For many endurance athletes, at some point we will train and/or race at high altitudes. However, what are the actual effects of altitude on our performance and our physiology? Typically, the negative effects of altitude on performance are seen around the 5,000-foot mark (1). Acutely (i.e., in the short-term), altitude causes a decrease in performance due to a lower partial pressure of oxygen in the surrounding air. This does not mean that there is LESS oxygen in the air. The composition of air remains steady at ~21% oxygen, however, there is a lower pressure of oxygen due to the oxygen molecules being more spread out. This essentially means that less oxygen gets into your system, and this subsequently causes an immediate reduction in an athletes VO2 Max, anaerobic/lactate threshold, and a higher perceived exertion and heart rate at all intensity/effort levels than compared to lower elevations. How much of an impact does altitude have on performance? Well, typically performance declines by ~1-2% for every 1,000 feet in altitude an athlete travels upwards (https://www.trainingpeaks.com/blog/the-effect-of-racing-at-altitude). For example, if a cyclist has a max aerobic power output (i.e., VO2 Max) of 400 watts at sea level, then that power output might be somewhere around 360 watts at 5,000 feet! You can see how this might begin to affect one’s ability to train and race at altitude when compared to sea level.
How does acclimating/acclimatizing to altitude work?
For those of us not living at higher altitudes like in Flagstaff, AZ (~7,000 feet) or Boulder, CO (~5,000 feet), a little more care and attention must be utilized when attempting to train and race at higher altitudes. For those that are in fact living at high altitude, going down to train and race at sea level will place them at an advantage naturally because of the physiological adaptations they have over us sea-level or low altitude dwellers. Chronic (i.e., long-term) exposure to altitude causes an increase in the number of red blood cells that are in our blood stream, ultimately improving our performance to help off-set the negative effects of altitude (1). These benefits are not realized while still living at high altitude, but are seen when travelling down to lower altitudes as these physiological adaptations remain for up to 3-4 weeks after being exposed to altitude (1). The higher red blood cell count will improve VO2 Max, anaerobic/lactate threshold, and the ability to train at all effort levels with a lower heart rate. This means you will be able to train and race faster!
Now, how long does it take to see these physiological changes that enhance performance? Unfortunately for those of us who don’t LIVE at naturally high altitudes above ~4,000-5,000 feet, research demonstrates that ~3-4 weeks of exposure to altitudes of at least 5,000 feet is needed to allow the body enough time to adapt through an increase in red blood cells (1). Exposure to altitude for a few days or even a full week likely yields no benefit on performance, and only hinders training and racing performance while staying at higher altitudes.
I know most of us that aren’t full-time professional athletes will not have the flexibility in our lives to be able to stay at altitude for 3-4 weeks. To make matters even more difficult for us to access the benefits of altitude exposure, the most well-documented approach to altitude exposure is to live high and train low. This is accomplished by sleeping and living at high altitude and then travelling down to lower altitudes to perform key or intense training sessions so that higher altitudes does not compromise the ability of the athlete to perform faster and higher-intensity efforts. This maximizes the benefits of altitude exposure while allow the athlete to still hit their paces during key sessions. A perfect example of this is the Northern Arizona Elite running group that lives in Flagstaff, Arizona. They have the ideal setup as they all typically live in Flagstaff, Arizona at ~7,000 feet of elevation and then, for key race-pace sessions or for very intense sessions, they will drive down to lower altitudes (~3,000-4,000) feet that are only an hour away. This set up allows them to maximize their adaptations to altitude AND to training.
How to approach altitude for training and racing?
For those living at higher altitudes year-round, your solution to this all is simple. Training and racing at your usual high altitude will occur as usual without any impairment on performance as you are fully adapted to that altitude. Going up even higher to train and race would confer an impairment on you performance, at which time you would want to follow the guidelines I outline for low-altitude dwellers below. When racing at lower altitudes, you are at an advantage to everyone else as you carry around a higher red blood cell mass than if you lived at lower elevations. It’s like a legal form of EPO!
For those of us living at sea level or lower altitudes, here are some evidence-based guidelines when approaching training at altitude:
1. DON’T travel to altitude for a day, a few days, or even a week and expect it to improve your performance. It will only hurt your performance while training at altitude.
2. If you are going up to higher altitudes to train, expect that your effort level will need to be reduced across all exercise intensities to maintain the integrity of your training sessions. For example, a zone 1 recovery run will likely need to be done at a lower pace than at your usual living altitude. I would recommend you use heart rate zones to guide easy and aerobic training sessions to make sure you keep them truly easy or aerobic. For intense training sessions in zone 4 or zone 5, keep in mind you likely won’t hit your usual paces or power outputs at your normal living altitude, and so the physiological stimulus garnered from these sessions won’t be quite as intense as it would be at lower elevations.
3. Know that it takes 12-14 hours per day of altitude exposure at at least 5,000 feet for 3-4 weeks to see improvements in performance at lower elevations.
4. When training at higher altitudes, be sure to drink more than usual and to bump up your carbohydrate intake during training as higher altitudes lead to greater fluid losses (due to higher than usual respiration rate and usually drier conditions) and a greater preference for carbohydrate metabolism during training.
5. If you are staying at altitude for extended periods of time to fully acclimatize, know that you may require an iron supplement as research tends to show that supplemental iron is needed to maximize the physiological adaptations conferred from living at altitude (1).
For those of us living at sea level or lower altitudes, here are some evidence-based guidelines when approaching racing at altitude:
1. If you are planning on acclimatizing to altitude before you race, try giving yourself at least 5-6 days of exposure to the racing altitude beforehand to begin to see a benefit as research tends to point towards six days as being the absolute minimum number of days needed to start to acclimatize (2). There will still be a negative effect of altitude on your performance, but it may be very slightly less than if you were NOT to acclimatize. Also, some people tend to feel sick (i.e., altitude sickness) during the first few days of living at higher altitudes, and so giving yourself nearly a week of exposure should at least get rid of that sensation, which should help you perform better. Also, see the TrainingPeaks article I mentioned above as they include a table with the expected % reductions in capacity that you could use to help predict more appropriate target paces and power outputs for your race.
2. As with training at altitude, be sure to up your fluid and carbohydrate intake from your usual intake at your normal living altitude as your needs will be higher. This is particularly important for races lasting longer than 90 minutes as fluid intake and energy intake become more important factors predicting performance.
There you have it! A one-stop-shop guide for you when approaching altitude! Whether training or racing at altitude, it is important that you understand the effects of altitude as well as how to approach acclimatization to altitude. Research is mounting on this topic as it is of great importance to training and racing. Be smart with your use of altitude for training, and plan ahead to make sure you perform your best if racing at altitude.
Finally, this isn’t the first time I have written a piece on altitude. To read more on this topic, you can click here to read a post I published in May of 2019. In this piece, I cover a specific research study that aimed to investigate the effects of various 2-day exposure techniques before subsequent run time-trial performance at high altitude in order to see if there was an approach that would help reduce the negative impact of altitude on performance.
1.Saunders PU, Garvican-Lewis LA, Chapman RF, Périard JD. Special environments: Altitude and heat. International journal of sport nutrition and exercise metabolism. 2019 Mar 1;29(2):210-9.
2.Kenefick RW, Beidleman BA, Andrew SP, Cadarette BS, Muza SR, Fulco CS. Two-Day Residence at 2500 m to 4300 m Does Not Affect Subsequent Exercise Performance at 4300 m. Medicine and science in sports and exercise. 2019 Apr;51(4):744-50.
Happy training and racing!
-Ryan Eckert, MS, CSCS
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