How the heatwave has affected players at the Club World Cup and what the lessons are for the 2026 World Cup

New York Times

10 hours ago

The heatwave that swept the United States in recent days caused concerns for players and fans at the Club World Cup. To try to manage the intense heat, players have covered themselves in ice-cold towels or placed their hands and feet in buckets of the stuff. Such was the heat in Charlotte on Tuesday that Harry Kane even dipped his head in.
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At Cincinnati's TQL Stadium, Borussia Dortmund's substitutes watched the first half of their game against Mamelodi Sundowns from the locker room rather than the bench to avoid the pitch-side heat. Dortmund coach Niko Kovac said he was 'sweating like I've just come out of a sauna' after his side won that game in 32C (89.6F) conditions.
After their game against Paris Saint-Germain in Pasadena, just outside Los Angeles, Atletico Madrid midfielder Marcos Llorente described the weather as 'impossible. Terribly hot. My toenails were hurting'.
In Philadelphia, Chelsea played in temperatures of around 36C (97F), which forecasters said felt more like 41C (106F). 'It is almost impossible to train or to make a session because of the weather,' Chelsea coach Enzo Maresca told reporters on Monday. 'This morning's session has been very, very, very short.'
But what exactly does heat do to an athlete's body? And how much of a problem can it really be?
Here The Athletic answers those questions and what it means for the rest of the Club World Cup — and the World Cup, which will be staged mostly by the U.S, again in June and July, with games also in the neighbouring countries of Canada and Mexico.
Any physical exertion in hot conditions will cause the body's temperature to rise. 'We sit about 37C (98.6F) at resting,' says Dr Chris Tyler, an environmental physiologist from London's University of Roehampton and an expert on heat stress in elite sports. 'Most people get into trouble if they are two to three degrees warmer than that, so we don't have much of a buffer.
'It's actually quite difficult to get the body that hot, but one of the ways to do it is to move quite quickly in hot conditions.'
The most obvious consequence of that rise in temperature is an elevation in your heart rate. This happens, explains Tyler, because the body sends more blood to the skin to try to get rid of some of the excess heat (the reason why some people get very red-faced when they're too warm).
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That leaves less blood in the core trunk of the body, and crucially, less blood in the heart, meaning it has to work harder to provide blood to the working muscles. That's why doing the same exercise at the same intensity is going to be harder — and feel harder — in higher temperatures than cooler ones.
The most obvious visual impact among professional footballers is their sweat response. They will start to perspire earlier and more rapidly as their body tries to cool itself down.
According to Geoff Scott, former head of medicine and sports science at Tottenham Hotspur, players lose a minimum of two litres (approaching four UK pints, over four in U.S. pints) of fluid per game playing in cooler temperatures in the Premier League. 'When it gets really hot and humid, that can go up to about five litres of fluid over the course of one game,' he tells The Athletic.
It's not just water they are losing through sweat either, it's electrolytes, too, and the depletion of essential ones such as sodium, chloride and potassium is a key concern. To combat that, Scott says that in the days before and especially on the day of a game, hydration is pushed at all opportunities to make sure players are drinking water and also sports drinks with adequate electrolytes.
'It's common now that teams will do sweat analysis on the players so they know which players sweat more and which ones lose more electrolytes in their sweat, and they can be targeted with specific drinks to make sure their electrolyte imbalances are addressed,' he says.
A player who gets into the 'dehydration zone' could suffer light-headedness, dizziness, fatigue and muscle cramps, but Scott says that, well before getting to that opint, there will be changes in their performance levels: 'You tend to start seeing them reduce their high-intensity running, and very elevated temperatures tend to affect their technical skills too, so the quality can drop off. They start to fatigue faster, too.'
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While an increase in sweating can cause issues regarding dehydration, it's also a good thing, because if it can evaporate from the skin, the perspiration will take some of the heat away with it. But, Tyler explains, in conditions where humidity is also high, a lot of that sweat won't be able to evaporate because there is already lots of moisture in the surrounding air.
'So players will be losing sweat,' he says, 'but it will be dripping off them rather than evaporating, which will be dehydrating without taking any heat away.'
If the rise in body temperature isn't controlled, it can lead to heatstroke.
'As the blood is all shunted to the skin, there's less volume of blood in your cardiovascular system,' explains Scott. 'And that's the problem – your blood pressure drops. Someone out for a casual jog who is getting close to that would probably stop, but these guys can't stop (during a match), so they're at more risk.'
