12.1 Exercise at altitude

Exercise at altitude presents unique challenges for the human body. Reduced oxygen availability triggers physiological responses like increased ventilation and heart rate, while also decreasing exercise capacity. These changes can lead to acute mountain sickness and impaired performance.

Acclimatization helps the body adapt to high-altitude environments. Over time, respiratory and cardiovascular systems adjust, improving oxygen delivery and utilization. However, performance at altitude remains compromised, especially for endurance activities, necessitating specific training and nutritional strategies for athletes.

High Altitude Physiology

Reduced Oxygen Availability and Physiological Responses

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• High altitude environments decrease barometric pressure and partial pressure of oxygen (PO2), causing hypoxia in the body
• Acute exposure to high altitude triggers increased ventilation rate and heart rate to compensate for reduced oxygen
• Pulmonary vasoconstriction occurs, increasing pulmonary artery pressure and potentially straining the right ventricle
• Reduced oxygen availability decreases arterial oxygen saturation (SaO2) and oxygen delivery to tissues
• Exercise capacity, particularly maximal oxygen uptake (VO2max), significantly reduces due to decreased oxygen availability (can decrease by 1-2% for every 100m above 1500m altitude)
• Acute mountain sickness (AMS) may occur during initial exposure, characterized by headache, nausea, fatigue, and sleep disturbances (typically occurs above 2500m)

Altitude-Induced Physiological Changes

• Hemoglobin's oxygen affinity increases, improving oxygen uptake in the lungs but potentially reducing oxygen release to tissues
• Sympathetic nervous system activity increases, leading to elevated heart rate and blood pressure
• Fluid balance shifts occur, often resulting in initial diuresis and subsequent hemoconcentration
• Altered substrate metabolism favors increased carbohydrate utilization over fat oxidation during exercise
• Oxidative stress increases due to hypoxia-induced free radical production
• Cognitive function may be impaired, affecting decision-making and reaction times during exercise (noticeable above 3000m)

Acclimatization to Altitude

Respiratory and Cardiovascular Adaptations

• Ventilatory acclimatization increases resting ventilation and hypoxic ventilatory response over time (typically begins within hours and continues for weeks)
• Hematological adaptations elevate erythropoietin production, increasing red blood cell count and hemoglobin concentration (takes several weeks to months)
• Cardiovascular acclimatization initially increases cardiac output, gradually returning to near sea-level values as other adaptations occur
• Pulmonary vasculature undergoes remodeling, potentially leading to right ventricular hypertrophy in long-term high-altitude residents
• Oxygen extraction by tissues improves through increased capillarization and myoglobin content in skeletal muscle

Cellular and Metabolic Adaptations

• Cellular adaptations increase mitochondrial density and efficiency, enhancing oxygen utilization (takes several weeks)
• Enhanced capillarization in skeletal muscle improves oxygen delivery to working tissues
• Metabolic adjustments increase reliance on carbohydrates as a fuel source during exercise
• Glucose uptake by muscles improves, enhancing energy availability
• Acclimatization typically takes 1-3 weeks, with some adaptations continuing for several months
• Individual variations in acclimatization are influenced by factors such as genetics, fitness level, and altitude exposure history (some people may acclimatize faster or more completely than others)

Altitude and Performance

Aerobic Performance Impacts

• Aerobic performance significantly impairs at high altitudes due to reduced oxygen availability and decreased VO2max
• Performance impairment is proportional to altitude (VO2max decreases by approximately 7-9% for every 1000m increase in altitude)
• Endurance events (marathons, long-distance cycling) experience greater performance decrements compared to shorter events
• Lactate threshold occurs at a lower absolute workload but a similar relative percentage of VO2max at altitude compared to sea level
• Perceived exertion during submaximal exercise increases at altitude, affecting pacing and overall performance

Anaerobic Performance and Sport-Specific Effects

• Anaerobic performance is less affected by altitude, relying less on oxygen availability
• Short-duration, high-intensity activities (sprints, weightlifting) may show minimal performance decrements or even improvements at moderate altitudes due to reduced air resistance
• Team sports involving intermittent high-intensity efforts (soccer, basketball) are more severely impacted than short-duration anaerobic activities
• Skill-based performances (archery, shooting) may be affected by cognitive impairments and increased tremor at very high altitudes
• Altitude training can lead to improved sea-level performance through various physiological adaptations, although individual responses vary

Optimizing Exercise at Altitude

Acclimatization and Training Strategies

• Proper acclimatization is crucial, with a recommended period of 1-2 weeks at the competition altitude prior to events
• "Live high, train low" approach can improve sea-level performance while minimizing negative impacts of altitude training (athletes live at 2000-2500m and train at lower altitudes)
• Gradual ascent to higher altitudes (300-500m per day) reduces the risk of altitude sickness
• Interval training at altitude can help maintain exercise intensity and mitigate the loss of VO2max
• Resistance training should be incorporated to maintain muscle mass and strength, which can be affected by prolonged altitude exposure

Nutritional and Hydration Considerations

• Adequate hydration is essential due to increased fluid losses through respiration and diuresis (aim for pale yellow urine color)
• Nutritional strategies should focus on increased carbohydrate intake to support greater carbohydrate utilization at altitude (55-65% of total caloric intake)
• Iron supplementation may benefit athletes with marginal iron status to support increased erythropoiesis (ferritin levels should be monitored)
• Antioxidant-rich foods or supplements may help combat increased oxidative stress at altitude (berries, leafy greens, vitamin C)
• Caffeine consumption can enhance exercise performance at altitude by improving oxygen delivery and reducing perception of effort

Performance Optimization Techniques

• Pacing strategies should adjust to account for reduced aerobic capacity, particularly in endurance events (start conservatively and increase intensity gradually)
• Supplemental oxygen use during recovery periods or between exercise bouts may enhance performance in high-altitude competitions (where permitted by competition rules)
• Pre-acclimatization using intermittent hypoxic exposure or altitude tents can prepare athletes for competition at altitude
• Mental strategies, such as mindfulness and cognitive restructuring, can help manage the increased perceived exertion and discomfort associated with exercise at altitude