session, or when you are running down a slope, as a way to reduce your respiratory frequency. Again, easier said than done. You won’t run a 10K breathing through your nose overnight. It takes time and patience!
Wearing a mask
I know, it’s not the way we like to run. And not so fashionable (though it was funny to see the lack of understanding on the face of Ugandans I ran across). I wear my mask as a last resort, if we are going through a series of polluted days without windows of clean air on the horizon.
But all masks are not suitable and adapted for sports. First, it needs to be effective in terms of filtration of particles (forget home made covid masks and surgical masks, they’re completely useless). Choose a mask with N95 or N99 certification (which means that they filter respectively 95% and 99% of air particles, the equivalent norm in Europe would be FFP2 and FFP3, KN95 in China) that are adjustable to your morphology to be tight-fitting as possible to prevent air from coming in. The second criteria to choose your mask should be breathability. Most often, these masks have valves to facilitate breathing and ensure a more effective filtration. Of course, you won’t be able to run as fast as usual (forget about interval training or hill climbing sessions), as breathable as your mask can be, you will find it harder to breathe, you will be out of breath more easily, you will sweat more. Favour masks with two valves, that are made especially for sports, that allow you to easily remove (and change) the filter to wash the external part.
I have no recommendation for a specific brand, I use a Respro Ultralight and I’m quite happy with it, even if I use it more on a daily basis (walking to work, or when I take a moto-taxi for example) than for running (again, the best solution remains to go when the AQI is “reasonable”). I actually first looked for an effective, reusable pollution mask in general. If it could be used for exercising, so much the better. The mask is quite breathable (taking into account the high level of dust + humidity of Kampala), but even when walking, it’s not always easy to breathe through your nose (if one of your nostril if blocked, forget about it!). The advantage is that it does not have straps (our ears are suffering enough with face masks) but a kind of neck fastening to ensure a better fit. It’s quite an initial investment, but I’m still using the same filter six months later (even if I would have liked to replace it before, but well, Africa is not on the delivery map of course. And as long as you can breathe without difficulties it’s fine). A good advice then, is to stock-up spare filters in advance, depending on where you live, you won’t find them.
There are other good brands I have not tested, such as Base camp, Vogmask, Airinum, or Frogmask and R-PUR (Frenchies!).
Alternatives: swimming, treadmill, muscle strengthening?
Should we favour indoor training when the pollution levels outdoor are too high?
As usual, it depends. Swimming pools and gyms can be poorly ventilated. Avoid them if they are located close to a road or traffic spot. Finally, especially in developing countries (people don’t know about air pollution and how dangerous it can be), the windows are often open, which makes no sense! But if you can find a modern place a bit away from the traffic, then it can be a good option (even if, honestly, running on a treadmill is super boring).
Other option, take advantage from a break from outdoor activities to strengthen your core and legs muscles. Your running technique will be more efficient, and you will reduce the probability of injuries.
And you, what are your tricks to run in a polluted city?