On a midsummer day in Miami, temperatures can exceed 32°C with high humidity. In a full stadium of 65,000 fans, it can be several degrees hotter, posing a potential health risk to players.

These are the conditions some teams will endure at the 2026 FIFA World Cup in June-July, the hottest months across much of North America.

FIFA has already acknowledged the risk, introducing cooling breaks in each half of all matches for the first time at a World Cup.

But is this enough to protect players in the heat?

It’s not just the high temperatures

When we talk about heat stress in sport, we are not just referring to air temperature.

What matters for the human body is a combination of heat, humidity, solar radiation and airflow – often summarised by the “wet-bulb globe temperature” index, originally developed in the 1950s to curtail heat illness during military training.

Soccer presents a particular challenge under high wet-bulb globe temperature conditions. Elite players routinely cover 10-13 kilometres per match, repeatedly sprinting, decelerating and changing direction.

This produces substantial internal metabolic heat, while opportunities for heat loss are limited by clothing, match structure, restricted access to shade, airflow or other cooling technologies.

If heat production exceeds heat loss, core temperature rises. This places more strain on the cardiovascular system, elevates perceived effort, impacts performance and increases the risk of exertional heat illness, which can include ailments such as muscle cramps and heat exhaustion. At the extreme end, exertional heat stroke, a life-threatening medical emergency can........

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