Chapter 1 7 Environmental Physiology. Section I: Exercise When Exposed to Altered Pressure. Exercise at Increased Altitude.
Section I: Exercise When Exposed to Altered Pressure
Exercise at Increased Altitude
As altitude increases, there is a decrease in pressure. This reduced pressure causes air molecules to be more dispersed. Thus, for a given air volume, even though the relative presence (gas fraction) of a gas remains the same, there is less of a given gas.
PO2 in air = 760 mmHg x 0.2093 = 159 mmHg
At Pikes Peak, CO (4,000 m or 14,300 ft)
PO2 in air = 430 mmHg x 0.2093 = 90 mmHg
meters feetPressure (Torr)PIO2 (Torr) PAO2 (Torr)SaO2 (%)
1 Torr = 1 mmHg ; 1 m = 3.28 ft ; PB = 760 [e-(m/7924)] ; PIO2 = (PB - 47) x 0.2093 ;
PAO2 ~ (PB - 47) x 0.146 ; SaO2 approximated from %O2-Hb dissociation curve
During steady state exercise
Percent change (%)
Percent change (%)
Decreases in VO2max During Acute Hypoxic Exposure
-9.2%/1,000 m > 1,500 m
1,500 m ~ 5,000 ft
Is this difference a beneficial or detrimental adaptation?
Does living at altitude improve exercise tolerance at altitude?
Does training at altitude improve exercise tolerance at sea level? ???
This question has not adequately been answered. However, there are recent findings that may indicate a benefit of sleeping at altitude (> 7,000 ft) and training at low-moderate altitude (< 7,000 ft).
Exercise During Hyperbaria
Hyperbaria refers to exposure to increased pressure above 1 atmosphere (atm = 760 mmHg).
When submerged in sea water, pressure increases by 1 atm every 10 m. In fresh water, the pressure change is not as great and approximates 10.4 m.
Section II: Exercise And Thermal Stress
Dehydration - decrease in total body water. Occurs at a faster rate during exercise in hot and/or humid environments
sweat rates can to 2-3 L/Hr
Deleterious effects of dehydration on exercise occur with as little as fluid loss equal to 2% body weight.
For a 70 kg male; 70 x 0.02 = 1.4 kg ~ 1.4 L
This could occur with as little as 30 min of exercise!!!!
Hyperthermia - increased body temperature resulting from body heat storage
Physiological changes during dehydration
Improving Exercise Tolerance During Heat Exposure
Acclimation - chronic adaptations induced by exposure to artificial environmental conditions
(eg. environmental chambers, sauna, exercise)
Acclimatization - chronic adaptations induced by exposure to foreign a foreign climat
(eg. geographical relocation)
Chronic adaptations to exercise and exercise in a hot environment that improve acclimation to exercise in the heat
Heat Illness, Heat Exhaustion and Heat Stroke
These conditions are more severe clinical manifestations of heat exposure.
Heat Exhaustion - the decreased cardiovascular function that accompanies dehydration and mild hyperthermia
Heat Stroke - when heat stress continues, or is worsened beyond that of heat exhaustion (core temp > 39.5 C), physiological symptoms progress to CNS dysfunction - disorientation, confusion, psychoses
Heat exhaustion and heat stroke are both heat illnesses. However, heat stroke can be potentially lethal due potential organ damage and failure.
Evaluating Environmental Conditions For Risk of
An index has been developed that incorporates all contributors to thermal heat stress - Wet Bulb Globe Index (WBGI)
Dry bulb temperature - measure of air temperature
Black bulb temperature - measure of the potential for radiative heat gain
Wet bulb temperature - measure of the potential for evaporative cooling
WBGI = (0.7 x Tw) + (0.2 x Tb) + (0.1 x Td)
The relative risks for heat injury at different ranges of the WBGI
Section III: Human Function and Performance During Gravitational Challenge
The early space programs of the USA and Russia revealed that prolonged exposure to microgravity was detrimental to human physiology.
The earth has a reference gravitational force = 1 g
The moon’s gravitational force = 0.17g
Outside a planetary orbit (eg. Space Shuttle), gravitatonal force = 0g
Research models that have been used to mimic physiological responses to microgravity are,
head-down bed rest lower body negative pressure tilt testing
Physiological Effects of Exposure to Microgravity
Section IV: Exercise And Air Pollution