The atmospheric pressure is determined by the measure of the weight of a column of air directly over a spot. At sea level the weight and height of the column is greater than that of one at a higher altitude. Since the air is less dense, each liter of air contains less molecules of gas, the percentages still remain the same. However, since there is less of each molecule respectively there is less atmospheric or barometric pressure at higher altitudes. This decrease in partial pressure is directly related to the saturation of hemoglobin in the blood and therefore oxygen transportation throughout the cardiovascular system. Lower partial pressure of oxygen in the blood is termed hypoxia, while normoxia is the term given to describe the partial pressures at sea level. Since oxygen is only used in 2 out of the 3 energy systems, not all performances are altered at high altitude levels. Short term anaerobic exercises do not require oxygen, and therefore are typically not affected. Sprinters tend to have better times when racing in places of higher altitude due to the decreased air resistance.
The story is much different for aerobic exercise. At sea level, hemoglobin is about 96%-98% saturated with oxygen, versus 88%-71% at an altitude of 4,000 meters. Cardiovascular changes occur during the adaptation of training from sea level to a place of higher altitude. These changes include: lower maximal heart rate, decreased (sometimes increased) VO2 max, and increased pulmonary ventilation. Since the heart has a muscle that requires oxygen it operates at a lower heart rate due to the lack of oxygen concentration available in the blood. VO2 max is directly related to the capacity at which one can transport oxygen to the working muscles. It tends to decrease when exercising at a higher altitude because the amount oxygen available to transport between the blood and the muscles is decreased. Because of this the athletes “detrain” at higher altitudes because they are physically unable to get their heart rate up high enough to maintain their VO2 max. At 5,600 meters, the atmospheric pressure is one-half that of sea level and the number of oxygen molecules per liter of air is decreased by half; therefore a person’s pulmonary ventilation would have to double, sometimes causing fatigue in the diaphragm. Those with sickle cell trait and asthma would be more susceptible to having problems as opposed to an average person. A person with asthma would have a harder time catching their breath, due to the increase in pulmonary ventilation. A person with sickle cell trait is at increased risk because sickling of the red blood cells occur under extreme hypoxia (which can occur at high altitudes) resulting in obstruction of small blood vessels.
If all these changes occur, then why is the USA Olympic training center in Colorado Springs, one of the highest cities in the nation? Truth is, as your body adapts to the difference in barometric pressure, it will produce more red blood cells to compensate for the desaturation of hemoglobin. This adaptation can be very beneficial to someone who trains at a high altitude and competes at a lower altitude. Once the athlete returns to sea level they have an advantage over everyone else because they now have more red blood cells, meaning more oxygen, and oxygen transports equaling a higher VO2 max. The higher one’s VO2 max is, the more efficient their cardiovascular system is working, enabling it can last longer, thus improving aerobic performances. It appears as though the ones that are native to cities of higher altitudes have the ultimate advantage because studies prove that in order to have a complete adaptation one must spend the developmental years at high altitude.
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