Exercise and Training in the Haze, Singapore Edition. Lessons from the Australian Bushfires
Updated: 3 days ago
For athletes, training rarely stops simply because the weather becomes difficult. However, when bushfire smoke - or in Singapore haze - fills the air, continuing with intense outdoor exercise may carry health and performance risks that are easy to underestimate.
A position statement from the Australian Institute of Sport (AIS), endorsed by the Australasian College of Sport and Exercise Physicians and Sport Medicine Australia, explains why smoke exposure deserves careful consideration from athletes, coaches, medical teams and sporting organisations.
The statement, published in the Journal of Science and Medicine in Sport in 2023, reviews evidence on bushfire smoke, exercise and health. Its central message is straightforward: athletes should monitor fine-particle pollution, particularly PM2.5, and adjust training duration, intensity and location when air quality deteriorates.
As ever, please talk to your doctor or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle, especially if you are under treatment. Links to all studies at bottom of page.
Why bushfire smoke is a concern
Bushfire smoke is a complex mixture of gases and particles produced when vegetation burns. It can contain carbon monoxide, nitrogen oxides, hydrocarbons, volatile organic compounds, trace minerals and particulate matter.
Particulate matter is commonly classified according to particle size. PM10 refers to particles measuring 10 micrometres or less in diameter, while PM2.5 describes finer particles measuring 2.5 micrometres or less.
PM2.5 is particularly important because these particles can travel deep into the respiratory system. They may also carry other pollutants, increasing the potential for irritation and inflammation. The AIS position statement notes that PM2.5 is likely to be a more useful indicator of health risk than broader measures of air pollution, although PM10 can also provide valuable information.
The composition of smoke may vary according to the vegetation burned, the temperature of combustion and environmental conditions. The statement also emphasises that it remains unclear how the toxicity of bushfire smoke compares directly with pollution from traffic or industrial sources.
Exercise changes the dose entering the lungs
One of the most important points in the statement is that exercise does not merely take place in polluted air, it can substantially increase the amount of polluted air inhaled.
During exercise, breathing becomes faster and deeper. Three changes are particularly relevant:
Tidal volume increases, meaning more air is inhaled with each breath.
Breathing tends to shift from the nose towards the mouth, reducing the filtering effect of the nasal passages.
Overall minute ventilation increases, so a much greater volume of air passes through the respiratory system.
The AIS review cites research suggesting that a sixfold increase in ventilation during high-intensity exercise may increase particle deposition in the lungs by approximately tenfold. It also discusses modelling indicating that one hour of high-intensity exercise could produce a similar amount of particle deposition to around ten hours of exposure at rest.
These comparisons should not be interpreted as a precise prediction for every athlete. Individual responses vary considerably. Nevertheless, they illustrate why a short, demanding training session can create a much greater inhaled dose than simply spending the same amount of time outdoors walking or resting.
Symptoms may begin before performance visibly declines
Bushfire smoke can irritate the upper and lower airways. Possible symptoms include coughing, throat or nose irritation, eye discomfort, wheezing, chest tightness and breathlessness.
The effects are not necessarily limited to the respiratory system. The paper discusses possible changes involving oxidative stress, inflammation, blood clotting processes and the autonomic nervous system. However, research involving athletes remains limited, and many of these effects are subtle or difficult to detect outside a laboratory.
This is important for high-performance sport because a small physiological disturbance may occur before an athlete notices obvious symptoms. An athlete might experience unusual breathing effort, reduced tolerance of a familiar training pace, slower recovery or a mismatch between expected workload and actual performance.
The statement does not establish a definitive PM2.5 level at which performance always declines. Instead, it advises coaches and athletes to recognise that small changes may precede more obvious health problems.
Asthma and airway sensitivity require particular care
Not every athlete responds to smoke in the same way. People with asthma or a history of increased airway responsiveness may be more vulnerable to bronchoconstriction and other smoke-related symptoms. The statement notes that asthma is relatively common among elite athletes, particularly in endurance and aquatic sports. Some athletes without a formal asthma diagnosis may also have increased airway responsiveness or other forms of airway dysfunction.
A further concern is exercise-induced laryngeal obstruction, which can affect breathing during strenuous activity. The authors suggest that irritation of the upper airways from smoke may be a possible contributing stimulus, although the precise relationship requires further research.
Importantly, an athlete’s previous experience is not a perfect safeguard. Someone who has tolerated smoke in the past may still develop symptoms under different conditions, especially after several days of exposure, following a respiratory infection or during unusually intense exercise.
