Be sure to check your local air quality just before heading out, Dr. Strickland says, since pollution levels change throughout the day.
The Advantages of Speed
Most of us might assume low-intensity activities would be preferable in smoke, since we wouldn’t be breathing as hard. But, “surprisingly, there is not yet any evidence that, for a given duration, higher-intensity exercise is more harmful than lower-intensity exercise,” says Dr. Michael Koehle, the director of the Environmental Physiology Laboratory at the University of British Columbia.
He was a co-author of a telling 2014 study in which 18 young male athletes pedaled stationary bicycles for 30 minutes on four separate visits. During two sessions, they rode gently while wearing masks that pumped in normal air on one ride, and diesel fumes on the other. During the remaining sessions, the cyclists pedaled strenuously, while again breathing normal air and then polluted air.
Throughout, the scientists checked parameters of lung function and, to their surprise, found that riders’ lungs seemed to labor more when they pedaled lightly in the polluted air than when they hammered.
A subsequent 2019 study using the same methods found that riders pedaling hard while breathing pollutants likewise did not develop more markers of incipient inflammation in their bloodstreams than they did while cruising.
Of course, diesel pollution is not wildfire smoke, and both studies focused on hardy male athletes. But the findings are suggestive, Dr. Koehle says. “If I had to choose between a short, 20- to 30-minute, more-intense bike ride or a longer, easier, three-hour ride, based on the science, I’d recommend the shorter, more-intense workout, just because it would lead to two-and-a-half hours less air-pollution exposure.”
Is there a time limit? “I’d say there is no clear time cutoff based on the science,” Dr. Koehle said. But if the air quality is orange or better, “something in the range of 30 to 60 minutes” spent exercising outside “seems reasonable.”