Running at High Elevation: Definition, Physiological Effects, and Acclimatization

What is a High Elevation for Running?

A "high elevation" for running generally refers to altitudes above 1,500 meters (approximately 5,000 feet) where the atmospheric pressure and, consequently, the partial pressure of oxygen in the air significantly decrease, leading to noticeable physiological challenges for the human body.

Defining High Elevation for Physiological Impact

While any ascent above sea level introduces some change, specific thresholds are recognized for their impact on human physiology, particularly for physical exertion like running.

• Low Altitude: Sea level to 1,500 meters (approx. 0-5,000 feet). Most people experience minimal to no noticeable physiological effects during exercise.
• Moderate Altitude: 1,500 to 2,500 meters (approx. 5,000-8,000 feet). At this range, some individuals may begin to experience mild symptoms of altitude sickness, and exercise performance is measurably impaired. Runners will typically notice increased breathlessness and difficulty maintaining their usual pace.
• High Altitude: 2,500 to 3,500 meters (approx. 8,000-11,500 feet). This is where the term "high elevation" most accurately applies to significant physiological challenges for running. Performance is substantially reduced, and the risk of acute mountain sickness (AMS) increases.
• Very High Altitude: 3,500 to 5,500 meters (approx. 11,500-18,000 feet). Sustained activity is very difficult, and the risk of severe altitude sickness (HACE, HAPE) is significant.
• Extreme Altitude: Above 5,500 meters (approx. 18,000 feet). Human habitation is not sustainable long-term, and survival requires extreme acclimatization and specialized equipment.

For runners, the critical threshold where "high elevation" becomes a significant factor in performance and physiological response typically starts around 1,500 meters (5,000 feet), with effects becoming more pronounced above 2,500 meters (8,000 feet).

Physiological Responses to High Elevation

The primary challenge at high elevation is hypoxia, a condition of reduced oxygen availability to the body's tissues. This is not due to a lower percentage of oxygen in the air (which remains ~21%), but rather a lower partial pressure of oxygen due to decreased atmospheric pressure.

When a runner ascends to high elevation, the body initiates several acute and chronic adaptations:

• Increased Ventilation (Breathing Rate and Depth): The body immediately increases how much air it moves in and out of the lungs to try and compensate for the reduced oxygen. This leads to the sensation of being more out of breath even at rest.
• Increased Heart Rate: To deliver sufficient oxygen to working muscles, the heart beats faster and pumps more blood per minute. This elevates the cardiac output.
• Fluid Shifts: There can be initial shifts in body fluids, potentially leading to dehydration if not managed.
• Changes in Blood Chemistry:
  • The kidneys produce more erythropoietin (EPO), a hormone that stimulates the production of red blood cells. This is a slower, chronic adaptation that increases the blood's oxygen-carrying capacity.
  • Changes in blood pH occur due to increased ventilation, which can affect oxygen binding to hemoglobin.
• Metabolic Adjustments: The body may shift its fuel utilization patterns, potentially relying more on carbohydrates and becoming less efficient at utilizing fats.

These adaptations aim to improve oxygen delivery and utilization, but they come at a cost, primarily reduced aerobic capacity and increased physiological strain during exercise.

Acute Mountain Sickness (AMS) and Its Relevance to Runners

Runners, especially those who ascend rapidly or exert themselves intensely before acclimatization, are susceptible to AMS. This is the most common form of altitude sickness and is generally mild, but can progress if ignored.

Common symptoms of AMS include:

• Headache: Often the first and most prominent symptom.
• Nausea or Vomiting: Digestive upset.
• Dizziness or Lightheadedness: Feeling unsteady.
• Fatigue or Weakness: Unexplained tiredness disproportionate to effort.
• Difficulty Sleeping: Disturbed sleep patterns (periodic breathing).

These symptoms typically appear 6-12 hours after arrival at elevation and usually resolve within 24-72 hours with proper acclimatization. For runners, pushing through these symptoms can be dangerous and hinder proper acclimatization.

