Hypoxia and Exercise Stacy Schroeder, ATC, WEMT O’dark:45 morning meeting December 2000
Jan 14, 2015
Hypoxia and Exercise
Stacy Schroeder, ATC, WEMT
O’dark:45 morning meeting
December 2000
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’
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
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
Chemoreceptors(McArtle et al., 1996)
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
Short Term Exposure
Acute Response to Hypoxia
HYPERVENTILATION• Increases during first few weeks
• Any significant reduction in PO2 in blood stimulates receptors
• Aorta, Carotid arteries
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
INCREASED CV RESPONSE
• With Maximal exercise- increased breathing and increased blood flow still can’t bring enough O2 to tissues
Long-Term Exposure
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
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.
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
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?
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
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
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
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
“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!
Can Training be Maintained at High Altitude?
Exposure to 8,000’ and higher
Iron Supplementation?
We’re Almost There!
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
Anaerobic Exercise
Reduced PO2 hypoxia physiologic responses improved altitude tolerance at rest and during exercise
Immediate: hyperventilation, increased submax CO (via increased HR)
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)
Rate of acclimatization depends on the altitude• noticeable improvements within
several days• major adjustments: 2 weeks, but 4-6
weeks necessary for high altitudes
Even with acclimatization, altitude still takes its toll on the body
• VO2 max is lowered (due to reduced HR and SV)
• endurance performance declines
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
Any Questions?