The AIS therefore recommends that athletes with asthma maintain an up-to-date asthma management plan and discuss smoke-affected exercise with their doctor. Prescribed medication and relevant action plans should be accessible during training and competition.
Air quality can affect health after the smoke has cleared
A common mistake is to assume that once visibility improves, the risk has disappeared. The position statement explains that air-quality measurements can change rapidly and that pollution levels may vary substantially over relatively short distances.
It also highlights evidence that emergency-department presentations and asthma-related problems can occur several days after elevated smoke exposure. For susceptible people, the effects may persist for approximately three to five days, although the precise recovery period is uncertain.
This has practical implications for training schedules. A team may experience poor air quality on Monday, see clearer skies on Tuesday and then plan a demanding outdoor session on Wednesday. However, recent exposure may still be relevant, particularly for athletes with asthma, recent respiratory illness or a history of smoke sensitivity.
The authors acknowledge that there is insufficient evidence concerning repeated exposures before full recovery. As a result, consecutive days of outdoor training in smoke should be approached cautiously.
What do the recommended PM2.5 categories mean?
The AIS position statement presents broad exercise guidance based on PM2.5 concentrations. These are not absolute safety thresholds, and individual responses may differ. Note, these Australian standards differ from those in, say, Singapore - see further below.
Below 25 micrograms per cubic metre
This range is generally considered suitable for normal exercise for most people. Even here, athletes should remain alert to symptoms, particularly if they are sensitive to smoke or have recently experienced respiratory illness.
25–50 micrograms per cubic metre
This is a cautionary range, especially for people who are sensitive to air pollution. Most individuals may tolerate normal activity, but prolonged, high-intensity endurance exercise may need to be moved indoors or modified.
51–150 micrograms per cubic metre
The statement categorises this as poor conditions for exercise. Athletes who are sensitive to pollution should limit exposure as much as practical. Prolonged, high-intensity endurance sessions, such as long-distance running, cycling or rowing, are preferably completed in a cleaner indoor environment.
Shorter intermittent activities, such as some forms of tennis, cricket or skills training, may create less exposure than continuous endurance exercise. However, they are not risk-free, and athletes may still develop symptoms unexpectedly.
Above 150 micrograms per cubic metre
The authors consider these conditions likely to be hazardous for outdoor exercise. Sporting organisations should make every effort to reduce exposure by postponing events, relocating activities indoors or shortening time outdoors. Decisions about organised high-level sport should involve medical staff, coaches and officials.
The paper stresses that these categories are based partly on expert judgement because research has not established definitive thresholds for every athlete, sport or environmental condition.
Singapore
Visibility is a warning sign, not a measurement
Smoke often produces a noticeable reduction in visibility. This can be a useful warning that conditions are worsening, particularly when official readings are unavailable or delayed.
However, visibility is influenced by humidity, weather and the chemical composition of particles. It should therefore not be treated as a precise substitute for PM2.5 monitoring.
The AIS recommends using current government air-quality data wherever possible. Sporting clubs may also consider appropriately designed outdoor PM2.5 monitors, although cost and accuracy can be limiting factors. Readings from indoor monitors may not accurately represent conditions on a playing field or running track.
Because official monitoring stations may be some distance away, athletes and teams should recognise that local conditions can differ from published readings.
Practical steps for athletes and coaches
A sensible approach to smoke-affected training includes:
Check PM2.5 before training. Do not rely solely on how the sky looks or how far can be seen.
Consider the previous several days. Recent exposure may remain relevant even when current readings improve.
Reduce intensity and duration when necessary. High-intensity endurance sessions create particularly large increases in inhaled air.
Move training indoors when conditions are poor. Choose a facility with better air quality rather than assuming that any indoor location is automatically suitable.
Know individual risk factors. Asthma, airway sensitivity and recent respiratory infection may increase vulnerability.
Watch for changes in normal performance. Unexpected breathlessness, coughing, chest tightness or an unusual training response should not be ignored.
Seek medical advice early. Athletes with persistent or worsening symptoms should consult a medical professional rather than attempting to train through them.
Final Thoughts
Bushfire smoke - haze - creates a difficult balancing act for high-performance sport. Athletes need consistent training, but intense exercise in polluted air can greatly increase the amount of smoke reaching the lungs. The risks are especially important for people with asthma or increased airway responsiveness, although even athletes without known respiratory conditions may experience symptoms.
