Today we are going to discuss everything altitude. More specifically the physiological changes that occur in the body, the acute and chronic adaptations, and how long it takes to become altitude adapted. Let's dive right in.

Acute Adaptations To Altitude

When elevation exceeds 3900 feet acute changes begin to occur in the body to make up for the reduced partial pressure of O2 in the atmosphere. The two changes that happen early in the acclimatization process are increased hyperventilation at rest and during exercise and increased cardiac output at rest and during submaximal exercise.

The increase in hyperventilation is due to increased breathing frequency. With longer stays at high altitude, however, increases in tidal volume also causes increased ventilation. Ventilation stabilization depends on the level of elevation.

Regarding cardiac output increasing during the early stages of altitude adaptation, sub max heart rate and cardiac output can increase by 30-50% above values seen at sea level, while SV (stroke volume) is constant or minimally decreased. The increase in submaximal cardiac output is due to the need for increased blood flow when oxygen in the blood is decreased.

Chronic Adaptations To Altitude

After 10 to 14 days at altitude, cardiac output and heart rate start to return to normal levels due to increased red blood cell production. It follows that with acute exposure to elevation, increased ventilation and sub-max cardiac output occur quickly and are effective to offset the difficulty of the decreased partial pressure of O2. Despite these adjustments, blood O2 decreases and causes decreases in max O2 uptake and endurance performance. These changes that occur return to normal after about 1 month when returning to sea level.

In sum, the chronic metabolic and physiological changes that occur during prolonged altitude exposure include:

• Increased hemoglobin (5-15%) and red blood cells (30-50%).
• More efficient diffusion of O2 through pulmonary membranes.
• Increased capillary formation.
• Maintenance of acid-base balance of body fluids through excretion of bicarbonate and through hyperventilation.

All these changes can lead to increases in VO2 max and improved performance upon return to sea level. Additionally, these adaptations can improve tolerance to endurance exercise at medium and high altitudes and could result in near sea level performances with appropriate acclimization.

How Long You Should Stay At Altitude

It is generally recommended that an endurance athlete needs a minimum of 3 to 6 weeks at altitude to realize any adaptations and improvements in performance upon return to sea level. However, it should be noted that long-term exposure to altitude can result in reduced performance.

The following table lists the immediate and long-term adjustments to altitude training: