The vertical limit is a term that describes the highest altitude the human body can survive which most agree is 18,000 feet above sea level. It is the point where normal, life sustaining functions such as breathing and blood circulation are affected by the lack of oxygen combined with low barometric pressure. Reaching the vertical limit does not prevent climbers from continuing to summit the world’s highest mountain peaks. It will, however slow their progress, requiring shorter steps, frequent rests and the aid of a portable supply of oxygen to complete their......

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