Mexico vs England: Thomas Tuchel's side face a huge altitude problem by playing World Cup round of 16 at 7,000 feet

"It is one of the most beautiful fixtures you can have playing Mexico in the Azteca," said Thomas Tuchel after England booked their World Cup last 16 spot. But it is also one of the hardest fixtures in football.

England go to the 87,000 Azteca Stadium full of joy after Harry Kane's heroics against DR Congo - but not only do they have to play better against the co-hosts, they will be as testing an environment as they have faced in a generation.

Mexico's record at their national stadium is phenomenal: in 89 competitive fixtures there, they have lost just twice and are unbeaten in 13 years. No World Cup team has beaten Mexico there in 10 attempts.

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But the biggest problem is not the raucous Mexico crowd, nor the national team's excellent record there. England's biggest challenge? How do they survive the altitude?

The Azteca Stadium sits over 7,000 feet above sea level. That's one-and-a-half times higher than the summit of Ben Nevis, which is the United Kingdom's highest point.

"If this was played anywhere else, England would win this football match," said Paul Merson to Sky Sports. "No Mexico player gets in the England team - we're by far the better team.

"But altitude at 7,000 feet? It's mind-blowing."

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Playing at higher altitude matters. It affects your breathing, as less oxygen gets into the body, while it can lead to higher heart rates and a quicker route to fatigue. The thinner air can also affect the spin and movement of the ball.

"You have to really judge it right in altitude - it's really hard on the body physically," Sol Campbell told Sky Sports News this month.

And the tricky thing for England is you cannot master altitude training in three days. "England can't do anything," added Merson. "It takes a couple of weeks to get acclimatised. That is the biggest, biggest obstacle for England."

"It's great if you're there for two weeks, you're flying," added Campbell. "But if you're parachuted in there, you have to time it right. It can take a lot out of your energy, it can sap a lot out of you."

Even Tuchel knows it. "My understanding is we cannot adapt to the altitude," said the England boss after beating Congo.

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"It's a huge advantage Mexico will have. We have three days in between the [Congo and Mexico] matches and we cannot adapt to it. We knew that before. It's just a disadvantage, for which we will have to deal with."

Mexico, unlike England, are well used to the conditions. As well as playing in the capital on a regular basis, the co-hosts have already had three games at the Azteca at this tournament - the group wins over South Africa and Czech Republic, and the last-32 victory over Ecuador.

Compare that to England,. The last time they played a match over 7,000 feet was also their last trip to the Azteca - for the 1986 World Cup quarter-final with Argentina.

That game was known for Diego Maradona's 'Hand of God' - but it also saw the Argentine superstar dance and hurdle over England players in the heat for his other mesmerising goal.

The last time England played above 4,000 feet was at the 2010 World Cup, where they played two games in South Africa against the USA and Germany.

Despite Fabio Capello taking his team on a high-altitude training camp before the tournament, England still didn't manage to win either of those two games.

England will have to rely on their extensive warm weather training to try and counteract the latest challenge. "We came very early to the country and to the US, we banked good heat training into our bodies," said Tuchel. "That was the idea behind it.

"The players have lots and lots of heat training which will help them. The heat and humidity is not the problem. We are used to that."

England are going to have to rely on their individual quality to get over the line. They are going to need Kane at his best.

"Mexico in Mexico is as big as it gets in the World Cup," said Kane after the Congo match.

"The atmosphere is going to be incredible and tough for many different reasons. If you want to be world champions, you have to go through tough games."

There may be tougher opponents, but it is hard to think of a more difficult environment.