On your first day at altitude, you go for a run, and notice within a few steps that you’re breathing heavier than usual. You wonder why, because the air still contains 20.93% oxygen, whether you’re at the Dead Sea in Israel (1,385 feet below sea level) or on top of Mount Everest in Nepal (29,029 feet above sea level).
The defining characteristic of altitude is a lower barometric pressure, which keeps decreasing the higher up you go. That reduces the partial pressure of oxygen in the air, resulting in less oxygen entering your lungs each breath. To compensate, you breathe more to inhale more oxygen.
Running at altitude stimulates the production of red blood cells (erythropoiesis, named after erythropoietin, the hormone that stimulates red blood cell production) as part of acclimatization, giving your blood a greater oxygen-carrying capability when you return to sea level.
The ideal altitude to train at is 6,500 to 8,000 feet for at least 4 weeks to obtain the greatest erythropoietic benefit and giving you enough time to get past any symptoms of acute mountain sickness.
Since your VO2max is lower at altitude above 3,400 feet, adjust your pace to make your workouts physiologically equivalent to sea-level workouts. VO2max decreases by about 2.6% for every 1,000 feet of altitude above 3,400 feet. How to calculate running speeds for altitude workouts:
# of feet at altitude – 3,400 feet = A
(A x 0.026) ÷ 1,000 feet = B
B x sea-level pace in minutes = C
C + sea-level pace in minutes = new altitude pace in minutes
Then, convert the decimal from the new altitude pace into seconds by multiplying the decimal by 60 to get your new altitude pace. For example, at an altitude of 5,000 feet and a sea-level pace of 7:00 per mile:
5,000 feet – 3,400 feet = 1,600 feet
(1,600 x 0.026) ÷ 1,000 feet = 0.0416
0.0416 x 7.0 minutes = 0.2912
0.2912 + 7.0 minutes = 7.2912 minutes
0.2912 x 60 = 17 seconds = 7:17 per mile pace
For more info, check out my new book, Running Periodization: Training Theories to Run Faster.