Altitude, Its Effect on Performance & Steps You Can Take to Perform at Your Best

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How Altitude Affects Performance

By Chris Carmichael

Founder and Head Coach of CTS

With athletes coming to Colorado Springs, Colorado from far and wide to compete in the 4-day Pikes Peak APEX mountain bike stage race, everyone wants to know how to prepare for and race well at altitudes between 6,000 and 10,000 feet above sea level. Here is what you need to know about altitude, its effect on performance, and the steps you can take to perform at your best.

The effect of altitude exposure

As you go up in elevation, the composition of gases that make up the air around you remains the same as it was at sea level: 20.93% oxygen (O2), 0.03% carbon dioxide (CO2), and 79.04% nitrogen. What changes is that there’s a decrease air density, and hence a decrease in the partial pressure of oxygen, and your lungs rely on a pressure gradient for gas exchange between your lungs and bloodstream. Basically, there isn’t ‘less air’, there’s less oxygen in a lungful of air due to changes in partial pressure at higher elevation.

For most people the effect of altitude becomes noticeable at elevations above about 5,000-6,000 feet. What you’ll notice immediately is that your breathing rate and heart rate increase, at rest and any submaximal exercise intensity, including walking up a flight of stairs. Heart rate increases because of hemoconcentration – your body reduces blood plasma volume from 10-25% in order to increase the concentration of oxygen-carrying red blood cells. Decreasing blood volume decreases stroke volume (the amount of blood pumped out of the heart per beat), and your heart rate has to increase to maintain normal cardiac output.

Breathing rate and depth increase to compensate for the lower partial pressure of oxygen in each lungful of air. And while it may be noticeable, breathing a little more quickly is rarely a limiting factor for performance (at this moderate altitude). It is, however, an important stimulus for the short- and long-term adaptations to altitude. Increased respiration means exhaling more CO2 than normal, which lowers the pH of blood. The kidneys respond to this by increasing urine output, which is part of the way plasma volume gets reduced. In the long term, which takes about three weeks, the kidneys respond to hypoxia by producing and releasing more erythropoietin to increase production of red blood cells.

What to expect when coming to altitude

Expect to your sustainable power at lactate threshold to decline by about 10% compared to sea level at altitudes above 6,000 feet. There will most likely be more of a decline as you go even higher, especially above 9,000 feet. However, everyone responds to altitude differently. Some riders will see less of a decline in power output than others. Heart rate response is likely to be elevated at a given perceived exertion or power output, at least in the early days when you are fresh. As the race progresses, heart rate response may change with fatigue, dehydration, sleep quality, etc. If you are unfamiliar with how your body responds to altitude, perceived exertion is going to be your best gauge of intensity and pace. While perceived exertion is low tech, it is remarkably accurate and you are much better than you think at determining what is and isn’t a sustainable intensity. 

The most dramatic difference you will notice about performance at altitude is how it affects your ability to dig deep for efforts above lactate threshold. Conservative pacing is the key to success at altitude. When you dig deep at 10,000 feet you will more quickly reach the point where demand energy faster than your aerobic system can deliver it. You’ll reach lactate threshold at a lower power output than you are used to. The problem is that producing energy above lactate threshold is like buying with a credit card. You get energy quickly but you have to pay the bill, which means slowing down so the lactate can be reintegrated into normal aerobic metabolism and broken down to release usable energy. At altitude it takes longer to pay that bill. Recovery from hard effort takes longer and you often have to slow down more substantially than you would at sea level. You’ll get out of the saddle to accelerate at 10,000 feet and sooner than you expect you will be panting uncontrollably. You’ll sit back down and try to catch your breath, and it will feel like you’re going backwards. After one or two of those experiences you’ll learn to be more conservative with accelerations, pay attention your breathing, and gauge intensity by perceived exertion.

Off the bike you may experience a headache and disturbed sleep. The humidity is generally much lower at higher elevations, and you will lose more fluid to respiration and sweating. A headache is one of the first ways people new to altitude realize they are getting dehydrated. During your stay – on and off the bike – you will need to consume more water than you do at lower altitudes. If you normally drink caffeine, continue to do so. Alcohol will contribute to dehydration and headaches, so be conservative with your beer intake, at least until the final party!

