When to move training indoors during the haze, how to read the API bands, and how to keep strength and cardio on track through Malaysia's hazy weeks.
When the Air Pollutant Index (API) is above 100, move your exercise indoors. At 0 to 100 you can train outside as normal, and above 200 you should stay indoors and keep activity light. You do not need to stop training during the haze. You only need to change where you do it, and to have an indoor plan ready before the haze arrives.
Why exercising in haze is different from resting in it
When you exercise you breathe faster and more deeply than at rest, so you draw far more air into your lungs, and through your mouth, which bypasses some of the filtering of the nose. In haze that air carries fine particles. A hard outdoor session therefore raises your exposure to exactly the pollution you are trying to avoid. The harder the effort, the larger the extra dose.
This does not mean outdoor activity is always a bad trade. A modelling study of walking and cycling in cities worldwide (Tainio et al., 2016) found that the health benefits of regular activity outweighed the harm of air pollution in most settings, and that cycling only tipped into net harm in a small number of the most polluted cities. That research looks at long-term average pollution, not a severe haze episode, so it should not be read as permission to run hard on a day the API is 180. It does show that the answer to bad air is to change the setting, not to give up being active.
How to read the API bands
Malaysia’s Department of Environment (DOE) publishes the API hourly. It is built from six pollutants, including PM2.5 and PM10, and the reading you see is driven by whichever pollutant is worst at that station. Check your own area, since Klang, Shah Alam, Petaling Jaya and Putrajaya can differ on the same day.
| API | Category | What to do with training |
|---|---|---|
| 0 to 50 | Good | Train outdoors as normal |
| 51 to 100 | Moderate | Fine for most people; sensitive people stay alert for symptoms |
| 101 to 200 | Unhealthy | Move hard sessions indoors; high-risk groups limit outdoor activity |
| 201 to 300 | Very unhealthy | Stay indoors; older adults and high-risk groups reduce activity |
| 301 and above | Hazardous | Stay indoors and rest; seek medical advice if unwell |
These bands follow the DOE’s published categories. The training suggestions are our practical translation of the official health advice, which is to reduce strenuous outdoor exertion from 101 upwards.
Check before you go, not after
Look at the DOE’s APIMS site or the MyIPU app before you leave the house, and again if the sky looks hazy or you can smell smoke. Readings can change within a few hours, so a clear morning does not guarantee a clear evening.
Who should move indoors earlier
The groups Malaysian health advice treats as higher risk are children, older adults, pregnant women and people with asthma, COPD, other chronic lung disease or cardiovascular disease. If you are in one of these groups, treat an API in the upper moderate range as your cue to go indoors, not 101. Our guide to exercise with COPD and asthma covers action plans in more detail.
Stop at once and rest indoors if you notice:
- Cough, wheeze or a tight chest
- Unusual breathlessness for the effort
- Burning eyes or throat that does not settle
- Chest pain, palpitations or dizziness
Chest pain, fainting or severe breathlessness need urgent medical attention, not a rest and a sip of water. If you are unsure whether your heart or lungs are safe to train, read when to get medical clearance before exercise.
Your indoor plan B
A haze week costs you very little if the plan is already written. Keep these three options ready:
- Strength at home. Two full-body sessions a week is the baseline in the WHO 2020 guidelines (muscle-strengthening on 2 or more days). Squats, hip hinges, rows with a band and carries need a small corner and no extra equipment. See strength training at home in Malaysia.
- Indoor cardio. A treadmill, stationary bike or brisk loops in an air-conditioned mall keep your weekly aerobic minutes up. The WHO target for adults is 150 to 300 minutes of moderate activity a week. Our mall walking guide lists suitable venues, and how to find your Zone 2 shows how to pace it.
- Balance and mobility. Single-leg stands, heel-to-toe walking and gentle mobility work need no space and no equipment.
For ready-made sessions, see indoor exercise for hot and hazy days and the no-equipment longevity workout.
A simple haze-week template
| Day | Session |
|---|---|
| Mon | Home strength, 30 to 40 minutes |
| Tue | Indoor walk or bike, 30 to 45 minutes, easy pace |
| Wed | Balance and mobility, 15 to 20 minutes |
| Thu | Home strength, 30 to 40 minutes |
| Fri | Indoor cardio, 30 minutes |
| Weekend | Rest, or outdoor walk only if API is 100 or below |
Make the indoor air better too
Indoor air is not automatically clean in a haze. Keep windows and doors closed during the worst hours, run air-conditioning on recirculate if it has clean filters, and if you own an air purifier, run it in the room where you train. These steps lower exposure but will not remove it, so they support the decision to stay in rather than replace it.
Do not let a hazy spell break the habit
The real risk of the haze is not one missed run. It is a two-week gap that turns into a two-month gap. Treat the haze like a heavy rain week: swap the setting, keep the schedule, and return outdoors when the API settles below 100. Heat adds its own limits, so also see exercising in Malaysia’s heat and humidity.
Key takeaways
- Train outdoors when the API is 100 or below; move indoors from 101, and stay indoors above 200.
- Older adults, children, pregnant women and people with heart or lung conditions should switch indoors earlier.
- Masks do not make hard outdoor exercise in haze safe; changing the setting does.
- Keep an indoor plan B of home strength, indoor cardio and balance work so a hazy week costs you almost no progress.
- Stop and seek help for chest pain, severe breathlessness or fainting.
If you would like a programme that already has an indoor option built in, we run physiotherapist-led home-visit assessments across KL and Selangor. See our services.