Can England handle Mexico's altitude? Why caffeine...

Harry Kane, Jude Bellingham, caffeine and beetroot juice -- if England are to beat Mexico and overcome the punishing effects of playing at high altitude in Mexico City on Sunday, they will need all those ingredients and more to reach the World Cup quarterfinals.

>Having advanced to the round of 16 by playing in air-conditioned stadiums in Dallas and Atlanta and in wet conditions in Boston and New Jersey, England coach Thomas Tuchel said it will be "impossible" to overcome the "big disadvantage" of facing Javier Aguirre's side at the Estadio Azteca, which sits around 7,220 feet above sea level.

>Though Mexico can rely on passionate home support, it is the challenge of playing at altitude that proves most difficult for visiting teams. And with England arriving in Mexico City on Friday, landing only 49 hours before the scheduled kickoff Sunday, Tuchel's players will have had no time to sufficiently acclimatize to the conditions.

>El Tri have a formidable record at the Azteca, which was the venue of England's 1986 World Cup quarterfinal defeat against Diego Maradona's Argentina. Since 1966, Mexico have lost just twice in 89 competitive fixtures at the Azteca, with both losses coming in World Cup qualifiers against the United States and Honduras in September 2013.

>So what problems will England face and how can they minimize the impact to give them a chance of success?

>ESPN spoke to Steve Magness, who is the author of "Win the Inside Game" and a high-performance expert specializing in kinesiology and exercise physiology, about the problems England must overcome in Mexico City.

>This interview has been lightly edited for clarity.

>Magness: Here's the thing -- regardless of how fit you are, how well-trained you are, you go up to 7,000 feet and your body's going to respond. Your breathing rate naturally goes up a little bit, your heart rate goes up a little bit, your cardiac output goes up a little bit to compensate, all because your blood oxygen saturation is dropping.

>Normally, the blood oxygen rate is around 98% for everybody, but the second the team gets off that plane, even just standing around, it will drop to probably 91%, 92%.

>And once you add in those sprints, it's dropping even lower. Some of these symptoms are just unavoidable, and it's going to suck. You do everything you can to prepare, but you also have to just acknowledge that it's going to suck and we're just going to have to deal with it.

>It's like that point in a marathon, where even if you're [world-record holder] Eliud Kipchoge, it's going to be miserable and you've just got to put your head down and be like, "Well, it's miserable. Let's go at it."

>Magness: It's incredibly challenging, because in football you need endurance, and speed, and speed endurance.

>It's like a combination of a distance runner and a sprinter. If we're talking just endurance, we're looking at a 10% drop in VO2 max [maximum oxygen consumption], which would be a performance decrement of 3% to 4%.

>In running terms, it's like taking an elite athlete who's trying to break the mile world record by running 3 minutes, 43 seconds. If you put him at 7,000 feet altitude, he probably runs around seven or eight seconds slower, which takes him from trying to break the world record to being an also-ran in a non-elite race. So, it's a huge effect.

>Magness: Physiologically, going in last-minute, in and out, makes sense. But when we include flying to another country and all the logistics that come with it, that's where it runs into problems.

>With England's limited time frame -- they simply couldn't spend three weeks acclimatizing in Mexico -- you're looking at a trade-off because the closer you come into game day, you have to question how much your preparation is disturbed.

>"Is our sleep disturbed from coming in maybe only a day before? Are our legs tired because we've been sitting on a plane?" Being sedentary has an effect because you feel flat, as you've been sitting in a chair constrained.

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>Physiologically, it kind of sucks to come in two days before, but if you do it even more last-minute, then physically, mentally and emotionally, you don't have the necessary routine to prepare.

>But the reality is that the players are going to adapt differently to the altitude effects. Yes, they're all England players, but you have a diverse squad, which means their individual physiology is going to differ.

>For instance, if you took a random American and you took an American with Kenyan background, their blood will respond differently to going up to 7,000 feet altitude. So, when you take a squad of 26 people, the reality is you're going to have a bunch of different physiological responses even though they're at the exact same altitude when they get off the plane.

>Magness: Fueling up with carbohydrates and sodium bicarbonates is a must, as is doing everything possible to help with sleep patterns, but beetroot juice can be a very useful addition, too, because it is something that can be even more helpful at altitude because it counteracts one of the things that we know occurs.

>When you go to altitude, especially in the first couple of days, you get a loss in blood volume. The way I like to think of it is, instead of a smooth flowing stream of water, blood becomes more sludge-like.

>And what beetroot juice does is dilate the blood vessels -- it opens them up so we get that more free-flowing fluid in there, so you can deliver oxygen. If I was doing this trip, it would be something that I definitely would look into.

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>Magness: If they're smart, England are going to use those breaks as a time to take on caffeine. If you're in the marathon, what do you do? You take some targeted sugar and fuel, but often targeted sugar and fuel that has caffeine in it because you know at some point in the marathon, it's not just physical -- your brain's going to go to mush. The caffeine can boost you.

>The hydration boosts are essentially a "fill me up, kick me in the rear and get me going a little bit."

>As the game wears on, as you get tired, as you get fatigued, your perception of just how difficult it is goes up partially because of altitude. So somewhere in that 60- to 80-minute range in the second half, part of your body is going to scream at you that you're tired, you're fatigued, slow down. What caffeine does is it essentially perks you up and it acts as a stimulant that makes it feel just a little bit easier.

>Magness: Mexico has one of the biggest home-field advantages in sport because of the conditions in Mexico City. They are accustomed to everything; their opponents aren't.

>The best analogy I can give it is that if we took Josh Kerr, the British middle-distance runner, and said, "Hey, your next Olympic Games are in the Rift Valley in Kenya, have fun."

>Of course, he'd still be competitive and he'd still have a shot because he's world-class and will be prepared for it, but he'd be at a disadvantage. There would definitely be a home-field advantage for the Kenyan athletes.

>But England has a shot. The altitude certainly makes it an uneven playing field, but winning is not impossible.