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Chapter 13

Chapter 13. Exercise at Altitude. Chapter 13 Overview. Environmental conditions at altitude Physiological responses to acute altitude exposure Exercise and sport performance at altitude Acclimation: prolonged exposure to altitude Altitude: optimizing training, performance

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Chapter 13

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  1. Chapter 13 • Exercise at Altitude

  2. Chapter 13 Overview • Environmental conditions at altitude • Physiological responses to acute altitude exposure • Exercise and sport performance at altitude • Acclimation: prolonged exposure to altitude • Altitude: optimizing training, performance • Health risks of acute exposure to altitude

  3. Introduction to Exercise at Altitude • Barometric pressure (Pb) ~760 mmHg at sea level • Partial pressure of oxygen (PO2) • Portion of Pb exerted by oxygen • 0.2093 x Pb ~159 mmHg at sea level • Reduced PO2 at altitude limits exercise performance • Hypobaria • Reduced Pb seen at altitude • Results in hypoxia, hypoxemia

  4. Environmental Conditions at Altitude • 1644: Torricelli develops mercury barometer • 1648: Pascal demonstrates reduced Pb at high altitudes • 1777: Lavoisier describes O2 and other gases that contribute to Pb • 1801: Dalton’s Law of Partial Pressures • Late 1800s: effects of hypoxia on body recognized

  5. Environmental Conditions at Altitude • Sea level (<500 m): no effects • Low altitude (500-2,000 m) • No effects on well-being • Performance may be , restored by acclimation • Moderate altitude (2,000-3,000 m) • Effects on well-being in unacclimated people • Performance and aerobic capacity  • Performance may or may not be restored by acclimation

  6. Environmental Conditions at Altitude • High altitude (3,000-5,500 m) • Acute mountain sickness • Performance , not restored by acclimation • Extreme high altitude (>5,500 m) • Severe hypoxic effects • Highest settlements: 5,200 to 5,800 m • For our purposes, altitude = >1,500 m • Few (if any) physiological effects <1,500 m

  7. Environmental Conditions at Altitude • Pb at sea level exerted by a 24 mi tall air column • Sea level Pb: 760 mmHg • Mt. Everest Pb: 250 mmHg • Pb varies, air composition does not • 20.93% O2, 0.03% CO2, 79.04% N2 • PO2always = 20.93% of Pb • 159 mmHg at sea level, 52 mmHg on Mt. Everest • Air PO2 affects PO2 in lungs, blood, tissues

  8. Figure 13.1

  9. Environmental Conditions at Altitude • Air temperature at altitude • Temperature decreases 1 °C per 150 m ascent • Contributes to risk of cold-related disorders • Humidity at altitude • Partial pressure of water: PH2O • Cold air holds very little water • Air at altitude very cold and very dry • Dry air  quick dehydration via skin and lungs

  10. Environmental Conditions at Altitude • Solar radiation  at high altitude • UV rays travel through less atmosphere • Water normally absorbs sun radiation, but low PH2O at altitude can’t • Snow reflects/amplifies solar radiation

  11. Physiological Responses to Acute Altitude Exposure • Pulmonary ventilation  immediately • At rest and submaximal exercise (but not maximal exercise) –  PO2 stimulates chemoreceptors in aortic arch, carotids –  Tidal volume for several hours, days •  Ventilation at altitude = hyperventilation • Alveolar PCO2 CO2 gradient, loss • Blowing off CO2 = respiratory alkalosis

  12. Physiological Responses to Acute Altitude Exposure • Respiratory alkalosis = high blood pH • Oxyhemoglobin curve shifts left • Prevents further hypoxia-driven hyperventilation • Kidneys excrete more bicarbonate • Minimizes blood buffering capacity • Reverses alkalosis, blood pH decreases to normal

  13. Physiological Responses to Acute Altitude Exposure • Pulmonary diffusion • At rest, does not limit gas exchange with blood • At altitude, alveolar PO2 still = capillary PO2 • Hypoxemia a direct reflection of low alveolar PO2 • Oxygen transport –  Alveolar PO2  O2 hemoglobin saturation • Oxyhemoglobin dissociation curve shifts left • Shape and shift of curve minimize desaturation

  14. Figure 13.2

  15. Figure 13.3

  16. Physiological Responses to Acute Altitude Exposure • Gas exchange at muscles  • PO2 gradient at muscle  • Sea level: 100 – 40 = 60 mmHg gradient • 4,300 m altitude: 42 – 27 = 15 mmHg gradient • O2 diffusion into muscle significantly reduced • Location of gradient change critical • Hemoglobin desaturation at lungs  little/no effect –  PO2 gradient at muscle  exercise capacity

