What Happens to a Footballer’s Body When Football Is Played at 110 Degrees?

The heat has arrived.

The first two weeks of World Cup 2026 were relatively mild, but a heatwave has now gripped large swathes of the United States and temperatures have soared to dangerous levels. Weather experts have confirmed that an Extreme Heat Warning is in effect for Philadelphia until 8pm Saturday — the same city where France face Paraguay at 5pm.

The forecasted high temperature in Philadelphia is 100°F (38°C), close to the city’s all-time record of 103°F (39°C) set on 4 July 1966. The Heat Index — which accounts for humidity — is expected to reach between 105°F (41°C) and 115°F (46°C). Severe thunderstorms with damaging winds are also possible after 5pm.

On the pitch itself, the situation is even more extreme. Field temperatures could exceed 110°F (43°C). FIFA banned artificial turf for 2026 and invested significantly in natural grass surfaces at all 16 stadiums — a decision that provides some relief, since natural grass runs meaningfully cooler than artificial alternatives. But 110-120°F (43-49°C) on the grass surface remains brutal for players’ feet and lower legs, and the radiant heat rising from the ground adds to the thermal stress already imposed by air temperatures of 100°F.

Researchers warned before the tournament that temperatures at 14 of the 16 stadiums across the United States, Mexico and Canada could exceed dangerous thresholds. In an open letter to FIFA, health experts warned of “worrying levels of heat stress” on players and called for longer cooling breaks, clearer postponement protocols and stronger protections for those competing.

But what does extreme heat actually do to a footballer’s body?

To answer that, three leading experts provided their analysis: Chris Harris, sports scientist at Precision Fuel & Hydration; Dominic Rae, head of sports medicine at Ten Percent Club with Premier League and UAE experience; and Jamie Mitchell, performance scientist at 292 Performance.

The Measurement System That Matters

The key metric for assessing heat risk during outdoor sport is wet bulb globe temperature (WBGT) — a measure developed initially by the US Navy and Marine Corps that estimates the combined effects of air temperature, humidity, wind speed and sunlight on the human body.

WBGT Safety Thresholds

FIFA’s emergency care manual states that suspension or postponement is only formally considered when WBGT is “near, at or above 32°C (89.6°F)”. Global player union FIFPro recommends that threshold should be 28°C. The open letter to FIFA described the 32°C threshold as “impossible to justify.”

The dispute over those four degrees of difference is not academic. It is the difference between players competing in conditions that international sporting medicine considers dangerously stressful and playing in conditions where a delay would be considered necessary by the bodies representing the players themselves.

What Happens Inside the Body

1. The Core Temperature Rise

“The human body is essentially an engine when it comes to sports performance,” says Harris. “As we move or exercise, we generate heat, quickly increasing our core temperatures.”

Elite footballers expend enormous amounts of energy and generate substantial heat in normal conditions. In Philadelphia’s forecasted conditions, the problem compounds rapidly.

“If you then put that human being into a particularly hot environment and ask it to do exactly the same thing, you’re receiving heat from outside of your body into you,” Harris explains. “That becomes problematic when the temperature is similar to or above your core temperature, which wants to be around 37°C (98.6°F). You’re speeding up the rate at which you’re filling your heat tolerance tank.”

The rise in core temperature is, in Harris’s words, “the danger factor.”

Core Temperature Danger Thresholds

“We have a pretty narrow window within which we can tolerate changes in core body temperature,” Harris adds. “When you get cold, you start shivering to generate muscle heat. When you’re too hot, you start sweating. The danger comes when you continue to generate heat and push through your ability to cool down.”

2. Blood Vessel Dilation and the Sweating Mechanism

The body’s first response to excessive heat is to redirect blood flow toward the skin, allowing heat to dissipate.

“The reason people tend to go red is that your blood vessels are vasodilating — expanding — to get blood to go close to the skin surface,” Harris explains. “If the environment around you is cooler than you are, some of that heat will be dissipated.”

The next line of defence is sweating — but it is not the sweat itself that cools the body. It is the evaporation of sweat.

“If you’ve ever done exercise and then turned a fan on or walked out of a hot building into a cold space and suddenly felt chilly, it’s because your sweat isn’t doing much when the environment is hot, but it is doing a lot when it’s cold around you, because then it starts to evaporate and you dispel that energy — which is heat — into the environment.”

This explains why Philadelphia’s humidity intensifies the danger. Above 50% humidity, the effectiveness of sweating drops sharply because moisture in the air prevents evaporation. The sweat remains on the skin rather than cooling it.

This is also why England based their pre-World Cup training camp in Miami — deliberately acclimatising to conditions similar to those they would encounter during the tournament. Acclimatisation trains the body to sweat earlier and more efficiently under thermal stress.

3. Hydration: Fluid Loss and the Electrolyte Problem

Sweating creates two distinct physiological problems: fluid loss and electrolyte depletion. Both matter. Both are individually dangerous. Together, they compound.

Electrolytes — particularly sodium and chloride — enable muscle contraction and nerve signalling. They are lost through sweat at rates that vary significantly between individuals.

“A heavy salt sweater will lose over a gram of sodium per litre of sweat,” says Rae. “That’s a lot. In a game we will see some players lose three to five kilograms in fluid, so someone could be losing five grams of salt plus the other electrolytes that go with that.”

Fluid and Electrolyte Loss During High-Heat Match

“Electrolytes are involved in the relationship between brain and muscle,” says Rae. “If we’re losing that much electrolyte during a game, think what is happening from a physical output point of view and the ability to rapidly fire muscle and contract tissue. These are important to perform but also to reduce injury.”

Elite teams will have conducted individual sweat tests on every player — analysing the specific composition of each player’s sweat to design personalised hydration strategies. In cooling breaks, the priority is not volume of fluid but electrolyte concentration.

