This has been an interesting year with mountain bike, elite road, and masters road national championships being held at altitude. Throw in races like Ironman Tahoe, Ironman Boulder, Leadville 100, lots of XC mountain bike races, and events like the Death Ride and it is becoming very common for athletes to do at least one event a year at higher elevations. For those of us living at lower elevations, racing at higher elevation events can be very challenging. Not only do we see a decrease in aerobic capacity at elevation but pacing, nutrition, and hydration are all more complex at elevation. Estimating how altitude will affect you as an athlete as well as the metabolic changes are very important in an athlete’s race preparation.
Most of the research done on the effect of altitude in athletes was conducted before the 1968 Olympics in Mexico City (approx. elevation of 7400ft). The consensus from the studies concluded that an athlete loses 2% of VO2 for 1000ft above the first 1000ft. So what does that mean to actual performance? Bassett et. al. (1999) did a comparative analysis of cycling world hour records to put those loses of aerobic capacity into power terms for both acclimated and unacclimated athletes.
Bassett formula For acclimated athletes, in % of zero elevation power:
y = -1.12x^2 – 1.90x + 99.9 (R^2 = 0.973) where x=elevation in km
Instead of having to do all that math, here is an easy to read chart on the results from the Bassett study:
To put these into a real life example, if you were traveling to Truckee CA for Elite Road Nationals (~6000ft) a day before your event you would expect to experience a 11.1% drop in aerobic performance. However, if you were able to spend extra time at elevation and become acclimated your aerobic performance would only drop 7.3%. For an athlete with a sea level of threshold of 300 watts that is an almost 12 watt difference. While that may not seem like a lot, it can be huge when trying to make that breakaway stick or going up that final climb at the end of a long hot race.
The big question for a lot of athlete is how long does it take to acclimate? This where things become a little fuzzy. Several studies have been done on acclimatization all showing a pretty wide variance of individual responses. What we can conclude from these studies is that most athletes will need at least 2 weeks of altitude exposure and a maximum of 4 weeks to become complete adapted. This is assuming adequate iron and B vitamin stores. If either of those are low than adaptation to altitude will be slower and potentially incomplete. If you are targeting an event at elevation it may be useful to get a blood test done to ensure you have adequate serum ferritin, folate, and B12 levels.
Since most athletes can’t afford to spend up to a month at altitude before an event, we are seeing more and more athletes getting altitude tents to help with acclimatization. Altitude tents are essentially tents that go over an athlete’s bed and a device that lowers the oxygen content to create a hypoxic environment. This stimulates the lower oxygen absorption rate experienced at altitude and can help in the adaptation process, however in my experience the total time to be maximal adaptation from an altitude tent is about double the time needed at constant altitude exposure. Also, having optimal levels of iron and B vitamins is crucial in making this adaptation since the altitude tents primarily only alter hematological levels and don’t address the other physiological adaptations to altitude (breathing rates, reduced blood volumes, etc.). It is also because of this that we see slightly lower acclimatization rates from altitude tent use than full altitude exposure.
One important factor to keep in mind while spending time at altitude is that while your aerobic system is improving to the increased demands at altitude, muscular power will decrease due to the reduced workload. Essentially power, not heart rate, will be limited at altitude compared to what is possible at lower elevations and provide less stress to the muscles. Over time that can result in less anaerobic or sprint power. That is very important to take into consideration in that final preparation. If your event requires a lot of anaerobic power it may be important to include some trips to lower elevations to work on more powerful shorter duration efforts to maintain that ability.
Altitude not only affects aerobic capacity, it also can have a large affect on your fueling and hydration plan. For longer events like Ironman races, maximal VO2 is almost never a limiter. Instead we see metabolic fitness, how quickly and for how long can your body create energy, becomes a bigger limiter in athletic performance. There has only been a few studies on how metabolism is affected by altitude, but what has been done shows a shift to higher carbohydrate metabolism for any given work rate. This makes sense since relative intensity goes up as elevation increases at any given work rate.
The actual increase in carbohydrates varied by over 8 percent, but typical results showed an average 20% more carbohydrate utilization at 7500ft compared to 2500ft. The larger and more fit the athlete resulted in a bigger metabolic effect on athletes. Smaller, less fit athletes are less metabolically affected. Just as with aerobic function, becoming acclimatized to the higher altitudes will also affect the metabolic shift.
This metabolic shift in carbohydrate oxidation is very important for 70.3 and Ironman athletes. Just as it is important to adjust a long course athlete’s pacing strategy to account for reduced aerobic capacity, it may also be important to reduce intensity to spare carbohydrate stores. Beyond acclimatizing to the higher elevation, working on becoming more metabolically efficient may also have a huge impact on performance. Through a combination of diet manipulation and specific training it is possible for athletes to increase the amount of fat they burn at any given intensity. This is a pretty complex topic and something I will cover in a separate article in the near future.
Hydration also becomes a bit more difficult at altitude since the absolute humidity decreases as you go up in elevation. It isn’t uncommon to see absolute humidity in the mid to low 30% range which would increase fluid loss through respiration and may increase sweat rate. One of the biggest preventable issues I see with athletes competing and training at altitude is dehydration. Nothing will slow you down faster than becoming dehydrated and it is a huge risk at higher elevations. It isn’t uncommon for endurance athletes to go through 20 – 32 ounces of fluid an hour at altitude. That is 2 big bike bottles for every hour of exercise! With that much fluid it is important to pay attention to electrolyte content as well to avoid becoming hyponatremic. I would recommend using a product like Salt Stick tabs, or Skratch Hyper Hydration to maintain sodium levels with the increase fluid intake. It is also important that you maintain hydration outside of your sport as well. I recommend that all athletes start the day with 16oz of water with electrolytes (salt stick tabs, Nuun, 1/4tsp good quality sea salt, or trace minerals) and never go anywhere without a water bottle when at elevation.
Since there is quite a bit of individual variance in responses to altitude it is important for athletes to work out their individualized plan. Of course if you have the time spending 2 – 4 weeks at your favorite mountain resort is by far the best option, just not very practical for most of us. Another useful strategy is to minimize altitude exposure leading up to an event and going up as late as possible before an event. While this doesn’t help to become physiologically adapted, it does limit some of the short-term negative effects of altitude. It is common to see performance decline rather rapidly the first few days at elevation, then it slowly starts to come back up as the body becomes adapted. Going up the day before or day of an event can limit the initial decline in performance and be a better plan than going up 2 – 4 days before an event.
However you approach events at altitude, make sure you make a plan and address the unique demands of these events. Some of my best racing experiences have occurred over 5000ft and I wouldn’t of enjoyed them as much without addressing the unique demands of performing at altitude. Maybe it is time for you to join the athletic mile high club…