Transcript Slide 1

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
• Health risks of acute exposure to altitude
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
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
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
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
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
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20.93% O2, 0.03% CO2, 79.04% N2
PO2 always = 20.93% of Pb
159 mmHg at sea level, 52 mmHg on Mt. Everest
Air PO2 affects PO2 in lungs, blood, tissues
Figure 13.1
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
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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
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
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
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
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
Figure 13.2
Figure 13.3
Physiological Responses
to Acute Altitude Exposure
• Gas exchange at muscles 
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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
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
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
Physiological Responses
to Acute Altitude Exposure
•  Qmax =  SVmax x  HRmax
•  SVmax due to  PV
•  HRmax due to  SNS responsiveness
•  PO2 gradient +  Qmax =  VO2max
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
Table 13.1
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
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
Figure 13.4
Figure 13.5
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
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
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
Figure 13.6a
Figure 13.6b
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
Acclimation:
Prolonged Exposure to Altitude
• Consequences of polycythemia
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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
Figure 13.7
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 
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
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• Possible cause: reduced atmospheric PO2
inhibited training intensity at high altitude
Altitude:
Optimizing Training and Performance
• Altitude acclimation confers certain
advantageous adaptations for competing
• Training possibilities for competition
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Train high, compete low?
Train high, compete high?
Train low, compete high?
Live high, train low, compete high?
Altitude:
Optimizing Training and Performance
• Hypoxia at altitude prevents high-intensity
aerobic training
• Living and training high leads to dehydration, low blood volume, low muscle mass
• Value of altitude training for sea-level
performance not validated
• Value of live high, train low?
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
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
Altitude:
Optimizing Training and Performance
• Live high, train low more recently validated
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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%
Effects of Live High, Train Low on
Aerobic Performance
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
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
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
Figure 13.8
Health Risks of Acute Exposure
to Altitude
• Possible causes of altitude sickness
– Low ventilatory response to altitude
– CO2 accumulates, acidosis
• Headache most common symptom
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Mostly experienced >3,600 m
Continuous and throbbing
Worse in morning and after exercise
Hypoxia  cerebral vasodilation  stretch pain
receptors
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
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
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
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