Altitude Acclimation for Endurance Athletes

Post contributed by Coach Maria Simone. Photo (L to R): Melina Grudzinski, Clarissa Ramos, Maria Simone, and Sally Kado atop Mt. Elbert, the highest peak in Colorado at 14,439 feet.

I went to high altitude for the first time when I ran the Rim-to-Rim-to-Rim in the Grand Canyon in 2015. The rims themselves sit at 7500-7700 feet, while the base of the Canyon sits at 2000-2500 feet. I could feel the squeeze on my lungs, as I struggled to hit even a 30-minute mile as I climbed to the top at the end of our day. Higher altitude also complicates our ability to eat and drink, so I found myself puking as the day went on. I struggled to keep the calories and hydration in. 

Since that first trip to altitude, I’ve learned much about preparing for and performing at altitude. And, even though I now live at 9200 feet, I continue to make adjustments in terms of pacing, hydration, and fueling. Even if you are acclimated, altitude still has impacts. 

Many iconic and destination races, especially for trail running, happen at high altitudes. Yet many of the athletes come from lower elevations. So, if you are one of these athletes, you may be wondering how you can prepare for a high-altitude race when you live at sea level. 

What is Altitude? 

Most simply: altitude is the distance above sea level. Most humans will feel the impacts of altitude on performance starting around 5000 feet. However, it’s important to note that this can vary, and some report feeling impacts of altitude starting at 3000 feet. 

The Society of Mountain Medicine classifies high-altitude terrain as such: 

• High Altitude – 4,900 to 11,500 feet
• Very High Altitude – 11,500 to 18,000 feet
• Extreme Altitude – above 18,000 feet

These altitude regions relate to differences in atmospheric pressure, which falls as we rise in altitude. Interestingly, the amount of oxygen in the air is the same throughout the atmosphere, but the atmospheric pressure impacts the concentration of oxygen and the pressure in the lungs, which in turn impacts inhalation, exhalation, and gas exchange. 

This is what makes all the difference in how we can train and race in thin air. Our body has to work harder to get the oxygen where it needs to go. And, we can’t produce energy during endurance efforts without oxygen. 

Effects of Altitude on Performance

Altitude is a chronic adaptation, meaning it takes an extended period of time for the body to acclimate. Altitude leads to decreased hemoglobin saturation in our blood, which is responsible for oxygen delivery from our lungs to our muscles. 

We begin to feel the effects of this usually about 24 hours after arrival at altitude. As the body adapts to reduced oxygen saturation in the blood, it produces more red blood cells, but this process takes time. Research suggests that acclimatization is about a 3-week process, and the benefits of altitude training can last for about 2 weeks upon return to lower elevations. 

What Happens to Your Body at Altitude?

You are likely to feel the worst effects between 24 to 72 hours after arrival. But, you will continue to feel some symptoms for as long as 3-4 weeks, and some symptoms (like increased respiration) may never change no matter how long you stay at altitude.  A few things happen when the body gets to altitude: 

• Increased resting heart rate
• Decreased maximal & threshold heart rate, and VO2max
• Decrease in blood plasma (which lends to the increase in HR, as well as generally feeling crappy)
• Increased respiratory rate at rest and in training
• Change in pH balance
• Fatigue/daytime sleepiness (some report trouble keeping their eyes open)
• Slower pace and/or lower watts for the same or higher rating of perceived exertion (RPE) and heart rate.

Symptoms of Altitude Sickness, or Worse, “HAPE”

While some symptoms are normal and don’t indicate danger, other symptoms may indicate altitude sickness. Symptoms of altitude sickness include: 

• Dizziness
• Nausea & Vomiting
• Headache
• Increased HR
• Trouble sleeping
• Nosebleeds
• Rapid heart rate
• Loss of appetite
• Shortness of breath
• Congestion
• Numbness or tingling in the hands & feet

High-altitude pulmonary edema (HAPE) is a reaction to altitude that can be life-threatening, and most commonly occurs at 8,000 feet or higher, although it is not impossible to experience HAPE as low as 5000 feet. 

Acclimatization takes time, and people who ascend to high altitudes too quickly may not have enough time to adapt. This can lead to a build-up of fluid in the lungs, which can make it difficult to breathe. Symptoms of high-altitude pulmonary edema include: 

• Shortness of breath
• Rapid breathing
• Cough
• Fatigue
• Chest pain
• Cyanosis (a bluish tint to the skin)
• Confusion
• Loss of consciousness

If any of the above altitude sickness symptoms (HAPE or basic altitude sickness) worsen or become severe, you should get down in elevation as much as possible and seek medical assistance immediately. 

How to Train for High Altitude

The good news is that the body can acclimatize to high altitude, and even if you live at sea level there are training interventions you can do before you travel to support how you feel and your performance. The primary limiters at altitude relate to oxygen delivery and gas exchange in the lungs. As such, it makes sense to do things in training that will improve blood plasma volume, red blood cell production, and efficiency for oxygen delivery. 