Acclimatization Strategies for Runners

Acclimatization is the process by which the body adjusts to the lower oxygen levels at high elevation. For runners planning to run or race at altitude, proper acclimatization is crucial for performance and safety.

Key strategies include:

• Gradual Ascent: If possible, ascend slowly, spending a night or two at intermediate elevations before reaching the final destination.
• Rest and Reduce Activity: For the first 24-48 hours at high elevation, significantly reduce running intensity and duration. Focus on light activity and rest.
• Stay Hydrated: Drink plenty of fluids (water, electrolyte drinks). Dehydration can worsen AMS symptoms.
• Nutrient-Rich Diet: Consume a balanced diet, perhaps slightly higher in carbohydrates. Avoid excessive alcohol and caffeine, especially initially.
• Listen to Your Body: Pay close attention to any symptoms of AMS. If symptoms worsen, descend to a lower elevation.
• Medication (Consult Physician): In some cases, a physician might prescribe medications like Acetazolamide (Diamox) to aid acclimatization, particularly for rapid ascents or those with a history of AMS.

Training at Altitude: Benefits and Considerations

Training at high elevation is a common strategy for elite endurance athletes, aiming to elicit physiological adaptations that improve performance at lower altitudes.

• "Live High, Train Low" (LHTL): This popular approach involves living at high elevation to stimulate red blood cell production and other adaptations, but descending to lower elevations for high-intensity training sessions. This allows athletes to maintain training intensity, which is difficult at altitude, while still gaining the benefits of living in a hypoxic environment.
• "Live High, Train High" (LHTH): This involves both living and training at high elevation. While it promotes strong acclimatization, the inability to maintain high-intensity training can lead to detraining effects for certain physiological systems.

Potential benefits of altitude training for runners include:

• Increased Red Blood Cell Mass: Leading to enhanced oxygen-carrying capacity.
• Improved Oxygen Utilization: Cellular adaptations within muscles for more efficient oxygen use.
• Enhanced Buffering Capacity: Better ability to manage metabolic byproducts during intense exercise.
• Improved Running Economy: Some studies suggest improvements in the energy cost of running.

However, training at high elevation also carries considerations:

• Reduced Training Intensity: It's difficult to maintain the same pace and power output at altitude, which can be frustrating and may lead to a decrease in certain fitness parameters if not managed carefully.
• Increased Recovery Needs: The body works harder to adapt, requiring more rest and recovery.
• Risk of Overtraining: Pushing too hard too soon can lead to overtraining syndrome.
• Individual Variability: Response to altitude training varies greatly among individuals.

Practical Advice for Runners at Elevation

• Pre-Acclimatization: If possible, arrive at high elevation several days to a week before a race or intense training block. For very high altitudes, even longer may be necessary.
• Adjust Expectations: Your running pace will be slower, and your perceived effort will be higher for the same pace. Do not try to maintain your sea-level pace.
• Pace Yourself: Start runs significantly slower than usual. Focus on effort rather than pace.
• Hydrate Diligently: The dry air and increased respiration at altitude lead to greater fluid loss.
• Monitor Symptoms: Be vigilant for signs of AMS. If symptoms develop, cease activity and rest.
• Nutrient Timing: Ensure adequate caloric intake, particularly carbohydrates, to fuel your runs and aid recovery.

When to Seek Medical Advice

While mild AMS often resolves with rest and descent, certain symptoms warrant immediate medical attention:

• Worsening Headache: That isn't relieved by over-the-counter pain relievers.
• Severe Nausea/Vomiting: Inability to keep food or water down.
• Significant Dizziness/Loss of Balance: Inability to walk in a straight line (ataxia).
• Shortness of Breath at Rest: Or a persistent cough, especially if producing frothy sputum.
• Confusion or Altered Mental Status:
• Blue Lips or Fingernails (Cyanosis):

These could be signs of more severe, life-threatening forms of altitude sickness, such as High Altitude Cerebral Edema (HACE) or High Altitude Pulmonary Edema (HAPE), which require immediate descent and medical intervention. Always prioritize safety over training or racing goals at elevation.