Evidence on healthy adult populations in high-income countries advocates for regular physical activity, even if the air quality does not meet the levels recommended by WHO, as it provides health benefits. However, scientific evidence is weak for all the examined associations in low and middle- income countries (LMIC), for indoor settings (e.g. households, dedicated places for physical activity practice), and for susceptible subpopulations (children, old, people with pre-existing conditions). Specifically, evidence on short-term impacts suggest that air pollution diminishes (but not eliminate) the beneficial effects of physical activity, in populations with diseases such as cardiovascular and respiratory conditions and for those who are healthy. In the long-term, studies suggest that air pollution slightly reduces the protective effect of physical activity on mortality. Also, modelling studies have estimated that in most situations, the benefits of physical activity should be larger than risks of air pollution, at least in walking and cycling environments.