The Earth is composed of more than 100 elements, the most abundant of which is oxygen. Oxygen is essential to the survival of all living matter. We can live without food for weeks and without water for days, but take away our supply of oxygen for just 4 minutes and death is almost assured.
For athletes a lack of oxygen will severely hamper performance by causing an increase in lactic acid in the muscles and a loss of energy. Without sufficient oxygen, your muscles will reduce glucose into lactate and release hydrogen ions into the muscles, leading to pain, cramps, and fatigue.