Thermal Regulation & Exercise

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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

Thermal Regulation & Exercise

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