USA Pro Cycling Challenge: Altitude Test Lab – 2

Information about altitude on the internet varies from highly scientific to relatively straightforward. My goal is to present a condensed (no pun intended) description of why and how high altitude has an effect on athletic performance and then draw conclusions about what this all means for the USA Pro Cycling Challenge (UPCC) in Colorado. Jump to the bottom for these conclusions.

What is different at altitude?

The root of physiological and resulting performance impacts at higher altitude is this: higher elevation equates to lower pressure. The air’s barometric pressure and the partial pressure of oxygen both decrease as elevation increases. Folks refer to air at higher elevations as “thinner;” while the percent of oxygen in the air is 21% at any level, the number of molecules is lower at lower pressure in a given volume. There is less oxygen in total available to breathe. According to Matt Fitzgerald writing for Competitor, “at 8,000 feet the barometric pressure is twenty-five percent lower than it is at sea level—meaning you get 25 percent less oxygen per breath than you get at sea level.”

Partial pressure is the pressure a gas (eg, oxygen) in a mixed gas environment would have if it were the only gas present. Oxygen’s partial pressure lowers as elevation rises, which means less oxygen is able to pass from the lungs to the blood and tissues to fuel muscles. These numbers from sport fitness advisor demonstrate the effect of elevation on oxygen’s partial pressure: “At sea level, oxygen has a partial pressure of 159mmHg.  In Mexico City [7,350 foot elevation] it is approximately 125mmHg.  At the top of Everest, it drops to 48mmHg, which is nearly equal to the [pressure of] blood surrounding the lungs.”

How does the body respond?

Here’s a good summary from roadcycling.com, with some additions.

The body’s initial response to altitude is to increase breathing rate to consume the same amount of oxygen as at sea level, and to increase heart rate at both rest and during submaximal exercise. In addition, blood is concentrated by reducing the fluid or plasma component; reducing this watery part of the blood has the effect of increasing red blood cell density. “Collectively, these changes improve oxygen uptake by the lungs and its delivery to tissues. The disadvantages of these changes are that perceived exertion at any workload is increased and circulating blood volume is reduced.”

How is performance affected?

Trail Runner Mag.com sums it up well: “the amount of work you can do is less.”

Some detail from sport fitness advisor on decreased maximal cardiac output: “During exhaustive exercise at maximum levels both maximal stroke volume and maximal heart rate decrease with altitude. This obviously combines to have a significant effect on maximal cardiac output.  In conjunction with the reduced diffusion gradient to drive oxygen from the blood to working tissues, it is easy to see why VO2 max and endurance performance is hindered…Maximal oxygen uptake begins to decrease significantly above an altitude of 1600m (5249ft).  For every 1000m (3281ft) above that VO2 max drops by approximately 8-11%.”

Can the physiological changes due to altitude be “fixed?”

Yes, partially, and it depends on length of stay at altitude to acclimatize and the elevation at which an athlete competes. While the sources I consulted varied a bit in their timeframe conclusions, these excerpts offer a framework to start from.

From cyclingperformancetips: “An increase in the blood hemoglobin (hematocrit) level over 3 to 4 weeks increases the oxygen carrying capacity of  the blood and is the most important of all the performance adaptations to altitude.” There are cellular changes as well. “The capillary concentration in skeletal muscle is increased in animals living at altitude compared to those at sea level, and muscle biopsies in acclimatized men have shown an increase in myoglobin, mitochondria, and the metabolic enzymes necessary for aerobic energy production. Taken together, these changes improve the efficiency of oxygen delivery to the muscle cell as well as the extraction of blood oxygen at the muscle cell level. These adaptations are sufficient to restore maximum aerobic exercise capacity (VO2max) to NEAR sea level values at altitudes up to 2500 meters (7500 feet). At higher elevations, acclimatization will never restore VO2 max. to what is possible at sea level.”

Riders in the UPCC will compete above 7,500 feet on nearly all of the stages.

Matt Fitzgerald offers two suggestions athletes can consider aside from spending time at altitude. Both of these are supported by research studies on cycling time trial performance: green tea extract which counteracts increased production of free radicals by working muscles at altitude, and  0.2 to 0.4 gram of baking soda (sodium bicarbonate) per kilogram of bodyweight before exercise to buffer increased blood acidity from increased respiration. On the latter, Matt adds: “Be aware, however, that possible side effects include nausea, vomiting, and diarrhea.”

If supplemental oxygen is allowed during competition, there’s always the Oxygen Lounge Oxygen Bar in Breckenridge as well as door-to-door oxygen delivery.

What might we expect to see in the UPCC as a result?

• Fewer attacks. Levi referred to a single speed in his quote in Part 1. If the guys are unsure about how to dose their efforts, we might see less attacking on the climbs.
• A very fast sprint into Steamboat Springs. According to at least one study, moderate altitude “is likely to enhance cycling performance on flat terrain because the benefit of reduced aerodynamic drag outweighs the decrease in maximum aerobic power [maximal oxygen uptake (O)].”
• Wins from those living and training at altitude, or arriving very early to acclimatize. It’s hard to tell if the physiological benefit advantage is significant enough given all the other factors that need to align to win a race, but at a minimum increased familiarity with how high altitude feels should be helpful.
• Surprise winners. It’s also hard to know if the riders in the UPCC will respond in a similar fashion to the athletes studied in the articles I reviewed. Could there be a rider whose body chemistry would allow him to thrive when others suffer?
• Guarding recovery time. Those serious about the race may be less available publically as they maximize opportunities for recovery.

I’m anxious to see how this altitude test lab of a race turns out. Hope to see you at one of the stages.

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Sources for this article:

http://www.roadcycling.com/training/Altitude_Training_for_Improved_Cycling_Performance_002474.shtml

http://www.sport-fitness-advisor.com/acclimatization-to-altitude.html

http://www.cptips.com/altitud.htm

http://running.competitor.com/2011/05/training/racing-at-high-altitude_28105

http://www.ingentaconnect.com/content/adis/smd/2001/00000031/00000007/art00008