The AIS position statement does not suggest that all exercise must stop whenever smoke is present. Instead, it promotes informed decision-making based on PM2.5 levels, training intensity, exposure duration, recent air quality and individual susceptibility. Monitoring conditions, modifying sessions and prioritising recovery can help you to protect your health without abandoning physical activity altogether.
Stay Healthy,
Alastair
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Related Studies and Resources
Mooney M, Panagodage Perera NK, Saw R, Waddington G, Cross TJ, Hughes D. Exercise in bushfire smoke for high performance athletes: A Position Statement from the Australian Institute of SportEndorsed by Australasian College of Sport and Exercise Physicians (ACSEP) and Sport Medicine Australia (SMA). J Sci Med Sport. 2023 Feb;26(2):98-108. doi: 10.1016/j.jsams.2023.01.004. Epub 2023 Jan 13. PMID: 36858652.
IQAir Singapore Note: these numbers also can differ from the Singapore standard. See NEA's post here.
Other
Hasnain MG, Garcia-Esperon C, Tomari YK, Walker R, Saluja T, Rahman MM, Boyle A, Levi CR, Naidu R, Filippelli G, Spratt NJ. Bushfire-smoke trigger hospital admissions with cerebrovascular diseases: Evidence from 2019-20 bushfire in Australia. Eur Stroke J. 2024 Jun;9(2):468-476. doi: 10.1177/23969873231223307. Epub 2024 Jan 23. PMID: 38258746; PMCID: PMC11318436.
Giles LV, Thomson CJ, Lesser I, Brandenburg JP. Running Through the Haze: How Wildfire Smoke Affects Physical Activity and Mental Well-Being. J Phys Act Health. 2024 Nov 6;21(12):1435-1445. doi: 10.1123/jpah.2024-0305. PMID: 39504954.
Ho AFW, Hu Z, Woo TZC, Tan KBK, Lim JH, Woo M, Liu N, Morgan GG, Ong MEH, Aik J. Ambient Air Quality and Emergency Hospital Admissions in Singapore: A Time-Series Analysis. Int J Environ Res Public Health. 2022 Oct 16;19(20):13336. doi: 10.3390/ijerph192013336. PMID: 36293917; PMCID: PMC9603816.
Hahad O, Kuntic M, Frenis K, Chowdhury S, Lelieveld J, Lieb K, Daiber A, Münzel T. Physical Activity in Polluted Air-Net Benefit or Harm to Cardiovascular Health? A Comprehensive Review. Antioxidants (Basel). 2021 Nov 8;10(11):1787. doi: 10.3390/antiox10111787. PMID: 34829658; PMCID: PMC8614825.
Cheong KH, Ngiam NJ, Morgan GG, Pek PP, Tan BY, Lai JW, Koh JM, Ong MEH, Ho AFW. Acute Health Impacts of the Southeast Asian Transboundary Haze Problem-A Review. Int J Environ Res Public Health. 2019 Sep 6;16(18):3286. doi: 10.3390/ijerph16183286. PMID: 31500215; PMCID: PMC6765769.
Ho AFW, Zheng H, Earnest A, Cheong KH, Pek PP, Seok JY, Liu N, Kwan YH, Tan JWC, Wong TH, Hausenloy DJ, Foo LL, Tan BYQ, Ong MEH. Time-Stratified Case Crossover Study of the Association of Outdoor Ambient Air Pollution With the Risk of Acute Myocardial Infarction in the Context of Seasonal Exposure to the Southeast Asian Haze Problem. J Am Heart Assoc. 2019 Mar 19;8(6):e011272. doi: 10.1161/JAHA.118.011272. PMID: 31112443; PMCID: PMC6475051.
Yap J, Ng Y, Yeo KK, Sahlén A, Lam CSP, Lee V, Ma S. Particulate air pollution on cardiovascular mortality in the tropics: impact on the elderly. Environ Health. 2019 Apr 18;18(1):34. doi: 10.1186/s12940-019-0476-4. PMID: 30999903; PMCID: PMC6471752.
Schulz AJ, Mentz GB, Sampson NR, Dvonch JT, Reyes AG, Izumi B. Effects of particulate matter and antioxidant dietary intake on blood pressure. Am J Public Health. 2015 Jun;105(6):1254-61. doi: 10.2105/AJPH.2014.302176. Epub 2014 Oct 16. PMID: 25320896; PMCID: PMC4400223.
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