Is Altitude a Real Home Field Advantage?

Visiting teams arrive in Denver talking about the air. They arrive in La Paz talking about the air with considerably more feeling. The question is not whether thin air does something to a body. It is whether that something shows up in the result.

McSharry's analysis in the BMJ (2007) covered 1,460 international football matches across ten South American countries and more than a century. High-altitude home teams won more often, the goal-difference advantage grew with elevation, and visiting sides from low altitude fared progressively worse the higher they played. It is the single strongest outcome-level result in the field.

Pollard's review of home advantage in football calls the phenomenon an unsolved puzzle, with crowd effects, referee bias, travel fatigue, territoriality and venue familiarity all independently documented. Home advantage exists at sea level too. Altitude cannot be the mechanism for a thing that happens everywhere.

The confounding is geographic. Denver's opponents fly further than most, from lower and often coastal cities. La Paz is not merely high; it is a long way from everywhere. Every altitude study to date compares venues that differ in more than one variable.

And acclimatisation matters: aerobic decrements attenuate over days to weeks, so a genuine physiological effect should shrink for teams that arrive early — a variable retrospective outcome studies almost never control.

The dose-response pattern in McSharry's data is the best argument that something physiological is genuinely in there. Crowd hostility and travel distance do not obviously scale with metres above sea level; oxygen availability does, and the measured advantage tracks it.

Comparing identical visiting rosters at the same venue under different acclimatisation windows — days versus hours before kickoff — would isolate physiology from everything else. So would models controlling simultaneously for travel distance, rest days, crowd size and referee assignment. Closed-crowd fixtures at altitude venues offer a natural experiment nobody has fully exploited.

The VO2max studies establish that unacclimatised individuals lose aerobic capacity at altitude. They do not measure how many points that costs a professional team. That inferential step is assumed, not tested — and the baseball findings are about projectile aerodynamics, which do not transfer to sports where the mechanism would have to be human.