How does altitude affect your training?
November 4, 2025
Last month, some friends and I climbed Mt. Whitney*. Of course, the greatest challenge of Whitney is the altitude, peaking at 14,505 ft. After a successful summit, a friend and I wondered: Are there potentially negative effects on running from being at altitude? We knew we hadn’t been at altitude long enough for the known aerobic benefit, but we were more fatigued than we expected to be in the following days. Was it coming from something specific? I did some searching to find out.
A quick altitude rundown
“Altitude” is anything over 5,000 feet above sea level, but typically pros training at elevation aim for 7,000-9,000 feet. Runners must altitude train for at least 3-4 days, but they get the most benefit staying for 3-4 weeks.
Why altitude train?
The main benefit is improving your body’s ability to send oxygen to your muscles. There is less oxygen at altitude, and the amount decreases the higher you go. At 8,000 feet, there is a quarter less oxygen in the air than at sea level. To compensate for this when training at altitude, the body churns out more oxygen-carrying red blood cells (RBC’s). These little dudes carry extra oxygen to muscles — aka, improving the runner’s infamous VO2 max.
This increased number of RBC’s lasts a few weeks after the runner returns to sea level. Here, they benefit from having more oxygen-carrying RBC’s than normal in an already oxygen-rich environment. Most athletes will notice their running performance improved from before going to altitude.
What are the concerns with altitude training?
For one, altitude sickness is always possible. Typically, this consists of a headache and maybe some nausea or extra fatigue that subsides once a person goes to lower elevations. However, the effects can sometimes last for hours or even a day or two.
Altitude training is also dehydrating. People breathe faster at higher elevations, so they lose water through respiration more quickly. The air at altitude is also simply drier (don’t forget your chapstick).
Perhaps most relevant for runners, making more RBC’s involves increasing the protein hemoglobin, which requires healthy iron levels. Many runners, especially ones who menstruate, have low iron, so altitude training can feel harder and be less effective for these folks.
Lastly, as typical with activities that cause physical stress, altitude training can weaken one’s immune system and ability to recover from tough workouts. Usually, runners reduce training volume and intensity when first going to altitude to avoid this.
The bottomline
Running at altitude can improve performance if you have proper recovery, nutrition, and smart training.
For my friend and I, we experienced increased fatigue simply from having a physically challenging weekend with little recovery (and probably low iron, to be honest). No mysterious altitude effects involved. Turns out we’re just not invincible (yet). This isn’t surprising, but it’s still a great excuse to book a longer trip to the mountains next time.
*Some others cycled from Death Valley’s Badwater Basin to the Whitney Portal — and one did both of these activities! While that is insanely impressive, today we’re focusing on altitude.