thermal regulation & exercise
TRANSCRIPT
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Thermal Regulation & Exercise
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Mechanisms of Body Temperature Regulation Human are homeothermic
During prolonged exercise, illness or extreme
conditions of heat & cold, body deviate outside
the normal range of 36.1 to 37.8OC (97-100OF)
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The Transfer of Body Heat
Conduction Transfer of heat from one material to another through
direct molecular contact
Convection Transferring heat from one place to another by the motion
of gas or a liquid across the heated surface
Radiation
Primary method for discharging the body excess heat atrest
Evaporation Primary avenue for heat dissipation during exercise
80% during exercise, 20% at rest
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Balance of Body Heat Gain & Loss
Metabolic Heat Radiation
+ +
Environmental Heat Conduction+
Convection
+
Evaporation
Heat Gain Heat Loss
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Humidity & Heat Loss
The water vapor content humidity
When humidity is high, the air already containsmany water molecules.Thus, high humidity
limits sweat evaporation & heat loss Low humidity offers ideal opportunity for sweat
evaporation & heat loss (problem if waterevaporates from the skin more rapidly than
sweat is produced, the skin cab become toodry)
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Humidity & Heat Loss
Exposure to dry desert air at 32.2OC with 10%relative humidity, compared to the same airtemperature with 90% relative humidity
At 10% - you sweat profusely, but evaporationoccurs so rapidly that you not aware you aresweating
At 90% - little sweat can evaporate, continuous
bath of sweat, very little heat is removed
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Control of Heat Exchange
Internal body temperature (rectal) at rest - 37OC
(99OF)
During exercise exceed 40O
C
The Hypothalamus: Your Thermostat The hypothalamus houses your thermoregulatory
center It acted like a thermostat, monitoring your
temperature & accelerating heat loss or heatproduction as needed
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HypothermiaLow body temperature stimulates
thermoreceptors
(Impulse go to hypothalamus)
Vasoconstriction occurs in skin blood vessels, so less heatis lost across the skin
Skeletal muscle are activated, causing shivering, which increases
metabolism & generates heat
Body temperature increases
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HyperthermiaHigh body temperature stimulates
thermoreceptors
(Impulse go to hypothalamus)
Vasodilation occurs in skin blood vessels, so more heatis lost across the skin
Sweat glands become more active, increasing
evaporative heat loss
Body temperature decreases
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Effectors that Alter Body Temperature
Sweat glands Secrete sweat that moisten the skin
Smooth muscle around arterioles
Hot - dilate Skeletal muscle
Cold involuntary muscle contraction
Endocrine glands
Cooling the body stimulates thyroxin release Elevated metabolic rate
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Physiological Response to
Exercise in Heat CV Function
During exercise in heat, the heat loss mechanisms
complete with active muscle for more of the limitedblood volume. Thus neither area is adequately
supplied under extreme conditions
Q may remain constant, SV may decline, resulting in
a gradual upward drift in HR
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Physiological Response to
Exercise in Heat Energy Production O2 uptake also increases during exercise in heat
Body Fluid Balance: Sweating Sweating increases, lead to dehydration,& excessive
electrolyte loss
To compensate, the release of aldosterone & ADH,
causing sodium & water retention, which can expandthe plasma volume
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Measuring Heat Stress
Wet Bulb Globe Temperature (WBGT)
Dry bulb
Measures the actual air temperature
Wet bulb Keep moist
Black Bulb
Absorbs radiated heat
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Wet Bulb Globe Temperature (WBGT)
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Heat Related Disorders
Heat Stress
Reflected by air temperature, humidity, air velocity &
thermal radiation
Heat Cramps
Probably cause by losses of fluids & minerals that result
from excessive sweating
Heat Exhaustion
Inability of the CV system to adequately meet the needs of
active muscle & skin Heat Stroke
Cause by failure of the body,s thermoregulatory mechanism
Can be fatal if untreated
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Subjective Symptoms
Associated with Overheating
Rectal
Temperature
Symptoms
39.50C 40.50C Sensation over stomach & back withpiloerection goose bumps
40.50C 41.10C Muscular weakness, disorientation & loss of
postural equilibrium
41.10C 41.70C Diminished sweating, loss of consciousness &
hypothalamic control
> 42.20C Death R.I.P
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Prevention of Hyperthermia
Competition & practice outdoor should not be heldwhen WBGT is over 28OC
Scheduling practices either in early morning or at night
Fluid should be readily available
Athletes should be required to drink as much as theycan, stopping every 10 to 20 min for fluid break
Proper clothing wear as little as possible
Athletes should train adequately for fitness & become
heat acclimatized
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Heat Acclimatization
Athlete can adapt to heat by exercising in the
heat for up to an hour or more each day for 5
to 10 days
CV changes generally occur in the first 3 to 5days, but changes in sweating mechanism
generally take much longer (up to 10 days)
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Heat Acclimatization
Improvements
Rate of sweating increases
Reduce skin temperature, promote heat loss
SV increases
Aids the delivery of more blood to the active
muscle & skin
Reduce the rate of muscle glycogen use Delay onset of fatigue
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Exercise in the Cold
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Exercise in the Cold Our body avoid excessive cooling by:
Shivering
Involuntary muscle contraction increases metabolic heat
production
Nonshivering thermogenesis
Stimulation of the SNS & by the action of hormone (thyroxin
& catecholamines)
Peripheral vasoconstriction
Decrease the transfer of core heat to the skin, thus
decreasing heat loss to the environment
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Factors Affecting Body Heat Loss
Body size & composition
Small surface area to body mass ratio (children)&
those with more fat are less susceptible to
hypothermia
Female tolerance to cold better than men
Windchill
Wind increases heat loss by convention & conduction
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Physiological Responses to
Exercise in Cold
Muscle Function
Cooled muscle is weaken & fatigue occurs more rapidly
Muscle shortening velocity & power decreased
Metabolic Responses
During prolonged exercise in the cold, as energy supplies
diminish & exercise intensity declines, a person becomes
susceptible to hypothermia
Exercise triggers the release of catecholamines, whichincrease the mobilization & use of FFA for fuel. However,
in the cold, vasoconstriction impairs circulation to the
subcutaneous fat tissue, so this process is attenuated
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Health Risk During Exercise
in the Cold Hypothermia
Once the body temperature falls below 34.50C (940F), the
hypothalamus begin to lose ability to regulate body
temperature
29. 50
C total lost (associated with slowing of metabolicreaction drowsiness & coma)
Cardiorespiratory Effects
The heart SA node is primarily affected by hypothermia,
causing the HR to drop & reduce Q
Exposure to extreme cold does decrease respiratory rate &
volume
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Health Risk During Exercise
in the Cold Treatment of Hypothermia
Protection from cold
Provide dry clothing
Warm beverages
Slowing rewarming the victims
Frostbite Occurs as a consequence of the body attempts to prevent heat
loss
Vasoconstriction to the skin causes reduced BF & skin rapidlycools
Combined with the lack of oxygen & nutrients, causes the skintissue to die
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Frostbite
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Cold Acclimatization
Repeated exposure to the cold may alter
peripheral BF & skin temperature,
allowing greater cold tolerance