Your first run in the mountains is humbling. Maybe you flew into Denver for a race, or drove up to Flagstaff for a training camp. Back home in Houston or Miami, you cruise through five-minute miles. Here, at 7,000 feet, you’re gasping after 400 meters. Your legs feel fine. Your lungs are screaming.
You’re not out of shape. You’re simply not acclimatized.
This exact effect has fascinated elite athletes for decades. The body responds to altitude with remarkable adaptations. Some of them can be harnessed to become faster, more enduring, more capable. Others just make life miserable.
The question is: What’s actually happening up there? And why do some pro athletes voluntarily sleep in tents that starve them of oxygen?
The Day All the Records Fell – and Others Didn’t
Mexico City, 1968. The Olympic Games take place at 7,350 feet. For most athletes, an unfamiliar burden. And then something strange happens: In the sprints, world records shatter left and right. In the distance events? Times significantly worse than previous Games.
Sounds contradictory at first. Same altitude, same conditions – but completely different results. The explanation lies in physics and in how our bodies generate energy.
Thin Air Isn’t Actually Thin
A common misconception: There’s less oxygen in the air at altitude. Not true. At 10,000 feet, the air contains exactly as much oxygen as at the beach – about 21 percent. The difference is air pressure.
Think of it like squeezing a sponge into water. With lots of pressure, it soaks up plenty. With little pressure, it barely absorbs anything. Your lungs work similarly. At lower air pressure, less oxygen gets “pushed” into your blood. The oxygen is there – it just has a harder time getting in.
This explains the sprinters in Mexico City. Short, explosive efforts barely need oxygen. The energy comes from other stores. Instead, they benefit from reduced air resistance. The air really is less dense at altitude. If you’re only running for ten seconds, you don’t notice the oxygen deficit – but you definitely notice less headwind.
Distance runners face the opposite problem. Their muscles scream for oxygen, and they’re not getting their usual supply. Every stride feels heavier. Legs fatigue earlier. Times suffer.
The Body Improvises
When conditions change, the body has no choice but to adapt. This adaptation is called acclimatization. And it kicks in faster than you might think.
The first response is simple: Your heart beats faster. When each breath delivers less oxygen, the body just pumps more blood through the system. At the same time, you breathe deeper and more frequently. Minute ventilation increases – a technical term meaning more air flows through your lungs.
These are emergency measures. Effective short-term, exhausting long-term.
The more elegant solution takes time. After one to two days at altitude, your body starts producing more red blood cells. These little transporters are responsible for carrying oxygen in your blood. More transporters means more capacity. The hormone that drives this production is called erythropoietin. Sounds complicated, but you probably know it by its abbreviation: EPO.
Yes, that EPO – the one that fueled cycling scandals for years. At altitude, your body produces it completely naturally.
Why Elite Athletes Disappear into the Mountains for Weeks
Here’s where it gets strategic. The increased production of red blood cells sounds like a legal performance booster. And it basically is. But there are catches.
First: The adaptation needs several weeks to become truly effective. A weekend trip to the Rockies does practically nothing. Sports medicine experts recommend multi-week stays to achieve the desired effects.
Second: Training at altitude is harder than usual. You can’t go as hard as you can at sea level. Anyone doing the same tempo runs at 7,000 feet as at sea level risks overtraining or simply gets slower.
Third: As soon as you come back down, your body realizes it has too many red blood cells. And starts breaking them down.
The Timing Problem – More Complicated Than You’d Think
The classic recommendation: Race one to two days after returning from altitude. There’s a good reason for this. Once you’re back at sea level, your body registers the oxygen surplus and shuts down EPO production. Then something called neocytolysis begins: The body actively breaks down its youngest red blood cells – precisely the ones you just produced.
Between days three and ten, many athletes experience a noticeable performance dip. Breathing is still programmed for altitude, plasma volume fluctuates, and anyone who trained up high for weeks is missing their top-end speed. Coaches sometimes call this phase the “Valley of Death.”
Interestingly, a second window opens after about two weeks. Breathing, plasma volume, and coordination have stabilized. Yes, some of those extra blood cells are gone. But the mechanics work again. Many world records have been set in this later window.
The short version: Race either immediately after returning or with at least two weeks of buffer. Everything in between is a lottery with bad odds.
Live High, Train Low – Having Your Cake and Eating It Too
Sports medicine has developed various approaches to get the best of both worlds.
The most popular is called “Live High, Train Low.” The idea: You live and sleep at altitude so your body produces more red blood cells. But you train at lower elevations where you can work harder. The altitude tent in the bedroom is the logical evolution of this concept. Lance Armstrong made it famous – he slept in a tent that artificially reduced the oxygen content of the air.
In his book, he describes trying to sleep in it with his wife once. After three hours, an alarm went off: Oxygen levels had dropped so low the system flagged danger. They were rudely awakened. Not exactly cozy.
The opposite would be “Live High, Train High” – everything at altitude. Body and training are permanently exposed to the changed conditions. Effective, but intense.
And then there’s “Live Low, Train High” – normal life in the valley, but individual training sessions at altitude. More realistic for most people, but less effective.
Altitude Chambers and Other Workarounds
Not everyone has mountains in their backyard. And not everyone can disappear to Flagstaff or Mammoth Lakes for weeks. So technology stepped in.
Altitude chambers simulate high-altitude conditions without anyone leaving the building. Air pressure is artificially lowered, oxygen deficit induced. Everything controlled, everything adjustable. No surprise temperature drops, no dangerous UV radiation, no mountain goats in the way.
You can even simulate altitudes up to 20,000 feet. Way more than useful for normal training. But for special preparation – say, for a race at high altitude – definitely handy.
Breathing masks work similarly but differently. Instead of lowering air pressure, they reduce the oxygen percentage in inhaled air. The result for your body is comparable: less oxygen, more adaptation pressure.
When the Mountain Fights Back
Altitude sickness is real. Headaches, nausea, loss of appetite, sleep problems. Anyone who ascends too quickly or trains too hard up high risks exactly the symptoms that negate any training benefit.
The body needs time. Acclimatization isn’t a switch you can flip. It’s a process that requires patience. And respect for your own limits.
The Line to Doping
An interesting question remains: Isn’t altitude training basically legal doping?
The short answer: No. Natural EPO production at altitude is permitted. It’s a physiological response to changed environmental conditions. No different from sweating in heat or shivering in cold.
What’s not allowed: Injecting EPO from outside. Putting in what the body is supposed to produce itself. That’s the doping method that plagued cycling for so long.
Blood doping is also banned. The concept: During altitude training, blood is drawn – enriched with all those extra red blood cells. These blood bags are stored and transfused back into the athlete later, ideally right before a major competition. Sounds clever, but it’s illegal and punished with suspensions.
What Remains
Altitude training isn’t a magic bullet. It’s demanding, expensive, time-consuming, and completely overkill for most recreational athletes. But for pros, especially in endurance sports, it’s become almost indispensable. To compete at the world-class level today, you have to do altitude training. Not an option. A necessity.
That first gasping run in the mountains? It’s just the beginning. The body adapts. Given enough time, enough patience, and the right strategy, what once left you breathless becomes your edge.