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BPK 142 (161)

Altitude and Performance

6 Pages

Biomedical Physio & Kines
Course Code
BPK 142
Craig Asmundson

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Altitude and Performance 1 Thought Questions 1. How does it seem that exercise is more tiring at altitude than at sea level? 2. How is the physical environment changed at altitude? 3. How does the body respond to reduced oxygen pressures (hypoxia)? 4. Why is maximal exercise reduced ataltitude? 5. Will a person adapt to altitude after a period of time? 6. Will training at altitude be beneficial to performance on returning to sea level? Definitions PO 2 partial pressure of oxygen; measures how well your lungs bring oxygen into your bloodstream Ambient air = untreated air Oxyhemoglobin dissociation curve= amathematical relationship, that is viewed as a graph, showing the amount of oxygen that combines with hemoglobin as a function of the partial pressure of oxygen Acclimatized = adaptation to a new climate (such as temperature, altitude, etc) Hypoxia = deficiency in the amount of oxygen reaching the tissues 2,3 DPG = present in RBC; binds with greater affinity to deoxygenated hemoglobin than it does to oxygenated hemoglobin Physics of Altitude Medium = 5000 - 10,000 feet = we are concerned with this altitude in relation to athletics High = >10,000 feet = over 40 million people live/work between 10,000-18,000 feet (3048m – 5486m) Barometric (air) pressure decreases when altitude increases. (i.e., as the weight of the column of air above the point of measurement decreases).  The chemical composition is the same up to 20,000m PO 2n dry ambient air @ sea level =.209 x 760 mm Hg = 160 mm Hg PO in dry ambient air @ 10,000 feet = .209 x 510 mm Hg =107 mm Hg 2 PO 2n dry ambient air @ summit of MtEverest (29,028 ft) = .209 x 250 mm Hg =52 mm Hg Oxyhemoglobin dissociation curve– minimal change in percent saturation of hemoglobin is observed with decreasing PO 2ntil 10,000 ft. Measurable negative effects on VO2MAX have been seen as low as 4000 ft. Critical alveolar P2 when an unacclimatized person loses consciousness within a fewminutes during acute exposure to hypoxia occurs at 23,000 ft.  Decreased airdensity  decreased external air resistance external work decreased at altitude in sprint-type activities (high velocities) + less air resistance.  Temperature decreases linearly by 6.5 C per 1000m or 2 C per 1000ft.  Increasing altitude = increasinglydry air  water loss via respiratory tract higher at high altitudes Altitude and Performance 2  Solar radiation = UV radiationmore intense at higher altitudes sunburn and snow blindness  Force of gravity decreased with distance from earth’s center Immediate and Longer Adjustments to Altitude Hypoxia Cardiovascular System At rest, the Fick equation states t2at O uptake equals cardiac output times the arterial-mixe2 venous O content difference. This is expressed asVO 2= (HR x SV ) x C a 2– C V 2) VO 2 oxygen uptake, SV = stroke volume, HR = heart rC a,2 = arterial2O contenCVO 2 = venous O2content  Increase altitud decrease CaO 2 o To compensate, cardiac output initially increases for rest + submaximum exercise due to increase inHR o During the 1 week at the higher altitude, cardiac output falls to or below sea level values for the same VO 2ut there is a progressive increase 2n O extraction  More efficient 2 delivery  Most important long-term (~2 weeks) adaptation to altitude = increase in the b2ood’s O carrying capacity  [Hemoglobin] starts increasing during the first 2 days at altitude due to a decrease in plasma volume and an increase in RBC production by bone marrow. o These haematological changes are dependent on adequate iron intake.  Women needmore thanmen due to menstruation.  High altitude natives and well-acclimatized individuals, [hemoglobin] may be up to 50% above normal! Left shift (high affinity fo2 O )Right shift (low affinity for2O ) Temperature Decrease Increase 2,3-DPG Decrease Increase p(CO2) Decrease Increase p(CO) Increase Decrease Increase (alkalosis) Decrease (acidosis) pH (Bohr effect) Concentration of 2,3 DPG within RBC increaesshift 2 dissociation curve to rghunload more O2at tissues for a given capillPOy2.  Even after several months of acclimatizatVOn2MAX still remains remarkably below sea-level values. Pulmonary System Decreased alveolarPO 2 decreased arterialPO 2 stimulation of aortic & carotid chemoreceptors increase in ventilation  increase An 2 O ana 2 O hyperventilation  decreaPACO 2 and PaCO 2  increase in blood pH (respiratory alkalosis)  plasma bicarbonate levels decrease during first 2 days because kidneys excrete excess HCO to compensate pH 3  After the acid-base balance is corrected, hyperventilation persists during acclimatization.  Within a week at high altitude, a new levVlEis attained (40-100% above sea level values). Altitude and Performance 3 Sensory and Mental Function  At 10,000 feet o 30% decrease in visual acuity o 25% decrease in light sensitivity o 25% decrease in attention span  At 14,800 to 18,000 feet o 15-20% decrease in cognition and recall o 25% decrease in pursuit tracking ability  At 20,000 feet o 25% decrease in reaction time Responses to Exercise  VO 2MAX decreases 3-3.5% per 1000 feet above 5000 feet.  At 14,000 feet, VO2MAXhas decreased approximately 30%. This is due to: a. Decreased O c2ntent of arterial blood  decreased a-vO d2fference in maximal exercise b. After acclimatization: Decrease in maximal cardiac output due to decrease inmaximum HR and SV. Decrease in SV MAXis probably due to reduction in venous return which is caused by the decreased blood volume (Starling mechanism) Percentage reduction in VO = equal in both trained and untrainedindividuals. 2MAX  VO 2s the same at altitude as at sealevel for the same submaximal workload. o HOWEVER, HR and minute ventilation will be greater. During heavy exercise, muscle/blood lactate levels are higher at altitude for any given workload for2 reasons: a. Since the VO 2MAXis reduced, any given workload now requires a higher percentage of the V2MAXto perform. b. Reduced blood buffering capacity due to excretion of a certain amount of bicarbonate via kidneys. Therefore, there is a higher level of perceived exertion for any workload. Acclimatization Limits Highest permanent settlement is located at 17,000 feet in the Andes. Acclimatization stops and physical conditions and mental function start to deteriorate above 17,000 feet. Time Required for Acclimatization The longer you stay at altitude, the better you perform aerobically but it will never reach sea level values. Number of days needed to acclimatize depends on the altitude: 9,000 feet  7-10 days 12,000 feet  15-21 days 15,000 feet  21-25 days The time required depends largely on the individual. Some people may never acclimatize and will contin
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