  17. Physiological Responses to Acute Altitude Exposure • Short term: plasma volume  within few hours • Respiratory water loss,  urine production • Lose up to 25% plasma volume • Short-term  in hematocrit, O2 density • Red blood cell count  after weeks/months • Hypoxemia triggers EPO release from kidneys –  Red blood cell production in bone marrow • Long-term  in hematocrit

  18. Physiological Responses to Acute Altitude Exposure • Cardiac output  (despite  plasma volume, stroke volume) • At rest and submaximal exercise (not maximal) • Delivers more O2 to tissues per minute –  Sympathetic nervous system activity   HR • Inefficient, short-term adaptation (6-10 days) • After few days, muscles extract more O2 –  (a-v)O2 difference • Reduces demand for cardiac output

  19. Physiological Responses to Acute Altitude Exposure • Qmax = SVmax x HRmax • SVmax due to  PV • HRmax due to  SNS responsiveness •  PO2 gradient + Qmax = VO2max

  20. Physiological Responses to Acute Altitude Exposure • Basal metabolic rate  –  Thyroxine secretion –  Catecholamine secretion • Must  food intake to maintain body mass • More reliance on glucose versus fat •  Anaerobic metabolism   lactic acid • Lactic acid production  over time • No explanation for lactate paradox

  21. Table 13.1

  22. Physiological Responses to Acute Altitude Exposure • Dehydration occurs faster • Water loss through skin, kidneys/urine • Exacerbated by sweating with exercise • Must consume ~3 to 5 L fluid/day • Appetite declines at altitude • Paired with  metabolism  500 kcal/day deficit • Athletes/climbers must be educated about eating at altitude • Maintain iron intake to support  in hematocrit

  23. Exercise and Sport Performance at Altitude • VO2max as altitude  past 1,500 m • Atmospheric PO2 <131 mmHg • Due to  arterial PO2 and Qmax • Drops 8 to 11% per 1,000 m ascent • Mt. Everest ascent study, 1981 • VO2max from 62 to 15 ml/kg/min • If sea level VO2max <50 ml/kg/min, could not climb without supplemental oxygen

  24. Figure 13.4

  25. Figure 13.5

  26. Exercise and Sport Performance at Altitude • Aerobic exercise performance affected most by hypoxic conditions at altitude • VO2max as a percent of sea level VO2max • Given task still has same absolute O2 requirement • Higher sea-level VO2max easier perceived effort • Lower sea-level VO2max harder perceived effort

  27. Exercise and Sport Performance at Altitude • Anaerobic performance unaffected • For example, 100 to 400 m track sprints • ATP-PCr and anaerobic glycolytic metabolism • Minimal O2 requirements • Thinner air  less air resistance • Improved swim and run times (up to 800 m) • Improved jump distances • Throwing events, varied effects

  28. Acclimation: Prolonged Exposure to Altitude • Acclimation affords improved performance, but performance may never match that at sea level • Pulmonary, cardiovascular, skeletal muscle changes • Takes 3 weeks at moderate altitude • Add 1 week for every additional 600 m • Lost within 1 month at sea level

  29. Figure 13.6a

  30. Figure 13.6b

  31. Acclimation: Prolonged Exposure to Altitude • Pulmonary adaptations –  Ventilation at rest and during submaximal exercise • Resting ventilation rate 40% higher than at sea level (over 3-4 days) • Submaximal rate 50% higher (longer time frame) • Blood adaptations • EPO release  for 2 to 3 days • Stimulates polycythemia ( red blood cell count, hematocrit) • Elevated red blood cell count for 3+ months

  32. Acclimation: Prolonged Exposure to Altitude • Consequences of polycythemia • Hematocrit at sea level: ~45% • Hematocrit at 4,500 m: ~60% • Hemoglobin  proportional to elevation • Oxyhemoglobin curve may or may not shift • Plasma volume , then  • Early loss  hematocrit prior to polycythemia • Later increase  stroke volume, cardiac output

  33. Figure 13.7

  34. Acclimation: Prolonged Exposure to Altitude • Muscle function and structure changes • Cross-sectional area  • Capillary density  –  Muscle mass due to weight loss, possibly protein wasting • Muscle metabolic potential  • Mitochondrial function and glycolytic enzymes  • Oxidative capacity 

  35. Acclimation: Prolonged Exposure to Altitude • Study of runners showed no major cardiovascular adaptations • 2 months at altitude = more tolerant of hypoxia • But no changes in aerobic capacity • Possible cause: reduced atmospheric PO2 inhibited training intensity at high altitude

  36. Altitude: Optimizing Training and Performance • Altitude acclimation confers certain advantageous adaptations for competing • Training possibilities for competition • Train high, compete low? • Train high, compete high? • Train low, compete high? • Live high, train low, compete high?

