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EXERCISE IN HYPOBARIC ENVIRONMENTS

EXERCISE IN HYPOBARIC ENVIRONMENTS. EXERCISE IN HYPOBARIC ENVIRONMENTS. Conditions at Altitude. w Defined as at least 1,500 m (4,921 ft) above sea level. w Reduced barometric pressure (hypobaric). w Reduced partial pressure of oxygen (PO 2 ). w Reduced air temperature. w Low humidity.

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EXERCISE IN HYPOBARIC ENVIRONMENTS

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  1. EXERCISE IN HYPOBARIC ENVIRONMENTS

  2. EXERCISE IN HYPOBARIC ENVIRONMENTS

  3. Conditions at Altitude w Defined as at least 1,500 m (4,921 ft) above sea level w Reduced barometric pressure (hypobaric) w Reduced partial pressure of oxygen (PO2) w Reduced air temperature w Low humidity w Increase in solar radiation intensity

  4. CONDITIONS AT VARIOUS ALTITUDES oC oF

  5. ΔP: Mechanism for Gas Diffusion Differences in the partial pressures of gases in the alveoli and in the blood create a pressure gradient (ΔP) across the respiratory membrane. This difference in pressures leads to diffusion of gases across the respiratory membrane. The greater the pressure gradient, the more rapidly the gas diffuses across it.

  6. PO2 AND PCO2 IN BLOOD PO2=25

  7. Diffusion of Oxygen into the Pulmonary Capillary from the Alveolus Oxygenation of the blood in the lungs depends on the transit time of the blood in the capillaries: Transit time = capillary volume/blood flow As shown in this graph, transit time is slow enough normally for full oxygenation to occur – the only exceptions are in elite endurance athletes who have exceptionally high maximal cardiac outputs

  8. Carbon Dioxide Transport w Dissolved in blood plasma (7% to 10%) • As bicarbonate ions resulting from the dissociation of carbonic acid (60% to 70%) Carbonic anhydrase CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3− w Bound to hemoglobin (carbaminohemoglobin) (20% to 33%)

  9. Effects of Altitude on PO2 Gradient The reduction in PO2 at altitude decreases the partial pressure gradient between the blood and the tissues and thus lowers oxygen transport. This primarily explains the decrease in endurance sports performance at altitude. PO2 at sea level = 760 mmHg  0.2093 = 159 mmHg PO2 at 8,000 ft = 564 mmHg  0.2093 = 118 mmHg Sea Level8,000 ft Arterial PO2 100 mmHg 60 mmHg Muscle PO240 mmHg40 mmHg ΔPO2 60 mmHg 20 mmHg (diffusion gradient)

  10. Acute Exposure: Ventilation • PO2<110 (PaO2<60), ↑ resting minute pulmonary ventilation (↑ Tidal volume) • More extreme causes ↑ frequency • PO2<110 is the hypoxic threshold • Immediate response much greater (subsequent hypocapnia reduces response)

  11. w Pulmonary oxygen diffusion decreases because of ↓ ΔPO2. w Oxygen transport is slightly impaired; reduced Hb saturation from 98% at sea level to 90-92% at 8,000 ft. . w Thus, VO2max is impaired once you are above 1,600 m. w As PO2 decreases above 1600 m, VO2max decreases linearly. Acute Respiratory Responses to Altitude • Pulmonary ventilation increases because of chemoreceptor response of carotid and aortic bodies to hypoxia (low arterial PO2) • body fluids become more alkaline from blowing off CO2. This is followed by increased excretion of bicarbonate by the kidneys.

  12. . CHANGES IN VO2MAX WITH ALTITUDE Denver – 5280 feet

  13. . VO2MAX RELATIVE TO PO2

  14. . Altitude does not affect VO2max until approximately 1,600 m (5,294 ft). Above this level, the decrease in VO2max is approximately 8-11% for every 1,000 m (3,281 ft). . Effect of Altitude on Aerobic Capacity

  15. . w Initial increase in HR and Q during submaximal work to compensate for less O2; SV is decreased with plasma volume decline . w Decrease in HR, SV, and Q during maximal work, which contributes to the decrease in VO2max. Acute Cardiovascular Responses to Altitude w Initial decrease in plasma volume (more red blood cells per unit of blood, thus more oxygen per unit of blood) How would you explain the immediate drop in plasma volume that occurs when one goes to altitude?

  16. Acute and Chronic Cardiovascular Responses to Altitude during Submaximal Exercise Brooks et al., Exercise Physiology, 2000

  17. Metabolic Responses to Altitude w Increase in anaerobic metabolism w Increase in lactic acid production w Less lactic acid production at maximal work rates at altitude than at sea level because it isn’t possible to exercise at as high an intensity

  18. Acute and Chronic Metabolic Responses to Altitude during Submaximal Exercise Brooks et al., Exercise Physiology, 2000

  19. Acute and Chronic Catecholamine Responses to Altitude during Submaximal Exercise Brooks et al., Exercise Physiology, 2000

  20. w At altitude, endurance activity is affected the most due to the reduced oxygen transport because of low PO2. w Endurance athletes can prepare for competitions at altitude by performing high-intensity endurance training at any elevation to increase their VO2max. . w Anaerobic sprint activities that last 2 min or less are the least affected by altitude. w The thinner air at altitude provides less aerodynamic resistance and less gravitational pull, thus potentially improving sprinting, jumping, and throwing events. Performance at Altitude

  21. . w Decrease in VO2max with initial exposure does not improve much Acclimatization to Altitude w Increase in number of red blood cells (RBC) w Short term decrease in plasma volume, later reversed wIncrease in RBC, hemoglobin, and blood viscosity w Decrease in muscle fiber areas and total muscle area, therefore shorter O2 diffusion distances from capillaries to muscle fiber mitochondria w Increase in capillary density w Increase in pulmonary ventilation

  22. Hb CONCENTRATIONS AT ALTITUDE College Station – 362 feet Denver – 5280 feet

  23. Altitude Training for Sea-Level Performance w Increased red blood cell mass w Not proven that altitude training improves sea-level performance w Difficult to study since intensity and volume are reduced at altitude – thus, what you gain in elevated RBC, you lose because of reductions in training intensity w Live at high altitude and train at lower altitudes—living high/training low

  24. LIVING HIGH, TRAINING LOW 3,000 km time was tested at sea level before and after 27 days of training at 4,100 ft. and living at 8,200 ft. The mean increase in 3,000 km time was 1.1%, and the mean increase in VO2max was 3.2%.

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

  26. Acute Altitude Sickness w Nausea, vomiting, dyspnea, insomnia w Appears 6 to 96 h after arrival at altitude w May result from carbon dioxide accumulation w Avoid by ascending no more than 300 m (984 ft) per day above 3,000 m (9,843 ft)

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