Hypoxia and exercise
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An archaeic presentation I gave to Athletic Trainers. 12 years later, I think this topic deserves to be re-visited. Much of the information provides a helpful summary of the effects of hypoxia, but the conclusion that altitude training does not affect sea-level performance should be re-assessed taking into consideration more current research.
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Hypoxia and exercise
- 1. Hypoxia and Exercise Stacy Schroeder, ATC, WEMT O’dark:45 morning meeting December 2000
- 2. The significance of Altitude “Thin air” The density ↓ with ascent Everest - 30% of the O2 available in air at sea level High Altitude: 5,000’-12,000’ Very High Altitude: 12K - 18K Extreme altitude: above 18,000’
- 3. Acclimatization Every breath - fewer O2 molecules available (HYPOXIA) Work harder to get O2 (breathe faster) Add physical exertion - body wants even more O2, and it’s getting less. Therefore decreased performance, sickness, death After a week at altitude, cells start to change to help maintain adequate O2
- 4. Understanding O2 Uptake, Transport, and Delivery In the Body We need O2 to do work Working muscles produce CO2 Gas XC btw. Lungs and blood Blood carries O2, nutrients to working muscles Some CO2 in blood is good to stimulate breathing
- 5. Chemoreceptors (McArtle et al., 1996)
- 6. Oxygen Combined with Hemoglobin Hemoglobin (iron) in the blood Anemic athletes: not enough iron, therefore can’t carry as much O2 and can’t sustain even mild aerobic exercise
- 9. Acute Response to Hypoxia HYPERVENTILATION • Increases during first few weeks • Any significant reduction in PO2 in blood stimulates receptors • Aorta, Carotid arteries
- 10. Acute Response to Hypoxia INCREASED CV RESPONSE • With submaximal exercise, HR and CO increase ( ↑ blood flow) • O2 cost of exercise @ altitude is no different than at sea level • Compensate for decreased O2 • Exercise at altitude = harder on the body
- 11. INCREASED CV RESPONSE • With Maximal exercise- increased breathing and increased blood flow still can’t bring enough O2 to tissues
- 13. Longer-Term Adjustments to Altitude ACID-BASE READJUSTMENT • Our body’s chemistry is all out of whack, so kidneys secrete a chemical which helps to restore normal function and allow us to increase our breathing even more
- 14. Longer-Term Adjustments to Altitude DECREASED PLASMA VOLUME INCREASED RBC MASS • hormone released within 15 hours of ascent • More blood cells, more Hb = can carry more O2.
- 15. Longer-Term Adjustments to Altitude CELLULAR CHANGES • Able to “store” more O2 in specific muscles • Encourage O2 release within the cells when the tissues are experiencing low PO2
- 16. Why Should I Care? So If I train at altitude for awhile, my body will make more blood cells, and will carry more O2… and if I come back down to Foothill College I’ll be able to exercise harder and for longer, because I can get more O2 than before, right?
- 17. Your Athletes Want to Know! NOT EXACTLY! • The loss inVO2 max outweighs the benefits of acclimatization • The potential circulatory benefits are lost 2-3 weeks after return to sea level anyway • Too much Hb = thick blood! • Loss of muscle mass
- 18. Exercise Capacities at Altitude SUBMAXIMAL: • Within days/weeks of acclimatization, SV is reduced • Therefore, CO is reduced • Prolonged stay: decreased SV is offset by increased submax HR • But the whole circulatory system is not as efficient during exercise
- 19. Exercise Capacities at Altitude MAXIMAL EXERCISE: • Reduction in max CO after 1 week above 10,000’ • Decreased max HR and SV, therefore decreased blood flow
- 20. Studies on Runners (Buskirk et al., 1967) Highly trained track athletes Flown to Peru (13,124’) Train/acclimate for 40-57 days After 3 days: VO2 max reduced by 29% After 46 days: still 26% lower
- 21. “track meet” with high-altitude natives Not one runner improved his pre-altitude run time Upon return to sea level, still no difference (VO2 max/run time) Longer events: times actually 5% below pre-altitude trials!
- 22. Can Training be Maintained at High Altitude? Exposure to 8,000’ and higher Iron Supplementation?
- 24. In a Nutshell... As altitude increases, there is not as much O2 available in the air This leads to inadequate oxygenation of hemoglobin Not enough O2 = poor aerobic performance Sprints/power not affected
- 26. Reduced PO2 → hypoxia → physiologic responses → improved altitude tolerance at rest and during exercise Immediate: hyperventilation, increased submax CO (via increased HR)
- 27. Longer-term acclimatization greatly improve tolerance to altitude hypoxia • re-establishing chemistry balance • more Hb and red blood cells • more blood flowing to the areas of need (greater capillarization)
- 28. Rate of acclimatization depends on the altitude • noticeable improvements within several days • major adjustments: 2 weeks, but 4- 6 weeks necessary for high altitudes
- 29. Even with acclimatization, altitude still takes its toll on the body • VO2 max is lowered (due to reduced HR and SV) • endurance performance declines
- 30. Adaptations have not been shown to enhance aerobic capacity and performance at sea level • due to decrease in max HR and SV • Training at altitude provides no additional benefit to sea-level performance compared to equivalent training at SL
- 31. Any Questions?
