Exercise at Altitude

1. chapter 12 Exercise at Altitude

2. Learning Objectives • Find out what conditions in hypobaric environments (at altitude) limit physical activity • Learn the physiological adjustments that accompany acclimatization to altitude • Discern whether an endurance athlete who trains at altitude can perform better at sea level • Learn about the health risks of acute exposure to altitude

3. Conditions at Altitude • At least 1,500 m (4,921 ft) above sea level • Reduced barometric pressure (hypobaric) • Reduced partial pressure of oxygen (PO2) • Sea level PO2 = 0.2093 x 760 mmHg = 159 mmHg • Altitude PO2 = 0.2093 x (barometric pressure; e.g., 110 mmHg at 3,000 m or 9,840 ft) • Reduced air temperature • Decreased water vapor pressure • Increase in solar radiation intensity

4. Differences in Atmospheric Conditions at Sea Level up Through an Altitudeof 9,000 m (29,520 ft)

5. High Altitude Environments Key Points • Altitude represents a hypobaric environment • Percentages of gases remain constant but the partial pressures of the gases decrease • Air at altitude is dry • Because the atmosphere is thinner and drier, solar radiation is more intense, which is magnified by snow cover

6. Respiratory Responses at Altitude • Acute increases in rate and depth of ventilation • Chemoreceptors are stimulated by low PO2 • Respiratory alkalosis • Left shift in the oxyhemoglobin saturation curve • Limits the rise in ventilation, but this is overridden by hypoxic drive • Low arterial blood PO2 (hypoxemia) is a reflection of low alveolar PO2

7. Comparison of the Partial Pressureof Oxygen in the Inspired Airand in Body Tissues

8. The S-Shaped Oxyhemoglobin Dissociation Curve at Sea Level and Altitude

9. Reductions in PO2 and Endurance Performance The reduction in PO2 at altitude affects the partial pressure gradient between the blood and the tissues and thus oxygen transport. This explains the decrease in endurance performance at altitude.

10. Cardiovascular Responsesto Altitude: Blood Volume • Acute altitude exposure decreases plasma volume (~25%) • Respiratory water losses • Increased urine production • Increased hematocrit • Chronic altitude exposure increases blood volume • Triggers the release of erythropoietin (EPO) from the kidney to stimulate red blood cell production • Increased blood volume compensates for the lower PO2

11. Cardiovascular Responsesto Altitude: Cardiac Output • Cardiac output is increased at rest and during submaximal exercise • Acute exposure results in a decrease in stroke volume and an increase in heart rate • Increase in HR and cardiac output peaks after 6-10 days at altitude • Decrease in maximal stroke volume and maximal heart rate • Decreased sympathetic responsiveness

12. Metabolic Responses to Altitude • Basal metabolic rate increases • Increased thyroxin and catecholamines • Acute decline in appetite • Increased reliance on carbohydrates for fuel at rest and during exercise • Lactate paradox

13. Cardiovascular Responses to Altitude Key Points • There is a decreased PO2 throughout the body • With acute altitude exposure, pulmonary ventilation increases, pulmonary diffusion is maintained, but oxygen transport is slightly impaired • Oxygen uptake by the muscle is impaired due to a reduced diffusion gradient • Initially, decreased plasma volume increases red blood cell concentration, allowing more O2 to be transported per unit of blood (continued)

14. Cardiovascular and Metabolic Responses to Altitude (continued) Key Points • Initially, cardiac output during submaximal work increases to compensate for decreased O2 content through an increase in heart rate • During maximal work, stroke volume and heart rate are lower, resulting in decreased cardiac output • Oxygen delivery and uptake are impaired • Metabolic rate increases by increased sympathetic nervous system activity • Increased reliance on carbohydrates for fuel during rest and exercise

15. Changes in Maximal Oxygen Uptake With Decrements in Barometric Pressure and Partial Pressure of Oxygen Data from E.R. Buskirk et al., 1967, "Maximal performance at altitude and on return from altitude in conditioned runners," Journal of Applied Physiology 23: 259-266.

16. . VO2max Relative to the Partial Pressure of Oxygen of the Inspired Air Adapted, by permission, from J.B. West et al., 1983, “Maximal exercise at extreme altitudes on Mount Everest,” Journal of Applied Physiology 55: 688-698.

17. Anaerobic Sprinting, Jumping,and Throwing Activities • Anaerobic sprint activities lasting less than a minute or two are not impaired • Sprinting, jumping, and throwing activities might be improved due to the thinner air and less aerodynamic resistance to movement

18. Exercise and Sport Performance at Altitude Key Points • Prolonged endurance performance suffers the most at high altitude because oxidative energy production is limited • VO2max decreases in proportion to the decrease in atmospheric pressure • Anaerobic sprint activities lasting < 2 minutes are not impaired at moderate altitude • Sprinting, jumping, and throwing activities might be improved due to the thinner air and less aerodynamic resistance to movement .

19. Acclimatization to Altitude: Pulmonary and Blood Adaptations • Pulmonary adaptations • The increased resting ventilation rate levels off at a value ~40% higher than at sea level • Submaximal exercise ventilation rate plateaus at ~50% higher • Ventilation during exercise remains elevated at altitude and is more pronounced at higher intensities • Blood adaptations • ↑ Number of red blood cells, polycythemia • ↑ Plasma volume • ↑ Hemoglobin content • ↑ Oxygen-carrying capacity

20. Hemoglobin (Hb) Concentrationsof Men Living at Various Altitudes

21. Acclimatization to Altitude: Muscle and Cardiovascular Adaptations • Muscle adaptations • Decrease in muscle fiber cross-sectional area and total muscle • Reduced mitochondrial and glycolytic enzyme activities • Increased capillary supply • Cardiovascular adaptations • Decrease in VO2max with initial exposure and does not improve with continued exposure .

22. Acclimatizationto Altitude Adaptations Key Points • Hypoxic conditions stimulate red blood cell production • Overall there is an increase in total blood volume and an increase in oxygen-carrying capacity • Muscle mass and total body weight decrease as a result of dehydration, appetite suppression, and protein breakdown in muscles • Muscle adaptations include decreased fiber area, increased capillary supply, and decreased metabolic enzyme activities • Work capacity improves but the decrease in VO2max does not improve .

23. Altitude Training for Sea-Level Performance • Increases red blood cell mass on return to sea level • Existing research does not support the assertion that altitude training improves sea-level performance • Difficult to study since intensity and volume of training are reduced at altitude • Live at moderate altitudes and train at low altitudes, where training intensity is not compromised

24. Living High, Training Low Improvements in race time in elite male and female runners and college male and female runners following four weeks of living at altitude but training at 1,250 m

25. Training for Optimal Altitude Performance • Compete within 24 hours of arrival at altitude • Train at 1,500 to 3,000 m above sea level for a minimum of 2 weeks before competing • Increase VO2max at sea level to be able to compete at a lower relative intensity .

26. Altitude Training Key Points • Most studies show that training at altitude leads to no significant improvements in performance • Living at high altitudes and training at low altitudes may be the best alternative • Athletes who must perform at altitude should do so within 24 hours of arrival • Athletes could train at altitude (1,500 to 3,000 m) for a minimum of 2 weeks

27. Acute Altitude Sickness (AAS) • Occurs in 7% of male and 22% of female recreational athletes • Symptoms include headache, impaired vision, sleep disturbances, nausea, interrupted breathing patterns (Cheyne-Stokes breathing) • Low ventilatory responses to hypoxia, resulting in CO2 accumulation • Avoid by ascending gradually • no more than 300 m (984 ft) per day above 3,000 m (9,843 ft)

28. High-Altitude Pulmonary Edema (HAPE) • Life-threatening accumulation of fluids in the lungs • May be related to pulmonary vasoconstriction-induced blood clot formation in the lungs • Occurs in unacclimatized people who ascend rapidly • Symptoms are shortness of breath, persistent cough, chest tightness, excessive fatigue, blue lips and fingernails, mental confusion • Treatments include the administration of supplemental oxygen and movement to lower altitude

29. High-Altitude Cerebral Edema(HACE) • Accumulation of fluid in the cranial cavity • Symptoms are mental confusion, lethargy, and ataxia, progressing to coma and death • Most cases occur above 4,300 m (14,108 ft) • Cause is unknown • Treatment includes administration of supplemental oxygen and movement to lower altitude

30. Health Risks of Acute Exposure To Altitude Key Points • AAS causes headaches, nausea, dyspnea, and insomnia, which usually appear 6 to 48 hours after arrival • Exact cause of AAS is not known but may result from the combination of hypoxia and CO2 accumulation in the tissues • AAS can be avoided by slow gradual ascent • HAPE and HACE are life-threatening conditions involving accumulation of fluid in the lungs and cranial cavities, respectively • HAPE and HACE are treated by O2 administration, hyperbaric bags, and descent