Having reached the last 16 of the World Cup by scraping past DR Congo 2-1, one of the biggest dangers facing England in their next match against Mexico is something they can’t control – altitude.
The Three Lions will be playing at the iconic Estadio Azteca in Mexico City, 7,220ft above sea level.
It will be England’s first game at the stadium since their controversial quarter-final defeat by Argentina at the 1986 World Cup.
At that altitude, the Earth’s barometric pressure is lower, making the air thinner and meaning less oxygen is taken into the bloodstream with each breath.
Even for professional footballers, that has a potentially significant impact – increased heart rate, shortness of breath, dehydration, quicker and more intense fatigue.
By contrast, the stadium at the highest altitude in professional English football is West Bromwich Albion’s The Hawthorns, which at 551ft is 14 times closer to sea level than the Azteca.
Opponents Mexico have played all of their matches so far on home soil, and the squad is clearly used to coping with the conditions – they have played 14 games at the Azteca so far in the 2020s, scoring 23 goals and conceding only four.
Their competitive record at the Azteca is 70 wins from 89 games, with 17 draws and only two defeats. They are also unbeaten in 10 World Cup games there.
“As an opponent, you know when you go there, you are going to suffer,” says Pavel Pardo, a former Mexico captain who also called the Azteca home when he played for domestic side Club America.
So, what will the altitude feel like for players out on the pitch, how big a difference could it make, and are there any strategies to cope with it?