Here the case study becomes most instructive, because the tournament is testing the preparation directly, in front of us, and what we are seeing aligns closely with what the physiologists predicted. We are now in the quarter-finals, in the hottest weeks of the summer, and this is where both the football and the conditions reach their most intense. 

The heat is visibly shaping play. Brazil forward Vinícius Júnior described its tactical effect plainly after an early draw with Morocco: “In the second half, with the heat, the pitch dries out very quickly. The game becomes very sluggish, and we can’t get into our rhythm”. This is precisely the mechanism the science predicts: as core temperature rises and the body prioritises cooling, high-intensity output falls and the game slows. 

And as the knockout rounds have progressed, the conditions have not eased: they have escalated. A heat dome settling over the eastern United States and Canada drove the round-of-16 match between France and Paraguay in Philadelphia into what forecasters flagged as potentially the hottest, most dangerous game of the entire tournament, with temperatures around 39°C and a heat index approaching 43°C. France won it 1-0, settled, tellingly, by a single Kylian Mbappé penalty in a match the conditions had slowed to a crawl. 

The cooling kit is already visible in matches, not just training. During one sweltering goalless group-stage draw in Miami, Colombia’s players pulled on ice vests at the hydration breaks while Portugal’s reached for chilled neck collars, the CLIMACOOL system and its low-tech cousins pressed into service exactly when the conditions demanded. 

Tuchel’s framing is holding up against reality in an interesting way. Despite his pre-tournament candor about suffering, now the matches are under way he refuses to change England’s style, insisting: “I’m just not ready to adapt into a different style of football because of circumstances that we cannot influence”, while still acknowledging the heat has affected training at England’s Kansas City base. England captain Harry Kane, for his part, downplayed the heat’s likely impact after heading home the winner in a warm-weather friendly against New Zealand in Tampa, played in 33°C, insisting the squad’s preparation meant the conditions “won’t be a factor”. The contrast between Tuchel’s “we will suffer,” Kane’s “it won’t be a factor,” and Vinícius’s “the game becomes very sluggish” is the whole debate in three quotes: preparation helps, confidence varies, and the heat still shapes the football. 

The heat is not flattening everyone equally, and that unevenness is itself part of the story. Even as matches slow, the tournament’s standout attacking performances continue. The Golden Boot race arrives at the quarter-finals as close as any in memory: Lionel Messi leads with eight goals, having broken a three-way tie at the top with his equaliser in Argentina’s dramatic round-of-16 comeback against Egypt, with Mbappé and Erling Haaland one behind on seven and Harry Kane on six. This is a useful corrective to any simple narrative that heat reduces all football to attrition. 

The conditions raise the physiological cost of high-intensity output for everyone, but the highest-quality players are still finding ways to be decisive within a slower game: Messi scoring the equaliser and setting up another as Argentina scored three times in the final thirteen minutes to escape a two-goal hole against Egypt, Haaland’s brace sinking Brazil, Mbappé’s penalty settling France in the Philadelphia furnace. This is exactly what the science would predict, since heat degrades sustained high-intensity running more than it degrades the brief, efficient moments of quality that separate elite attackers. Preparation and conditions shape the average; individual quality still decides matches. 

The institutional response is now visible in the fixture list itself. Both semi-finals have been scheduled into retractable-roof, air-conditioned stadiums, Dallas on 14 July and Atlanta on 15 July, an explicit choice to shield the tournament’s decisive matches from the peak of the summer heat. Scheduling, in other words, has become its own cooling strategy: the same logic as an ice collar, applied at the level of the calendar. 

The cooling breaks are also influencing matches tactically, exactly as anticipated. Former England striker Alan Shearer observed that a hydration break appeared to swing momentum in one match, allowing a team to absorb pressure and recover. A welfare measure, in other words, is becoming a tactical variable, a reminder that in elite sport, no intervention stays confined to its intended purpose.