“You can’t replenish enough liquids in a three-minute break,” Rae explains. “We make 200ml bottles of water and concentrate them with high-dose electrolytes.“

4. Gastrointestinal Distress

During intense exercise in heat, the body prioritises blood flow to the skin, working muscles, heart and lungs. The gut — not considered a vital organ during exercise — receives a reduced supply.

“This can lead to an increased risk of gastrointestinal issues during exercise in the heat,” says Harris. “We see this a lot in the endurance space where people struggle with stomach issues.”

While athletes often describe feeling unable to tolerate certain foods or drinks during heat exertion, Harris says the root cause is typically hydration-related. When blood plasma volume drops through sweat loss without adequate replacement, the body cannot maintain normal gut function.

5. Dizziness and Fainting

The same blood volume mechanism that affects gut function also explains why players feel dizzy or faint in extreme heat.

“Imagine you’ve got a set quantity of blood that fills a certain space in your body,” Harris explains. “As you remove fluid from that blood through sweating, blood plasma volume decreases. If you then put additional stress onto that body, you reduce the likelihood that the vasculature fills instantly.”

When a player bends down and stands up quickly — as happens constantly in a football match — gravity works against the blood pressure needed to supply the brain. The result is the disorienting “head rush” that can lead to stumbling, loss of balance or, in extreme cases, collapse.

“Usually, this is down to dehydration compromising your blood volume, which affects blood pressure regulation throughout your body,” Harris says.

6. Glycogen Depletion and the Loss of High-Intensity Output

The body’s preferred energy source during exercise is carbohydrate, stored as glycogen in the muscles. In extreme heat, glycogen stores deplete significantly faster than in normal conditions.

“That muscle glycogen is essential to high-intensity performance,” says Mitchell. “So in the heat, as those levels get depleted faster, those high-intensity bursts — often the things that change a football game — become harder.”

What Glycogen Depletion Means for a Footballer

Rae recommends using cooling breaks specifically to introduce energy gels alongside electrolytes. “You can use a sugar-based drink, but gels are probably the better solution because if you are going to utilise stomach space, you want that to be with as much fluid as someone can take.”

7. Cognitive Decline

The effects of extreme heat are not limited to the body. The brain suffers too.

“The brain is a central governor when it comes to fatigue in exercise,” Mitchell explains. “When it’s hot, cognitive functions — such as decision-making — can become more difficult. People aren’t used to operating with such a high thermal strain. It’s a double whammy — you’re more physically tired, so your decision-making and coordination might be decreased, but then you’re also more mentally tired because your brain is working on overdrive.”

The decision errors that occur late in tight matches — mistimed tackles, poor passes, defensive positioning failures — are not simply matters of concentration. They are physiological. The brain under thermal stress does not function with the same clarity as it does in normal conditions.

Mitchell adds that external tools can partially trick the brain into tolerating higher heat loads. An ice towel applied to the back of the neck, for example, can lower the brain’s perception of thermal stress even when core temperature remains elevated — providing a small but meaningful cognitive benefit during cooling breaks.

8. System Shutdown: Heat Illness and Its Long-Term Consequences

When the body can no longer manage the accumulation of heat through sweating, dilation and blood flow adjustment, more dramatic processes begin.

“Heat illness is characterised by symptoms when heat stresses your body so much it begins to shut down certain processes,” Harris explains. “First, it wants you to stop exercising. You might start suffering from muscle cramps. Your digestive system is going to shut down. There might be incredible thirst.”

One of the most counterintuitive symptoms of severe heat stress is shivering — the body beginning to lose its ability to regulate its own temperature correctly.

“In cases of severe dehydration, the body can stop sweating to conserve fluids, because that is a primary mechanism it needs to hold on to,” says Harris. “That’s often what suddenly skyrockets the core temperature, because all of a sudden, you’ve switched off the major mechanism cooling you down.”

The long-term implications deserve serious consideration, particularly in a tournament context where players must recover and compete again within days.

“Your brain learns that last time it got to these core temperatures it was in real danger,” Harris explains. “So you end up lowering the threshold of when those things start to creep in and actually become more predisposed to having heat issues than you did before. So you want to avoid those things at all costs — because it doesn’t only impact your health and performance now, but it will have future implications as well.”

The Stakes for France vs Paraguay

France are the tournament favourites. Paraguay eliminated Germany in one of the biggest upsets in World Cup history. The match has legitimate sporting stakes for both sides regardless of conditions.

But those conditions now add a dimension that has nothing to do with tactics or individual quality. Both squads will have implemented heat preparation strategies. Both sets of medical staff will be working throughout the match to manage fluid and electrolyte replacement. Both benches will be monitoring players for the physiological warning signs that heat stress produces.

The hydration breaks that have been discussed primarily as a tactical tool throughout this World Cup will be, in Philadelphia on Saturday, something more fundamental. They are medical necessities.

Whether the conditions ultimately prove decisive — whether a player cramps in the 85th minute, whether a goalkeeper’s reactions slow in extra time, whether a defender misjudges a header through cognitive fatigue — may depend less on preparation than on individual physiology.

In 100°F heat with a field temperature that could exceed 110°F, every player on that pitch will be operating at the outer limits of what the human body can safely sustain.

Related Article: Why France Look Like the Team to Beat at the 2026 World Cup
Continue Reading: World Cup 2026: How Deschamps’ Tactical Tweaks Are Getting the Best Out of Mbappé and France

Read More: From Giant-Killers to Genuine Contenders: Morocco’s New Generation Is Taking Them Further
Also Read: Morocco’s Yassine Bounou, The Canadian-Born Goalkeeper Standing Between Canada and History

FAQs