Pollution can outweigh benefits of exercise
In some of the world's most polluted cities, exercising outside can actually do more harm than good.
It might sound like common sense that cycling to work is a healthier option than driving, but in some cities there is so much air pollution that the benefits of exercise are negated within minutes.
According to a recent study, fifteen major cities around the world have reached the point where the benefits of cycling are outweighed by the effects of air pollution within a mere half an hour.
Allahabad in India and Zabol in Iran are two such cities, while Riyadh in Saudi Arabia is slightly better with a 45-minute limit. In Delhi and Xingtai this figure increases to around one hour.
The polluted air itself is particularly nasty, with evidence suggesting that it can lead to everything from infections and heart disease to various types of cancer.
The researchers however were keen to emphasize that the benefits of exercise were only outweighed by high pollution levels in the most extreme of cases and that this should not discourage people outside of these areas from cycling to work or engaging in other physical activities.
"The benefits of active travel outweighed the harm from air pollution in all but the most extreme air pollution concentrations," said air pollution management lecturer Audrey de Nazelle.
"It is not currently an issue for healthy adults in Europe in general.