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?