Training and Exercising in Air Pollution: What Athletes Need to Know Before Smog Season
Across seven US marathons, every 10 µg/m³ rise in coarse particles (PM10) went with women finishing about 1.4% slower, on race days when pollution rarely broke national health limits (Marr & Ely, MSSE, 2010).
Food can't protect you from polluted air, and antioxidant supplements have only weak evidence, mostly against ozone rather than smog particles. What helps is timing and dose: check the AQI before training, move long or hard sessions indoors when the US AQI passes 150, avoid peak-traffic hours, and eat plenty of fruit and vegetables. Performance effects can build over weeks.
In Delhi, Lahore or Beijing in November, particle levels run many times higher than anything in that marathon dataset. North India's smog season runs from October into the new year, and wildfire smoke brings the same problem to California, western Canada and southeastern Australia.
Quick Overview
What does exercising in air pollution do to your body?
Exercising in air pollution raises the dose you take in. At rest you breathe roughly 6–8 litres of air a minute. In a hard run that can pass 100 litres, mostly through the mouth, which skips the filtering your nose does.
Fine particles carried that deep cause oxidative stress and inflammation in the airways and blood vessels, and fresh exhaust near busy roads looks more toxic than aged, diluted pollution (Rundell, BJSM, 2012). That's why the same AQI reading feels different on an arterial road at 8am than in a park two kilometres away.
Exercise in a polluted city still isn't automatically a net harm. At the global urban average for PM2.5 (22 µg/m³), the health benefits of cycling and walking outweigh pollution risk at any realistic amount of activity. At 100 µg/m³, a level common in north Indian winters, the harms of cycling overtake the benefits after about an hour and a half a day (Tainio et al., Prev Med, 2016). That modelling is about long-term health from daily travel rather than one session, but it shows where the trade-off tips.
If you have asthma, a heart condition, or you're recovering from a chest infection, your threshold is lower. Agree a plan for smog days with your doctor rather than working it out from an app.
Does air pollution slow athletes down?
Yes, modestly, and at lower levels than most people expect. Bundesliga footballers made fewer passes per match when particle levels near the stadium were higher, with effects at moderate concentrations that grew with player age (Lichter et al., Labour Econ, 2017).
The more useful finding for anyone training through a season comes from US college runners. Across 1,104 5km races, PM2.5 exposure over the 21 days before each race was linked to slower times: moving from 5 to 10 µg/m³ cost about 13 seconds (Cusick et al., Sci Rep, 2023). That window covers training as well as race-day air, at levels US apps colour green or yellow.
All three studies are observational, so they show association rather than proof. They still point the same way: weeks of hard training in dirty air show up on the clock, so manage exposure across the whole block rather than only on the worst mornings.
What AQI is too high to train outside?
On the US AQI used by AirNow, IQAir and most global apps, 151 is where the advice changes for everyone. From 151 to 200 ("Unhealthy"), healthy adults should cut back on long or heavy outdoor exertion and sensitive groups should skip outdoor exercise. From 201 everyone should reduce outdoor activity, and from 301 avoid it (American Lung Association, AQI guidance). Children, older adults, pregnant people and anyone with asthma should start cutting back from 101.
India uses a different scale, and this is where Indian athletes get caught out. US AQI 150 equals a PM2.5 concentration of 55.4 µg/m³ (US EPA, 2024). On India's National AQI the same concentration scores in the low 90s and is labelled "Satisfactory" (CPCB National AQI). An Indian reading of 150 sits in the "Moderate" band at roughly 75 µg/m³, air the US scale calls Unhealthy.
So check which scale your app uses. On the US scale, move long or hard sessions indoors above 150. On India's scale, treat 100 as your line. The two indices average and weight pollutants differently, so the conversion is approximate, but it's close enough to stop you running intervals in air you'd avoid if you saw the raw number.
When and where should you train in smog season?
Train away from traffic, at the cleanest hour, and for less total time outdoors when the air is bad. The Canadian sport medicine position statement on air pollution puts reducing total inhaled dose ahead of avoiding high intensity, and recommends checking hourly forecasts, staying off major roads and construction sites, and choosing parks or open routes (Hung et al., BJSM, 2023).
Timing depends on the pollutant. Ozone builds in sunlight and peaks in the afternoon and early evening, which is why summer advice in Los Angeles or Madrid says train early. Winter particle smog in north India behaves differently: cold, still air traps it near the ground overnight, and it often eases by late morning. The 5:30am run that works in March can be the dirtiest hour of the day in November, so check the hourly reading rather than following habit.
