Altitude Acclimation 3
You can see there is a steady decrease in inspired, or inhaled, oxygen as you gain elevation. Remember that room air at sea level is 21% oxygen, hence the highest percent of fractional inspired oxygen you can have is 21% (1).
Bryon Powell is the Editor-in-Chief of iRunFar. He’s been writing about trail running, ultrarunning, and running gear for 15 years. Aside from iRunFar, he’s authored the books Relentless Forward Progress: A Guide to Running Ultramarathons and Where the Road Ends: A Guide to Trail Running, been a contributing editor at Trail Runner magazine, written for publications including Outside, Sierra, and Running Times, and coached ultrarunners of all abilities. Based in Silverton, Colorado, Bryon is an avid trail runner and ultrarunner who competes in events from the Hardrock 100 Mile just out his front door to races long and short around the world, that is, when he’s not fly fishing or tending to his garden.
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