At what AQI should you move a workout indoors?

Deciding when to take a workout inside comes down to two things: how high the AQI (air quality index) is, and how hard you mean to go. No agency sets an exact number for moving exercise indoors. The harder and longer you work out in dirty air, the more of it you pull into your lungs¹, so past a point the sensible move is to head in.

For a healthy adult, that line sits higher than you'd expect. At 151 to 200, the Unhealthy band, everyone active outdoors may start to feel it.¹ Here the advice is to reduce long or hard efforts and take more breaks, not to head inside yet.²³ Once the air turns Very Unhealthy, 201 to 300, avoid those efforts and move them indoors²³, where health effects are expected across the whole population.¹ At 301 and above, all outdoor activity should stop.²³

The line comes earlier if poor air hits you harder. People with heart or lung disease, older adults, and children feel it sooner and should ease off from the orange band, 101 to 150.¹³ For them, 151 is the point to avoid long or intense outdoor efforts and move them indoors.²³

Ultimately it comes down to listening to your body. As the air quality worsens, reduce the length and intensity of your exercise and consider moving indoors.² And if you have significant shortness of breath, any chest pain or tightening, or feel dizzy or light headed then that's a signal to stop and get somewhere with cool, clean air.