  37. Altitude: Optimizing Training and Performance • Hypoxia at altitude prevents high-intensity aerobic training • Living and training high leads to dehydra-tion, low blood volume, low muscle mass • Value of altitude training for sea-level performance not validated • Value of live high, train low?

  38. Altitude: Optimizing Training and Performance • Two strategies for sea-level athletes who must sometimes compete at altitude 1. Compete ASAP after arriving at altitude • Does not confer benefits of acclimation • Too soon for adverse effects of altitude 2. Train high for 2 weeks before competing • Worst adverse effects of altitude over • Aerobic training at altitude not as effective

  39. Altitude: Optimizing Training and Performance • Live high, train low: best of both worlds • Permits passive acclimation to altitude • Training intensity not compromised by low PO2 • Outcome tested on 5 k run time trial • Live high, train high: no improvement • Live low, train low: no improvement • Live high, train low: significant improvement

  40. Altitude: Optimizing Training and Performance • Live high, train low more recently validated • Lived at 2,500 m, trained at 1,250 m • Pre- and posttesting at sea level • Aerobic performance improved 1.1% • VO2max improved 3.2%

  41. Effects of Live High, Train Low on Aerobic Performance

  42. Altitude: Optimizing Training and Performance • Artificial altitude training • Attempt to gain benefits of hypoxia at sea level • Breathe hypoxic air 1 to 2 h/day, train normally • No improvements • Alternating train high, train low • Training high stimulates altitude acclimation • Training low doesn’t lose altitude acclimation • Training low permits maximal aerobic training

  43. Altitude: Optimizing Training and Performance • Live high, train low at sea level • Sleep and live in hypoxic apartment ( PN2, PO2) • Train normally • Not scientifically validated yet • Natural live high, train low best approach • Best for elite athletes • Nonelite exercisers may benefit from artificial approaches

  44. Health Risks of Acute Exposure to Altitude • Acute altitude (mountain) sickness • Onset 6 to 48 h after arrival, most severe days 2 to 3 • Headache, nausea/vomiting, dyspnea, insomnia • Can develop into more lethal conditions • Incidence of altitude sickness varies widely •  With altitude, rate of ascent, susceptibility • Frequency: 7 to 22% at 2,500 to 3,500 m • Women have higher incidence than men

  45. Figure 13.8

  46. Health Risks of Acute Exposure to Altitude • Possible causes of altitude sickness • Low ventilatory response to altitude • CO2 accumulates, acidosis • Headache most common symptom • Mostly experienced >3,600 m • Continuous and throbbing • Worse in morning and after exercise • Hypoxia  cerebral vasodilation  stretch pain receptors

  47. Health Risks of Acute Exposure to Altitude • Altitude sickness insomnia • Interruption of sleep stages • Cheyne-Stokes breathing prevents sleep • Incidence of irregular breathing  with altitude • Altitude sickness prevention and treatment • Gradual ascent to altitude • Acetazolamine (+ steroids) • Artificial oxygen, hyperbaric rescue bags

  48. Health Risks of Acute Exposure to Altitude • Altitude  two life-threatening conditions • Both involve edema formation • High-altitude pulmonary edema (HAPE) • High-altitude cerebral edema (HACE) • Can develop from severe altitude sickness • Must be treated immediately

  49. Health Risks of Acute Exposure to Altitude • HAPE causes • Likely related to hypoxic pulmonary vasoconstriction • Clot formation in pulmonary circulation • HAPE symptoms • Shortness of breath, cough, tightness, fatigue –  Blood O2, cyanosis, confusion, unconsciousness • HAPE treatment • Supplemental oxygen • Immediate descent to lower altitude

  50. Health Risks of Acute Exposure to Altitude • HACE causes • Complication of HAPE, >4,300 m • Edemic pressure buildup in intracranial space • HACE symptoms • Confusion, lethargy, ataxia • Unconsciousness, death • HACE treatment • Supplemental oxygen, hyperbaric bag • Immediate descent to lower altitude

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