One mile is 5,280 feet in distance. That just happens to be the exact elevation of the city of Denver where Empower Field at Mile High sets the stage for Broncos home games. The human body performs differently at different elevations and it has the ability to adapt to these changes, but those adaptations take time to occur.
According to varying sources, it can take between nine and 18 days to fully acclimate to Denver’s elevation when coming from a lower elevation. Because the rigorous NFL schedule sends teams from place to place almost weekly, it’s impossible for any team other than the Denver Broncos to remain fully acclimated to such a high elevation.