environment and exercise. thermoregulation body temperature different temperatures: –surface /...
TRANSCRIPT
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Environment and Exercise
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Thermoregulation
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Body temperature
• Different temperatures:– Surface / Skin– Core body– Tympanic– Esophogeal– Rectal– oral
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Regulation
• Regulated by hypothalamus to within 1 degree (37 + or – 1)
• Fig 11.5 a and b pg 258, 259• Negative feedback loopThermal receptors in the skin Temperature changes in blood
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Mechanisms of Heat Loss/gainMechanisms 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
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Primary mechanisms??
• At rest?
• During exercise??
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Mechanisms of Heat Conservation
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
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Mechanisms Facilitating Heat Loss
Mechanisms Facilitating Heat Loss
• Circulatory adjustments
• Evaporation
• Hormonal adjustments
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Circulatory AdjustmentsCirculatory 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
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Evaporation depends on
• Surface exposed to environment
• Temperature and humidity of air
• Convective air currents
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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
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Exercise in the Heat
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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
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Consequences of DehydrationConsequences of Dehydration
• Reduced plasma volume
• Increased submaximal heart rate
• Reduced rate of sweating
• Impaired ability to thermoregulate
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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
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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
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Factors Affecting Heat Tolerance
Factors Affecting Heat Tolerance
• Acclimatisation
• Exercise training
• Age
• Gender
• Body composition
• Hydration
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Acclimatisation to heat
• Physiologic adaptive changes that improve heat tolerance
• Training increases heat tolerance• As does 9-14 days of exercising
in heat– 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
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Exercise in the Cold
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Cold
• Physiological– Peripheral Vasoconstriction – Non shivering thermogenesis– Shivering
• Behavioural adjustments– Huddle– Voluntary movement– Put more clothes on– Exercise indoors
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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
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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
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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
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Evaluating cold stress
S/A node in heart slow HR
Frostbite warning signs• Tingling & numbness
fingers and toes• Burning sensation –
nose & ears
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Acclimatisation to cold
• Genetic- Eskimo
• Habituation- Repeated exposure of extremities to cold increased peripheral blood flow to reduce possibility of frostbite
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Exercise in Pollution
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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
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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
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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
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Exercise and AltitudeExercise and Altitude
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Exercise at AltitudeExercise at Altitude
– Reduced barometric pressure
– Reduced partial pressure of oxygen (Po2)
– Reduced relative humidity
– Reduced ambient temperature
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Immediate adjustments to altitude above 2300 m
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
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Exercise Capacity at AltitudeExercise 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
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Acclimatisation
• Adaptive responses to improve one’s tolerance to altitude
• 2 weeks to adapt to 2300 m
• Additional 610 m = 1 week
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• 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
Longer-Term AdjustmentsLonger-Term Adjustments
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Altitude TrainingAltitude 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
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SummarySummary
• Environment critical to optimal performance
• Be aware of environment in case of negative effects
• Use to your advantage– Heat
• Humidity
– Cool– Pollution– Altitude