Sleep High Train Low

The “sleep high, train low” philosophy is one option if you have access to altitude within driving distance. In this approach, you sleep at high to extreme altitude but train at lower elevations. By training at lower elevations, you can train harder, since the body cannot work as hard at altitude as it can at sea level (or lower altitude). 

For example, I live at 9200 feet, and I have the option to get as low as 5500 feet within a 30-minute car ride. So, I tend to do speed work at those lower elevations. By doing this, I am able to run faster, and with more strength, for a lower heart rate cost. My body reaps those benefits, while also remaining acclimatized to altitude. 

If you don’t have access to high altitude, you can look into an altitude tent for sleeping. But, these apparatuses can be very expensive, and also disruptive to sleep (and home life). But, it is an option that has research to back its efficacy. What does not work are the oxygen-restriction masks. They do not make any adaptations relative to altitude. They just make it harder to breathe. 

Get as Fit as You Can

Of course, sleeping at altitude or in an altitude tent isn’t a practical option for most of us. Another option, available to all, is to get as fit as you can prior to the event. This training may include high-intensity intervals to support and promote changes related to oxygen delivery and uptake, as well as red blood cell growth. 

The other part of this equation is good-old steady-state aerobic training. Taking a polarized approach like this can help you feel better at altitude due to the training adaptations that support plasma volume production, cardiac output improvements, and the density and functioning of mitochondria. 

When your departure date gets closer, you want to reduce fatigue and stress as much as possible. In practice, this may mean an earlier taper. In the 5-7 days prior to travel to altitude, avoid high-intensity training, eat nutrient-dense foods, remain well-hydrated, and ensure your iron levels are good. Athletes with anemia or low iron levels should consult with their doctors well in advance of the trip and the race to discuss options. 

Heat Acclimation for High Altitude

Some research studies show that a heat acclimation protocol may be useful for reducing the energy cost of aerobic exercise at altitude. This is due to the ways in which heat acclimation will support more effective oxygen delivery, increase in plasma volume, and improve thermoregulation. However, there is not overwhelming evidence to indicate that the cost of heat training produces enough reward for racing or training at altitude. However, it is an option to consider during low training load weeks leading into a high altitude event. 

Traveling & Racing at Altitude

The worst symptoms from altitude tend to come between 24 to 72 hours after arrival. Given this, the general recommendations for racing at altitude are to arrive either one week before, or the day before the event. Either of these options will help you avoid the worst effects of adapting to altitude. 

As we’ve discussed previously, your effort at altitude will be different than your effort at sea level. So, you will need to adjust accordingly by adjusting expectations for pace and power. Rate of perceived exertion is instructive, as it helps adjust your output to sustainable efforts. While training for your event, take note of how your body feels so you can make wise choices during your event. 

You can also use heart rate, keeping in mind that your max heart rate will be depressed at altitude, which in turn causes a shift in your lactate threshold heart rate. So, your zones may shift downward by anywhere from 5 to 15%. Even if you are acclimatized, you will still be slower and/or hold less power at altitude than you do at lower elevations. 

You can also consult pace and power conversions for altitude. When using these types of calculators, be mindful that they cannot take into account individual responses to altitude. So, the impacts will vary from person to person. Some calculators to consult include: 

• Final Surge (goes up to 8000 feet)
• VDot Calculator (will help you estimate pacing for intervals and races; select the “advanced” feature to add altitude)
• Chart of % changes in power at different altitude levels 

Generally speaking, we lose about 4-5 seconds per mile for every 1000 feet we go above 3000 feet.So, at 4000 feet, we would run about 4-5 seconds slower than we do at sea level. For example, at 8000 feet, we would run about 25 sec/mile slower than we do at sea level. 

For power on the bike, the estimates are about 1% for every 1000 feet, but in practice, I find it is actually a little higher than this for initial days at altitude. It may be more like an 8-10% decrease in FTP at 5000-6000 feet. What the above times do not account for, however, are changes in terrain and conditions. If your race is on substantially hillier, more technical, or otherwise challenging terrain, pacing will be further impacted. 

At altitude, your recovery times will be slower. As such, if you are doing a training camp or several-day stage race, bear in mind that you will need to be more aggressive in your recovery protocol to ensure the ability to get up the next day and do it again. 

Finally, stay on top of your fueling and hydration! It can be hard to eat at altitude, so if you normally eat in 20-minute intervals, at altitude, you may have to take in smaller amounts every 10 minutes instead. There is some evidence to suggest that we have higher caloric needs at altitude, so be mindful that you may need more calories than you typically do. Make sure to hydrate with electrolytes. High-altitude locations are often quite dry, and you might not always realize you are sweating because it evaporates quickly. 

Racing or training at altitude can be a humbling experience. But, it is assuredly quite beautiful as well. You will experience amazing views, see the purple mountains’ majesty, and learn what an amazing machine the body can be.