When the 2026 World Cup draw was held in December, coaches, players and fans all tried to discern which teams had even the slightest advantage in terms of the bracket, scheduling and travel.
But there was one other, less obvious, aspect to consider: the benefit gained by playing multiple games indoors.
The first time that a World Cup match was played inside was June 18, 1994, when the U.S. and Switzerland played to a 1-1 draw. It wasn’t much of an advantage that day, as the humidity inside the Silverdome in Pontiac, Michigan, was off the charts.
Times — and technology — have changed, however. Indoor stadiums are 100% climate-controlled, making for predictable conditions. And the use of such venues in this edition of the World Cup is unprecedented.
All told, there are four indoor venues — Atlanta, Dallas, Houston and Vancouver — that will host games, totaling 31 of the tournament’s 104 matches. A fifth, SoFi Stadium, has a roof, though it is open on the sides to allow ambient air inside. The remaining games will be played fully outdoors in the teeth of the American summer in such sticky places as Miami, Kansas City and East Rutherford, New Jersey.
This matters because there is a clear competitive advantage for teams playing indoors.
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Yes, both teams drawn into a matchup at an indoor venue are playing in the same conditions. But as the tournament progresses, teams will be in matchups in which one side played its previous game indoors and the other side played its previous game outdoors — and that could tip the scales in a significant way.
Why indoor venues may change how the World Cup plays out
Doug Casa, a professor of kinesiology at UConn, is an expert in exertional heat stroke and the CEO of the Korey Stringer Institute. The KSI conducts research into heat and hydration, injury prevention, and strength and conditioning of athletes, laborers and warfighters. Casa has led the institute since it opened in 2010, and it is named in memory of Korey Stringer, an NFL lineman who died of complications from heat stroke at the Minnesota Vikings’ preseason training camp in 2001.
Casa was unequivocal that teams playing in climate-controlled venues are much better off.
“It’s a massive, massive advantage to be playing indoors,” Casa told ESPN. “The reason being is your recovery is going to be so much easier afterwards. If you play a game like in Miami, it might be three or four days before you’re back to 95%. You get to play in Houston, Dallas or Atlanta, your recovery’s probably going to be at least twice as fast.”
The time between games at this World Cup is anywhere from five to seven days, so there should be sufficient time to recover. But that additional time will impact the intensity of training sessions after a match for at least two days. Some of the players are already coming off long club seasons, so any way that recovery can be enhanced at this point is going to be a benefit.
Casa explained that there are two concerns when playing outdoors in the summer. There’s hyperthermia — which is when the core body temperature gets too high — and dehydration. Indoors, the worry over those two conditions is significantly lessened due to the controlled temperatures and humidity.
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“You’re not going to get nearly as hyperthermic. You’re not going to be as dehydrated,” Casa said about playing indoors. “You’re going to be able to perform a lot better indoors and your recovery is going to be a lot better if you just do the same kind of normal performance.”
Suffice it to say, the draw was kinder to some teams than to others in terms of playing indoors. All told, 12 countries will play two of their group stage matches at indoor venues.
The list includes powerhouses such as Spain, Argentina, the Netherlands and Portugal. Co-hosts Canada will have the benefit of playing two matches at Vancouver’s BC Place. Cape Verde, Congo DR, Japan, New Zealand, Saudi Arabia, Uzbekistan and Sweden round out the other countries playing two group stage matches indoors.
If say, Argentina or Spain win their group, they may be able to benefit from two more games indoors during the knockout stages.
Managing the switch from the comfy indoors to the harsh outdoors
Playing in hot and humid conditions is de rigueur for players in MLS. For a team that plays its home games indoors, like the Vancouver Whitecaps, the change from playing in a climate-controlled environment to playing at outdoor venues can be jarring. Their experience can be instructive for what teams are facing at the World Cup.
