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.

Related reads