"High Altitude" seems to mean different things to different people. The Mount Everest base camp medical clinic defines high altitude as elevations between 4,921 feet (1,500 meters) and 11,483 feet (3,500 meters). Other organizations, including Princeton University's Outdoor Action program, have adopted what seems to be a more universal definition: 8,000 feet (2,438 meters) to 12,000 feet (3,658 meters). Elevations above 12,000 feet (3,658 meters) are considered "Very High" altitude, and elevations above 18,000 feet (5,500) meters are classified as "Extremely High."
To put that into perspective, the elevation of Denver, Colorado is one mile (5,280 feet, 1,609 meters) above sea level while Mount McKinley in Alaska claims the highest elevation in the United States at 20,320 feet (6,194) meters.
Our bodies undergo several common physiological changes at altitude. These include:
- Deeper and/or faster breathing
- Shortness of breath (especially during physical activity)
- Changes in nighttime breathing
- Increased urination
Symptoms of altitude stress include headaches, nausea, crabbiness and disrupted sleep. Though unpleasant, these are easily tolerated by most people at altitudes of up to 8,000 feet (2,438 meters). To avoid or ameliorate the effects of altitude, it's important to acclimatize yourself. We talk about that next.