“It’s definitely a challenge when you have to go play in the heat just because it’s probably like honestly 20, 30 degrees hotter there than it is here [in Vancouver],” Whitecaps striker Brian White said. “So that’s obviously an adjustment that we have to make every time we go on the road in the summer, regardless of if we’re playing inside. But definitely the change in climate from Vancouver to those places, that definitely makes it tough.”
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But steps can be taken to help mitigate the impact. White and his teammates recently experienced a road trip to Dallas and Houston, whose MLS teams play at outdoor venues. White indicated that preparation in terms of hydrating both before and after was key to recovery.
Getting athletes acclimatized to hot and humid weather is the preferred approach to mitigating negative effects. Two weeks is usually sufficient to get teams used to such conditions. But in Vancouver, that wasn’t an option.
The Whitecaps’ head of physical preparation, Jon Poli, told ESPN that the players would engage in what he called “sauna protocols” — where players sit in a sauna after training — at least two to three days a week for three weeks to help get players used to such conditions. At the World Cup that might not always be possible, but some form of acclimatization is key.
“It really is going to depend on the individual, but if it’s an individual that has never been exposed to that heat and humidity and they’re going and they’re playing their first games there, that’s going to be extremely, extremely difficult on the athletes,” Poli told ESPN.
Not every team has the resources to utilize such protocols, or the expertise in sports science. That could impact how well players acclimatize to hot and humid conditions.
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Casa added that there is a cumulative effect on players, in that they can wear down if they have to continually play outdoors in hot and humid conditions. He said there is “no question” that players are more likely to be injured in such conditions because fatigue is coming on faster for the players.
The 2024 Copa América — which was also hosted in the heat of summer in the United States — proves concerns about high outdoor temperatures are not theoretical.
During a match between Canada and Peru, assistant referee Humberto Panjoj collapsed, prompting then-Canada goalkeeper Maxime Crépeau to rush over to him and call out for medical attention. In Uruguay’s opening match of the tournament, defender Ronald Araújo left the match at halftime after he felt “dizzy” due to dehydration.
According to a paper co-authored by former U.S. Soccer Federation chief medical officer Dr. George Chiampas, who also sits on Concacaf’s medical committee, if a player doesn’t keep his core body temperature below 102.2 degrees Fahrenheit, not only is he in danger of developing a heat-related illness, but cognitive function can begin to decline.
“When you get hyperthermic and dehydrated, you’re probably more likely to make some kind of mistakes in terms of your thinking,” Casa said.
Tactics for the great — and greatly hot — outdoors
The possible physical impacts can seep into a team’s tactical approach. When playing indoors, the conditions are always the same, so it’s a relatively easy scenario for which to prepare. Outdoors there can be wind, heat and humidity, or heavy rain that can force a team to alter its game plan.
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“We have a very aggressive, high-pressing team. We have the highest-pressing height in the league,” Whitecaps manager Jesper Sorensen said. “So when we play in Houston, okay, maybe it’s also a very physical, demanding way of playing. You have to maybe take some of it away because the players will not be able to sustain it throughout 90 or 95, 100 minutes — however long the game’s going to last.
“They enforced the water break throughout the World Cup here, and that might help the players to sustain the physical level of the game, but still I think it’s something that will affect and can affect the way you approach the game, I would say.”
Based on data from ESPN Stats & Information, among teams at the World Cup, Austria (16.4 pressing sequences per game), Japan (16.4) and Belgium (15.9) had the most pressing sequences per game during World Cup qualifying. Data from TruMedia shows that Spain and the Netherlands ranked second and third worldwide in terms of average possession start position from their own goal, with marks of 47.6 and 47.0 yards, respectively. Japan allowed just 3.6 passes per possession.
Such numbers hint that these teams are more aggressive defensively and could benefit more than most by playing multiple games indoors.
The tournament is just now entering its second week, so it’s likely that the impact won’t be entirely clear until the knockout rounds. But it will be worth noting how well the presumed heavyweights do, and if the intensity with which they play stays consistent or drops over the course of the tournament — especially as it relates to whether they are playing outdoors or indoors.
