As haze blankets parts of the country, outdoor runners face hidden cardiovascular risks. Experts weigh in on how fine particulate matter affects endurance training and when it is time to pause.

For many Malaysians, running is more than exercise. It is a way to manage stress, maintain fitness and prepare for the next 10-kilometre race, half marathon or full marathon. Early mornings often find recreational runners gathering in parks, on city roads and around neighbourhoods to complete their training miles. But when the sky turns grey and haze blankets the surroundings, an important question arises: is the air we breathe while running doing more harm than we realise?

While the cardiovascular benefits of regular physical activity are well established, exercising in polluted air presents a different challenge. During running, breathing becomes faster and deeper, increasing the amount of air—and potentially harmful pollutants—inhaled. The concern is not limited to the lungs. Fine airborne particles and other pollutants can also affect blood vessels, blood pressure and the body’s inflammatory response.