At altitude, the reduction in oxygen available has the most predominant impact on the stage racer’s performance. There are both direct and indirect effects at work here however they all make racing more difficult. While the mechanisms associated with all these effects may be complicated, we can boil them down into some very understandable concepts.
Lack of oxygen:
While the percentage of oxygen in air is the same (21%) no matter what the altitude is, the amount of oxygen in a constant volume of air decreases as the altitude increases. Think of it this way; compared to sea level each breath at altitude has less oxygen in it. If there is less oxygen in each breath, then less oxygen is available for (and transferred to) your body for use in metabolism. Metabolism is how your body produces energy to function and race.
As you can see in the chart below the amount of oxygen available at what we are defining as high altitude (5,000 ft and above) is 17% less than at sea level and drops off even further the higher you go!
|Altitude||% O2 compared to Sea Level|
So, when you have less oxygen available than what you are typically accustom to you can develop what is known as hypoxia. This is especially true when exerting yourself. A hypoxic response is triggered by various changes in your bloodstream and your body reacts to counter this lack of oxygen. Holding your breath for an extended time triggers a prompt hypoxic response.
Some of these reactive measures are immediate (increased respiration) others are more long term such as the production of more red blood cells which carry oxygen throughout your body. Either way you body starts to react to the lack of oxygen. If it is temporary (as in an anaerobic push) then once sufficient oxygen is again available the hypoxic response tapers off. If it is long term then your body continues to adjust. This latter case is the one we are more concerned with when racing at altitude.
Your body adjusting to prolonged lower oxygen availability is more commonly known as acclimatization. Some people acclimatize very rapidly, others do not. Still there are a few out there that can not fully acclimatize to high altitudes. Much of this is genetic so you can thank or curse your ancestors. Your level of physical fitness can help but it does not guarantee the ability to acclimatize. In fact, there are extremely fit individuals out there that find it impossible to acclimatize to high altitudes especially over 10,000 ft (3,050 m).
Impacts on Stage Racing:
Stage racing is such a unique sport. More than an ultra, it requires maintenance of one self over an entire week. Therefore acclimatization plays a critical role to the stage racer. The understanding of altitude effects and the ability to manage them makes or breaks it during a stage race since you just can not “gut it out” for 24-36 hrs. Understanding what is in store and how to deal with it is important since there are many factors to consider.
Some Things to Expect:
- Decreased Performance: The extent to which you can do hard aerobic work is determined by the maximum rate at which your body can take up oxygen. With the reduced oxygen availability at altitude your capacity for oxygen consumption drops. There is little improvement even with acclimatization. Sorry, that is just how it is so mentally be prepared for this.
- Increased rate of breathing: You need more oxygen so you breath faster (and deeper).
- Increased heart rates: You will be striving to move limited oxygen throughout your body and thus your heart rate will increase even at rest.
- Dehydration: With increased respiratory rates you will expire more water and thus become dehydrated quicker. Additionally at higher altitudes the air is colder and more dry.
- Brain fatigue: With less oxygen available you can experience a loss of mental sharpness
- Insomnia/restless sleep: This is very common. It is also has a huge impact on the stage racer since sleep/rest/recovery are so important. During sleep your respiration slows down and thus so does oxygen availability to your body. At some point you may slip into a hypoxic situation and you will involuntarily wake up. This is somewhat analogs to sleep apnea. No good sleep, no good recovery.
Some Things you Might See:
Many of the following can be symptoms of Acute Mountain Sickness (AMS) which can impact individuals who have not acclimatized sufficiently. Typically symptoms of AMS appear within 12-24 hours of arriving at altitude however they will typically be gone in about three days as the body acclimatizes. If they persist then moving to a lower elevation is needed as well as potential medical intervention.
- Loss of appetite
- Dizziness and nausea
- Impaired thinking
All of the above can spiral out of control rapidly and result in a DNF. Since these symptoms occur early in the acclimatization process they may be occurring during the early stages of a race.
Other Things to Watch out for:
Finally, you should also keep an eye on the following when at altitude since they can impact your race.
- Sun: At higher altitudes ultra violet rays are more intense. Sunburns can easily occur.
- Weather: Weather can rapidly change up high. One minute it can be sunny and fair, the next there can be rain, snow, lightning, wind, etc. Be ready for it.
- Hallucinations: Some may experience more frequent or more intense hallucinations at very high altitudes during prolonged periods of sleep deprivation (as during a long stage).
All this sounds like bad news. But fear not! You can prepare yourself to minimize these potential effects and maximize your racing performance. Next up is Training and Acclimatization.