Indoors is usually better, if the room is. A gym with closed windows and decent filtration beats an arterial road; a packed, unventilated studio may not. The same statement suggests N95 masks for the commute and warm-up on high-pollution days rather than during hard efforts.
A workable smog-season week keeps easy runs and rides outdoors on cleaner days and moves intervals and long sessions onto a treadmill, trainer or indoor court when the AQI crosses your line. Judge those indoor sessions on effort, since pace and heart rate read differently.
Can food or supplements protect you from air pollution?
No. No diet or supplement has been shown to shield healthy athletes from particle smog. A review of diet and supplements against pollution-related lung disease found the evidence weak, mixed and mostly indirect, with no direct evidence that even a Mediterranean-style diet protects against air pollution (Whyand et al., Resp Res, 2018).
The narrow exception is ozone. The Canadian statement notes that antioxidant vitamins taken in the week before competition may reduce ozone-related falls in lung function (Hung et al., BJSM, 2023). That evidence is small, applies to ozone rather than winter particle smog, and doesn't justify a supplement plan. High-dose beta-carotene raised lung cancer risk in smokers, a reminder that antioxidant pills aren't harmless by default (Whyand et al., Resp Res, 2018).
Eat plenty of fruit and vegetables, whether that's guava, amla and palak dal in Delhi or berries, oranges and a big salad in Denver. They support general health and recovery. They aren't a filter.
The Fueletics Perspective
I'd rather an athlete lose a few outdoor sessions in November than carry three weeks of heavy exposure into a December race. Most of that cost is avoidable with an AQI check, a route change and a treadmill.
What goes wrong is the fuelling around it. A long run becomes a 40-minute indoor session at short notice, a treadmill run in a warm gym makes you sweat more than a cool winter morning would, and intake stays pinned to the original plan. Over a smog season that drift means under-fuelled indoor sessions or overeating on days that became easy. Your intake should follow the session you actually did, and those numbers depend on your body and your week, so if you want yours worked out properly, start with a Fueletics assessment. The Daily Fuelling Engine then adjusts training-day and rest-day intake as the plan changes.
Check the AQI tonight, know which scale your app uses, and decide where tomorrow's hard session happens before you set the alarm.
FAQs
Is it safe to run when the AQI is 200?
On the US scale, 200 is the top of "Unhealthy": healthy adults should cut back long or hard outdoor exertion and sensitive groups should stay in. Keep any outdoor run short and easy. On India's scale, 200 is the top of "Moderate," still air to move hard sessions away from.
Do masks help when running in pollution?
A well-fitted N95 filters fine particles but is hard to breathe through during hard efforts. Use one for the commute and warm-up.
Is indoor training better during smog season?
Usually, if the space is filtered and ventilated. A crowded, poorly ventilated room may not be.
Can diet protect your lungs from air pollution?
No diet or supplement has been shown to protect healthy athletes from particle pollution. Manage it with timing, location and indoor training.
Research References
Marr LC, Ely MR. Effect of air pollution on marathon running performance. Med Sci Sports Exerc. 2010;42(3):585–591. doi:10.1249/MSS.0b013e3181b84a85
Rundell KW. Effect of air pollution on athlete health and performance. Br J Sports Med. 2012;46(6):407–412. doi:10.1136/bjsports-2011-090823
Tainio M, et al. Can air pollution negate the health benefits of cycling and walking? Prev Med. 2016;87:233–236. doi:10.1016/j.ypmed.2016.02.002
Lichter A, Pestel N, Sommer E. Productivity effects of air pollution: evidence from professional soccer. Labour Econ. 2017;48:54–66. doi:10.1016/j.labeco.2017.06.002
Cusick M, Rowland ST, DeFelice N. Impact of air pollution on running performance. Sci Rep. 2023;13:1832. doi:10.1038/s41598-023-28802-x
Hung A, Koch S, Bougault V, et al. Personal strategies to mitigate the effects of air pollution exposure during sport and exercise: a narrative review and position statement by CASEM and CSEP. Br J Sports Med. 2023;57(4):193–202. doi:10.1136/bjsports-2022-106161
Whyand T, Hurst JR, Beckles M, Caplin ME. Pollution and respiratory disease: can diet or supplements help? A review. Respir Res. 2018;19:79. doi:10.1186/s12931-018-0785-0
US EPA. Revised Air Quality Index for PM2.5 (fact sheet), 2024. epa.gov
American Lung Association. Air Quality Index. lung.org
Central Pollution Control Board (India). National Air Quality Index: categories and breakpoints. summary via Indian Economic Service
