As the English football team prepares for its FIFA World Cup Round of 16 match against Mexico on Monday, manager Thomas Tuchel will have another set of numbers on his mind apart from his team’s 4-2-3-1 formation — 2240.That’s the altitude of Mexico City’s Estadio Azteca, which poses the biggest, or rather highest, hurdle for a team looking to set up a quarter-final clash with Brazil or Norway.The altitude is Mexico’s greatest ally as the rarefied air can impede the English players’ oxygen intake. And England had little possibility of acclimatising to that height with just a four-day turnaround time after their Round of 32 match against the Democratic Republic of Congo.Tuchel, therefore, has leaned into a counterintuitive tactic — leaving arrival in Mexico to the last minute, or 48 hours, as FIFA mandates. This is not an exact science, but Tuchel wants to reduce the inevitable damage from the altitude disadvantage.Mexico, meanwhile, has won all four of its World Cup matches at the Azteca, netting eight goals and conceding none.Why is the Azteca so challenging?To begin with, its altitude. At 2,240 metres above sea level, the partial pressure of oxygen falls by roughly 20%, reducing the amount of oxygen available with each breath.The lower pressure reduces the number of oxygen molecules in the air, thus lowering aerobic capacity and making breathing heavier. With less oxygen entering the bloodstream, the body tries to ensure enough supply to muscles while putting pressure on the lungs. Decision-making, like physical performance, also depends on adequate oxygen supply to the brain. Thus, a slower recovery time could hamper actions such as counterattacking runs.Story continues below this adAlso Read | Forget Maradona’s ghost, England’s real Azteca problem is Mexico’s defenceMexico has played all but one of their four games at the Azteca, and travels from a base only 15 minutes away. Their pre-tournament camp would have helped even the majority of the squad who don’t all live at altitude. They also have a formidable record at the Azteca — 70 wins, 17 draws and two losses.A landmark 2007 study published in The BMJ, which analysed 1,460 international matches in South America over a century, observed that teams accustomed to living and training at high altitudes tended to perform better when playing at low altitudes, likely due to long-term physiological adaptations such as greater oxygen-carrying capacity.What are the immediate effects of playing at such a height?Story continues below this adTeams are likely to rely more heavily on substitutions in the second half and run fewer kilometres. A half hour into the game, high presses may feel daunting, fast sprints and quick turns will test the lungs, and the risk of dehydration is imminent. England players celebrate after the World Cup round of 32 soccer match between England and Congo in Atlanta on July 1. APWhile the running itself might feel unimpeded because of less resistance, sharp intake of breath between accelerations during recovery is a common symptom. British high altitude runner Callum Elson told The Independent: “Recovery is key — that idea of trying to catch your breath, trying to let your heart rate get back down, once it’s up, it literally just doesn’t come down.”How does the ball travel at over 2,200 metres?The BMJ study mentioned above noted a reduced air resistance due to thinner air, meaning that shots and long passes travel faster, farther and with less spin, requiring players to adjust their technique.Ahead of the 2010 World Cup, an Adidas study estimated that a free kick at high altitude could reach the goal up to 5% faster than the same kick at sea level.Story continues below this adThis has posed a worry for England goalie Jordan Pickford, and his defenders, Marc Guehi, Ezri Konsa and Djed Spence.But Mexico, which has been scoring through long-range goals, can falter on set-pieces.Aside from altitude, the home team’s other advantages will be the humidity, the noisy crowd — and the ghost of Diego Maradona. This, after all, was the stadium where the Argentinian great scored his (in)famous ‘Hand of God’ goal.Why did Tuchel choose to get in so late?The BMJ study notes that lowland teams cannot fully acclimatise to playing conditions at an altitude in a brief period. Recommendations from football medical authorities have suggested around 10 days of acclimatisation for matches above 3,000 metres.Story continues below this adSuch preparation, however, is often impractical in modern tournament schedules. England, for instance, just had a four-day turnaround time.English sides in the past have attempted to acclimatise differently to elevated playing conditions ahead of crucial matches. The rugby team once opted for a late arrival in Johannesburg (1,753m) under Eddie Jones. Legendary football coach Sir Bobby Robson took the English squad to Mexico a year ahead of the 1986 World Cup to familiarise the team with the conditions. Both teams lost anyway. Mexico players celebrate after the World Cup round of 32 soccer match between Mexico and Ecuador in Mexico City, Tuesday, June 30, 2026. AP/PTITuchel has pragmatically chosen to accept the disadvantage. Mercedes’ F1 driver George Russell has echoed this logic, telling German news agency DPA International: “Sleeping you feel your heart rate is elevated and you feel a bit breathless…try and arrive as late as possible, and leave as soon as possible, because you don’t sleep that well.”This could affect running. “Getting there late is the best thing. You want to go into those 90 minutes being as fresh as possible. Any extra hour you are there your body is not in as good a place,” Russell said.Do effects of altitude linger?Story continues below this adThe effects of a short stay at altitude do not usually linger after descent. Symptoms of altitude illness typically improve within hours to a couple of days, according to the CDC Yellow Book. However, athletes who live or train at altitude can retain physiological adaptations, such as improved oxygen-carrying capacity, that may continue to benefit performance after they return to lower elevations.While conquering Azteca might be a glorious challenge, England are obviously aiming further — heading towards Brazil/Norway in Miami heat. Elson told The Independent, “If they get through, how absolutely exhausted are they going to be afterwards? Even if they manage in the moment with adrenaline… the after-effects of how they recover will be the really hard bit.”