Many people struggle to get to sleep or stay asleep at altitude, although this varies greatly from person to person. Staying hydrated can help, as can a humidifier in your room and avoiding alcohol. If you’re struggling to sleep through the night, be sure to focus on resting when you can during the day and night. An afternoon nap after finishing a stage can be very helpful. Also, make sure you get plenty of sleep before your trip to Colorado.

What you can do to prepare for altitude

The short answer is: Unless you have 3 weeks to spend at altitude, focus on maximizing your fitness. To truly acclimate to altitudes above 6,000 feet you would have to spend around 3 weeks at altitude to increase the oxygen-carrying capacity of your blood. Pikes Peak APEX competitors lead busy lives and have careers and families, so that’s most likely unrealistic. Sleeping in an altitude tent may work, but results are very individual. And in both scenarios, training quality and sleep quality can be negatively affected to such an extent that any improvement in oxygen-carrying capacity may be negated by lackluster training/recovery.

Here’s what you can and should do:

  1. Maximize your fitness. The altitude will diminish everyone’s performance to some extent. The better your fitness, the more power you will still have left after the altitude takes it down a notch. You will be able to cope with the effects of altitude better when you start out with better fitness, meaning you will recover more quickly from hard efforts and you will spend less time on the course and on major climbs (less exposure to the elements = more hours for recovery).
  2. Either arrive 5-7 days before the start, or the day before the start. Why not 2-4 days? Typically, athletes feel fatigued 2-3 days into their stay at altitude, and they feel and perform better starting about 4-5 days after arrival. If you don’t have enough time to spend a week before Pikes Peak APEX in Colorado Springs, your best alternative is to get there the day before the start. You may still experience fatigue after a few days, but you’ll start as fresh as possible.
  3. Pace yourself primarily by perceived exertion. Unless you already know how your body responds to altitude, it will be difficult to accurately pace your efforts–particularly on long climbs like those featured in the Pikes Peak APEX–based on power output or heart rate. Heart rate will be affected by altitude exposure, heat, hydration status, fatigue, and excitement. Sustainable power will diminish as you climb higher, but the extent of the decline is highly individual. You’ll want to monitor both power and heart rate, but in the moment, perceived exertion will be the most accurate gauge of intensity if you’re unaccustomed to or not acclimated to altitude.

What about altitude interventions?

Before you start investing time, energy, and money into things like altitude tents, altitude camps, or heat training for crossover acclimation, consider whether the potential gains are worth the potential cost. Unless you have already maxed out your VO2max and power at lactate threshold, and dialed in your recovery and nutritional strategies, you probably have more to gain from focusing on the fundamentals of training, recovery, and nutrition than you might gain from altitude interventions. This is particularly true because we know structured training, purposeful recovery, and focused nutrition work consistently, whereas altitude interventions could work if everything goes just right. The exception, in my view, is an altitude camp for the purpose of reconnaissance and experience. If you have the opportunity to spend a weekend riding at altitude before Pikes Peak Apex, whether in Colorado Springs to preview the courses or in some other part of the Rockies, take it. You’re not going to acclimate to altitude in such a short time, but you’ll learn what it feels like to ride at 6,000 to 10,000 feet above sea level and gain valuable information you can use later for pacing and gauging your efforts during the race.

One final note: The Pikes Peak APEX features an altitude range that is kind of a sweet spot for athletes from lower elevations. Yes, you’ll feel the altitude, but the majority of the racecourses are between 6,000 – 8,500 feet above sea level, with some shorter periods between 8,500 and 10,000 feet. And you’ll be sleeping at around 6,000 feet if you’re staying in Colorado Springs. This is more manageable than races in mountain towns like Breckenridge, Leadville, Vail, Aspen, and Snowmass, where the hotels and start lines are above 8,000 feet (or 10,200 for Leadville) and the races go up to 11,000-12,000 feet.