To cope with soaring temperatures, athletes adapt the way they perform. In football, the average distance covered is reduced during hot-weather games and the action becomes more possession-heavy, explains Tyler.
'The good teams will adapt tactically. You see it in tennis as well, where good players will make the other players run a lot more. It's the same here; if you're Manchester City, you can play a very slow, possession-based game and let everyone else chase you for 90 minutes.'
There is physiological adaptation, too, with the body making subtle changes to be more efficient in the heat. One of those is an expansion of the plasma volume of a person's blood, meaning you end up with a greater volume of blood in the body than you had before.
'Now you have more blood, so you can send some to the skin and maintain blood flow to the working muscles without needing the heart to pump faster,' says Tyler. 'That means the heart rate won't go so high.'
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As well as sweating earlier, what comes out of the players' pores will also be different to normal, says Tyler, becoming more diluted, thus preserving essential electrolytes such as sodium chloride and potassium, which are lost through sweat.
Those adaptations in blood volume and sweat composition can help decrease the strain the players are under. The only catch is that those processes take time.
'How long they take is hard to say exactly,' says Tyler, 'but it seems like players would need at least five to seven days to see meaningful adaptations. But even after two weeks, they are still making adaptations to that stress.'
Given the short turnaround time between the end of the European season, late May for a lot of leagues, and the start of the Club World Cup on June 14, many of the teams involved won't have had much time to acclimatise before travelling to the United States.
Also of relevance is the fact a lot of the teams taking part in this tournament come from countries with typically cooler climates than their rivals from South and Central America, North Africa, and the Middle East, which makes the challenge even greater.
Tyler, whose research focuses on human responses to extreme hot and cold environments, and specifically on how to minimise the performance impairments observed in such conditions, says that for an event such as the Club World Cup, athletes would ideally want at least two weeks of 'heat adaptation training' before leaving for the host nation.
This usually involves heat tents or heat chambers, which mimic the conditions players will face on arrival. Heat lamps can also be used inside these to recreate the feeling of the sun's rays. Temperatures in the tents can range from 35-50C (95-122F) and the humidity rises from around 30 per cent to 80 per cent by the end of a session.
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It's an approach England's new head coach, Thomas Tuchel, used at their training camp in the recent June international window.
With the side's likely participation in next summer's World Cup in mind, players were asked to go through fitness tests inside heated tents, allowing performance staff to analyse how each of them responds to those conditions, including analysing their sweat rate and sweat composition.
'The idea,' says Tyler, 'is to do their normal training (or as close to it as possible) while getting their body hot in a controlled, safe environment.' Over time, he explains, players doing this start to adapt physiologically to perform better in higher temperatures. Once they arrive in the hot climate itself, they can continue to adapt.
Manchester City used their early training sessions in the States to try to speed up the adaptation, with manager Pep Guardiola holding long midday training sessions in the searing Florida heat at their base in Boca Raton, near Miami.
Juventus have been scheduling training to match the kick-offs of their group matches, with their English defender Lloyd Kelly telling the media they had trained 'the past 10 days in the hottest times of the day'.
'Being aerobically fit is advantageous anyway,' says Tyler, 'so if you're an elite player, you probably have some more tolerance for the heat than if you were a non-athlete.
'That could put teams like Auckland City (the part-timers from New Zealand) at an even bigger disadvantage, because they're not professional athletes, so their players are less fit than some other teams.'
World football governing body and Club World Cup organiser FIFA's policy on managing the temperature for players during games is to implement cooling breaks when the wet-bulb globe temperature (WBGT; an overall thermal-strain measure achieved by combining temperature, humidity, wind speed and solar radiation) exceeds 32C (89.6F) on the pitch.
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FIFA also said its medical experts 'have been in regular contact with the clubs to address heat management and acclimatisation', and that it was working with local medical authorities regarding heat management.
From the players' point of view, the Club World Cup represents a dry run for the national-team version in a year — a taste of what they might expect if they are among those taking part in football's biggest competition.
The challenge has been made clear at the Club World Cup: the toughest opponent might not be the team you're facing, but the heat.
The preparation for that has to start now.