Notas do Editor
- Thin Air: as we go higher in altitude, there is less oxygen available in the air we breath. Therefore, there is less O2 in our lungs (alveoli) and less O2 going to our working muscles Even though there is the same amount of oxygen at both sea level and altitude (~20%), the PO2 (density of the O2 molecules in air) is increasingly reduced as we go higher Everest - unacclimatized = unconscious in 30 seconds! High altitude = Heavenly, Tahoe Very high altitude = Mount Shasta Extreme altitude = Denal (6,000m)i, Everest (8,710m)
- Immediately - increase breathing Increased respirations isn’t enough Body’s structure needs to adapt to demands of altitude
- O2 = fuel for aerobic energy system CO2 = waste product Breathe out CO2, take in O2 Our brain knows when we need O2 by the amount of CO2 floating around in the blood CO2 tells the brain that we need to increase breathing somehow
- In the blood we have a protein called hemoglobin Hemoglobin grabs O2 molecules and carries them through the body
- Decreased arterial PO2 (~6,500’) Stimulates chemoreceptors Modifies inspiratory activity Increases alveolar ventilation (Hyperventilation) Increased PO2 in alveoli Helps to load up more O2 in lungs, which is a rapid response to the decrease in the PO2 of the outside air at altitude
- So increased blood flow will help make up for decreased O2 in arterial blood Even though O2 costs are the same, exercise at altitude = more strenuous. Ex. Exercise at 50% VO2 max (sea level) = 709% VO2 max @ altitude Remember VO2 max lab: VO2 is used as a measurement of exercise intensity (amount of oxygen consuming) So because there is an adjustment in circulation (increase), the oxygen uptake is about the same as at sea level during exercise that is modertely hard (not an all-out maximal effort)
- The body can’t make up for The low amount of O2 in the blood, even with more breaths and blood pumping through faster. The body must make structural adjustments!
- How diffusion works: Particles go from greater concentration to lesser concentration. So if I have a lot of O2 on one side of a membrane, and very little on the other, the O2 will sneak through that membrane to try to make the sides equal If we breathe in a lot of O2, the lungs have very little CO2 in them (b/c not a lot of CO2 in ambient air). The blood on the other side of the lung tries to re-establish the balance, and gives up its CO2 - lets it pass through the barrier. Now we have less-than-normal levels of CO2 in blood. Remember how the level of CO2 stimulates the brain to breathe. The loss of CO2 in the blood causes an upset in the balance of the body. The chemistry of the blood changes, and then the kidneys excrete a substance to bring everything back to normal. When this happens, it makes our respiratory centers of the brain even better, and allows us to increase ventilation even higher to adjust to altitude hypoxia. B/C of increased ventilation (breathing), and there is very little CO2 in the air we breathe, the amount of CO2 in the arterial blood will decrease
- So even if the Hb aren’t carrying as much O2 as they possibly can (at high altitudes the O2 doesn’t stick as well), the body doesn’t mind because now there might be twice as many RBCs and the body s still able to get as much O2 as it needs to work.
- After passing 5,000’, VO2 max decreases linearly at 10% per 3000’ of increase in altitude At 20,500’, VO2 max is about HALF that at sea level! Reduced Max HR, SV * Even after several months of acclimatization, the VO2 max remains significantly below sea-level values because the benefits of acclimatization are offset by the decreased circulatorefficiency in both submaximal and maximal exercise Concentration of hemoglobin is too high (b/c of decreased plasma volume and increased RBCs) So Blood is too thick and flow is restricted Therefore it slows the O2 diffusion to the tissues. Defeats the purpose of having such good O2-carrying capacity! Loss of muscle = long term exposure - b/c: less food, not absorbing as much in intestines, and increased basal metabolic rate
- “track meet” with high-altitude natives - run times considerably slower than pre-altitude times Upon return to sea level, still no difference in VO2 max and running performance
- Exposure to 8,000’ and higher = nearly impossible to train at same intensity as at sea level. Reduction in training intensity may be so great that the athlete cannot maintain peak condition for sea-level competition ( we all know that intensity is one of the biggest determinants of improving VO2 max) -- (Frequency, INTENSITY, Time, Duration) Maybe elite athletes would benefit from periodically returning from high-altitude to sea level for intensive training to help offset any “detraining” that takes place during prolonged high-altitude stay. This wouldn’t interfere with acclimatization and may be beneficial to altitude performance
- Short-term sprints and power performances that depend on energy from the stored phsophates within the muscles are not adversely affected at altitude
- Reduced PO2 and accompanying hypoxia stimulate physiologic responses that improve altitude tolerance at rest and during exercis e