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 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 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 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  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 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 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 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 dehydra-tion, 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 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 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