"There is a bit of a myth that you've got 24 hours of grace when you get out to altitude, before it has an effect," Maxwell said.
"Your body starts reacting to the hypoxia, to the altitude environment, straight away. Within six hours, they're going to be feeling the effects of this."
The physical environment also alters ball mechanics.
Professor Barton Smith, a mechanical and aerospace engineering expert at Utah State University, noted that air density in Mexico City drops by approximately 25% compared to sea level, lowering aerodynamic drag.
"But, I would be surprised if that has a large effect on the game, especially for short shots," Smith said.
However, lower air density directly suppresses the Magnus effect, which dictates how a spinning ball curves through the air.
A reduced Magnus effect means shots will bend significantly less.
"When the ball moves less, there cannot be as much finesse to shots," Smith said.
Historical data favors teams accustomed to these elevations.
Neal pointed out that high-altitude teams consistently score more and concede fewer goals, gaining roughly a half-goal advantage for every 1,000 meters of altitude difference, particularly in the second half.
Conversely, previous training in warm climates offers a slight physiological advantage. Maxwell noted that heat adaptation provides a cross-adaptive benefit that helps athletes cope with altitude environments.
"For a team such as England, with medical support and careful preparation, the greatest concern is likely to be the physiological strain caused by hypoxia [low oxygen availability] and the effect this has on workrate, recovery and decision-making rather than any major health risk," Maxwell said.
