Learning Objectives

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Learning Objectives
w Find out what conditions in hypobaric
environments (at altitude) limit or contribute to
different types of physical activity.
w Learn the physiological adjustments that
accompany acclimatization to altitude.
w Discern whether an endurance athlete who trains
at altitude can perform better at sea-level.
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Learning Objectives
w Learn what physiological and pathological
problems face scuba divers who descend 30 m or
more.
w Examine what happens to muscles, bones, and
blood in a microgravity environment (in space).
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Conditions at Altitude
w 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
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Did You Know?
The reduction in PO2 at altitude affects the
partial pressure gradient between the blood and
the tissues and thus oxygen transport. This
explains the decrease in endurance sports
performance at altitude.
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Respiratory Responses to Altitude
w Pulmonary ventilation increases.
w Pulmonary diffusion does not change.
w Oxygen transport is slightly impaired.
w Oxygen uptake is impaired.
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Did You Know?
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Cardiovascular Responses to Altitude
w Initial decrease in plasma volume (more red
blood cells per unit)
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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
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Key Points
Performance at Altitude
w At altitude, endurance activity is affected the
most due to reliance on oxygen transport and the
aerobic energy system.
w Anaerobic sprint activities are the least
affected by altitude.
w The thinner air at altitude provides less
aerodynamic resistance and less gravitational
pull, thus potentially improving jumping and
throwing events.
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Acclimatization to Altitude
w Increase in number of red blood cells
w Decrease in plasma volume
w Increase in hemoglobin content and blood
viscosity
w Decrease in muscle fiber areas and total muscle
area
w Increase in capillary density
w Increase in pulmonary ventilation
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Hb CONCENTRATIONS AND ALTITUDE
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Altitude Training for Sea-Level Performance
w Increases red blood cell mass on return to sea
level
w Not proven that altitude training improves
sea-level performance
w Difficult to study since intensity and volume
are reduced at altitude
w Live at high altitude and train at lower
altitudes
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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
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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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High-Altitude Pulmonary Edema (HAPE)
w Shortness of breath, excessive fatigue, blue
lips and fingernails, mental confusion
w Occurs after rapid ascent above 2,700 m (8,858
ft)
w Accumulation of fluid in the lungs which
interferes with air movement
w Cause unknown
w Administer supplemental oxygen and move to
lower altitude
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High-Altitude Cerebral Edema (HACE)
w Mental confusion, progressing to coma and death
w Most cases occur above 4,300 m (14,108 ft)
w Accumulation of fluid in cranial cavity
w Cause unknown
w Administer supplemental oxygen and move to
lower altitude
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Water Immersion and Gas Pressures
Pressure underwater is greater than at sea level.
As pressure increases, volume decreases.
w Descentexternal pressure increases.
w Submersionair already in the body compresses.
w Ascentair taken in at depth expands.
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WATER DEPTH AND AIR VOLUME
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Cardiovascular Responses to Immersion
w Cardiovascular workload decreases
w Plasma volume increases
w Heart rate decreases (even more in cold water)
w At a given exercise effort, heart rate is lower
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OXYGEN UPTAKE AND HEART RATE
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Key Points
Breath-Hold Diving
w Urge to breathe is due to build up of arterial
CO2.
w Gases in body can reduce to no smaller than
residual volume.
w Depth limit is determined by the TLVRV ratio.
w Individuals with larger TLVRV ratios can dive
deeper than those with smaller ratios.
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Key Points
Scuba Diving
w A self-contained underwater breathing apparatus
(scuba) pressurizes the air breathed underwater.
w The length of a dive depends on the diver's
depth.
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HEALTH RISKS OF HYPERBARIC CONDITIONS
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Oxygen Poisoning
w PO2 values exceed 318 mmHg
w Visual distortion, rapid and shallow breathing,
and convulsions
w Tissues are not able to remove O2 from
hemoglobin
w Hemoglobin is then not able to remove CO2
w High PO2 causes vasoconstriction to cerebral
vessels
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Decompression Sickness
w Results from ascending too rapidly
w Aching in elbows, shoulders, and knees, can
cause emboli in blood
w Nitrogen bubbles become trapped in body
w Treat by placing diver in recompression chamber
w Prevent by using chart showing time to ascend
from various depths
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DECOMPRESSION DURING DIVING
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Nitrogen Narcosis
w Nitrogen acts like anaesthetic gas
w Similar to alcohol intoxication
w Depth and pressure increases worsen it
w Also called rapture of the deep
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PNEUMOTHORAX AND EMBOLI FORMATION
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Did You Know?
The Navy uses a technique called saturation
diving to enable divers to stay at great depths
for long periods of time. At a given depth, the
amount of nitrogen that can dissolve in the body
tissues is limited. By staying in a pressurized
environment for 24 hours, the body tissues become
saturated, after which the tissues do not absorb
any more inactive gas for as long as the diver
stays at that depth.
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Key Points
Microgravity Environments
w 1 g is the standard acceleration produced by
gravity.
w Microgravity describes conditions where
gravitational force is less than 1 g.
w Microgravity is used to describe conditions in
space that aren't always 0 g.
w The effects of microgravity on the body are
similar to the effects of detraining.
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Exercise in Microgravity Environments
w Muscle strength decreases
w Cross-sectional areas of ST and FT fibers
decrease
w Bone mineral content in weight-bearing bones
decreases
w Plasma volume decreases
w Transient cardiac output and arterial blood
pressure increases
w Weight decreases (mostly from fluid loss)
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EFFECTS OF BED REST vs SPACE FLIGHT
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Did You Know?
Research shows that exercise during spaceflight
may be an effective countermeasure to prepare
astronauts for successful adaptation on return to
earth. The type and amount of exercise that
produces the best results is still under debate.