Is it safe to exercise outdoors today?

The bottom line

Outdoor exercise is healthy on most days. Three kinds of days make it a bad idea: high AQI, high heat plus humidity, and high UV. Knowing which is which keeps you out of A&E.

Air quality and exercise

When you train, you breathe ten to twenty times harder. Whatever's in the air, you inhale a lot more of it. This is why a run on a polluted day is genuinely worse for your lungs than just walking around in it.

• AQI 0 to 50: Train as normal.
• AQI 51 to 100: Fine for most. Asthmatics and kids should ease off.
• AQI 101 to 150: Move the session indoors or cut it short.
• AQI 151+: Don't. Treadmill, gym, or rest day.

Heat and humidity

Your body cools by sweating. Sweat needs to evaporate to cool you. When humidity is high, sweat just drips. Heat illness sneaks up fast.

Watch the "feels-like" temperature, not just air temperature. Over 30°C with humidity above 70% is dangerous for hard training. Over 35°C feels-like, skip it or train before 7am.

UV and outdoor sport

Long sessions on high-UV days leave you burnt. Hat, SPF 30+, UV-rated sunglasses, cover the shoulders. Avoid the 11-to-3 window if you can.

Pollen and outdoor running

If you have hay fever, pollen peaks twice a day: 5 to 10am and 7 to 9pm. Mid-afternoon is your window. In peak weeks, just go indoors.

Cold weather running

Below 4°C, breathing cold dry air can set off asthma or bronchial spasm in anyone prone. A buff or scarf over your mouth pre-warms the air. Below -10°C, properly cover your face or stay in.

Check before you head out

Open Window Today's "Outdoor exercise" card folds AQI, temperature, UV, and rain into one answer.

How air quality changes what exercise does to you

Exercise is good for you, but it changes how you breathe in a way that matters on polluted days. When you work out you breathe far more air, more deeply, and often through your mouth, which bypasses the filtering your nose normally does. That means a hard outdoor session on a high-pollution day delivers far more fine particulate matter deep into your lungs than the same air would at rest. The fitter and harder you push, the more you take in. This is why checking the air quality index before a run is not fussy; it genuinely changes the dose.

Reading the AQI for exercise decisions

As a rough guide, an air quality index under 50 is good and you can train freely. Between 50 and 100 is moderate, fine for most people but worth easing off if you have asthma or other lung conditions. Between 100 and 150, sensitive groups should cut intensity and duration or move indoors. Above 150 the air is unhealthy for everyone, and a hard outdoor workout is doing more harm than the exercise is doing good; take it inside. During bushfire smoke, when readings can spike far higher, outdoor exercise should simply wait.

Heat, humidity, and timing

Air quality is only one factor. Heat and humidity stack on top of it. Exercising in high heat forces your heart to work harder to cool you, and high humidity stops sweat evaporating, which is how cooling actually happens, so you overheat faster than the temperature alone suggests. On hot days, train in the cool early morning, carry water, and slow your pace. The morning also tends to have lower pollution and lower temperatures at once, which is why it is the safest window for outdoor exercise on a marginal day.

Frequently asked questions

Is it bad to exercise when air quality is poor?

Yes, when the index is high. Exercise multiplies how much air you breathe in, so a hard outdoor session on a polluted day delivers a much larger dose of pollutants. Above an index of 150, move your workout indoors.

Can I run during bushfire smoke?

It is best not to. Smoke readings can climb far into the hazardous range, and heavy breathing pulls that deep into your lungs. Wait for the smoke to clear or train indoors with windows shut.

What is the safest time of day to exercise outdoors?

Usually early morning, when temperatures and, often, pollution are both at their lowest. It is the most reliable window on a hot or marginal-air-quality day.

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