Transcript Environment and Exercise

Environment and Exercise
Thermoregulation
Body temperature
• Different
temperatures:
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Surface / Skin
Core body
Tympanic
Esophogeal
Rectal
oral
Regulation
• Regulated by hypothalamus to within 1 degree
(37 + or – 1)
• Fig 11.5 a and b pg 258, 259
• Negative feedback loop
• Thermal receptors in the skin
•  Temperature changes in blood
Mechanisms of Heat Loss/gain
• Radiation
– The release of heat via electromagnetic heat
waves
• Conduction
– Direct transfer of heat through contact with a
liquid, solid, or gas
• Convection
– Carrying heat on air currents
• Evaporation
– Provides the major physiologic defense
against overheating
Primary mechanisms??
• At rest?
• During exercise??
Mechanisms of Heat
Conservation
• Vascular adjustments
– Vasoconstriction of
peripheral blood vessels
• Muscular activity
– Voluntary physical
activity
– Involuntary- Shivering
• Hormonal output
– Increased secretion of E,
NE, thyroxine
Mechanisms Facilitating Heat
Loss
• Circulatory
adjustments
• Evaporation
• Hormonal
adjustments
Circulatory Adjustments
• Two competitive cardiovascular demands
exist during exercise in the heat
– Oxygen delivery to muscles must increase to
sustain exercise energy metabolism
– Peripheral blood flow to the skin must
increase to transport metabolic heat from
exercise for dissipation at the body’s surface
Evaporation depends on
• Surface exposed to
environment
• Temperature and
humidity of air
• Convective air
currents
Clothing
• Cloth traps air next to
skin and warms it to
provide insulation
• However if sweat is
not absorbed and
drawn away from skin
to be kept dry,
clothing loses 90%
insulating property
Exercise in the Heat
Heat
• Beijing
• Fig 11.6 shows that compared to
thermoneutral environments, HR higher
SV lower in hot conditions
• 40-41 degrees- brain sends signals to stop
exercise
Consequences of Dehydration
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Reduced plasma volume
Increased submaximal heart rate
Reduced rate of sweating
Impaired ability to thermoregulate
hyperthermia
• Prevention
– Avoid holding competition when temp >28
degrees
– Drink fluids before and after and have breaks
every 15-30 mins
– clothing
• Treatment
– Immerse in ice bath/ cold water
Clothing for the heat
• Cover as little SA as
possible
• Loose fitting to allow
convective air currents
near skin
• Wet allows increased
evaporation
• Colour
– Dark = absorbs radiant
heat
– Light – reflects radiant heat
Factors Affecting Heat
Tolerance
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Acclimatisation
Exercise training
Age
Gender
Body composition
Hydration
Acclimatisation to heat
• Physiologic adaptive changes that
improve heat tolerance
• Training increases heat tolerance
• As does 9-14 days of exercising
in heat
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Lower Heart rate
Lower skin temp
Lower core body temp
Increased plasma volume
Double sweating capacity (volume),
Greater area of the body is used for
sweating, More dilute
– Sweat response earlier in exercise
session
during exercise
Exercise in the Cold
Cold
• Physiological
– Peripheral Vasoconstriction
– Non shivering thermogenesis
– Shivering
• Behavioural adjustments
– Huddle
– Voluntary movement
– Put more clothes on
– Exercise indoors
Exercise in water in the cold
• Body loses heat 4 x as
fast in cool water as in
air the same
temperature
• Shivering
• Swimming in
18degrees as opposed
to 26 degrees = 500
ml/min more o2
Exercise in the cold
• Increased consumption o2 to compensate
for that used in shivering
• Increased mobilisation FFA’s for fuel
– If low blood glucose reduced shivering 
reduced temperature
• Cold muscle = decreased contractile force
– Particularly when fatigued
– Large inner muscles insulated and protected
– Peripheral muscles  decreased dexterity
Dry Mouth
• Air is warmed and humidified by the
bronchial tract  27/30 degrees
• When air is humidified it takes
moisture from the respiratory tract
• Especially during exercise
• Therefore
– Dry mouth
– Burning throat
– Irritation respiratory passages
Evaluating cold stress
S/A node in heart
slow HR
Frostbite warning signs
• Tingling & numbness
fingers and toes
• Burning sensation –
nose & ears
Acclimatisation to cold
• Genetic- Eskimo
• Habituation- Repeated exposure of
extremities to cold  increased peripheral
blood flow to reduce possibility of frostbite
Exercise in Pollution
Pollution
• Carbon monoxide, sulfur
oxides, nitrogen oxides,
ozone, peroxyacetyl
nitrate, aerosols, soot,
dust and smoke
• Large particles and highly
soluble gases are usually
filtered out in nasal
passages
Effects
• Irritation of the upper
respiratory tract
• 30 min submax
exercise = smoking a
pack of cigarettes
• Carbon monoxide reduces the blood’s
capacity to transport
oxygen to the tissues.
• Asthma attacks
Beijing 2008
•Pollution levels
2-3 x higher than
those deemed
safe by WHO
• Trial to take 1
million cars off the
road to see if
pollution levels go
down
Exercise and Altitude
Exercise at Altitude
– Reduced barometric
pressure
– Reduced partial
pressure of oxygen
(Po2)
– Reduced relative
humidity
– Reduced ambient
temperature
Immediate adjustments to altitude
above 2300 m
• Hyperventilation
– Chemoreceptors detect that not getting
enough oxygen
– Increase ventilation to compensate
–  evaporation fluids respiratory tract
• Cardiovascular
– Increased HR and cardiac output
– At rest and during submaximal exercise
Exercise Capacity at Altitude
• Aerobic capacity
– Progressively decreases as altitude increases
– 1-3.5% reduction Vo2 max every 300m
increase from 1500 m
– Greater rate decline for trained athletes
• Circulatory factors
– Decreased MHR and SV
Acclimatisation
• Adaptive responses
to improve one’s
tolerance to altitude
• 2 weeks to adapt to
2300 m
• Additional 610 m = 1
week
Longer-Term Adjustments
• Cellular adaptations
– Increased capillary density
– Increased mitochondrial densities
• Blood volume– Plasma volume decreases
– Erythropoietin released  increase RBC
• Acid-base adjustment
- Ambient air at altitude contains very little Co2
- Affects gradient of o2/Co2 volumes
- Combined with hyperventilation causes low
Co2  increased pH
Altitude Training
• Acclimation to altitude improves one’s
capacity to exercise at altitude
• However inability to train at equivalent
intensity no improvement Vo2 max on
return to sea level
•  Live High, Train Low
Summary
• Environment critical to optimal
performance
• Be aware of environment in case of
negative effects
• Use to your advantage
– Heat
• Humidity
– Cool
– Pollution
– Altitude