ACUTE COLD RESPONSES

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ACUTE COLD RESPONSES
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GENERAL COMMENTS

• HEAT LOSS TO H2O IS 2-4X FASTER THAN AIR,
  ESPECIALLY DURING SWIMMING DUE TO INCREASED
  FORCED CONVECTIVE HEAT LOSS
• THERMONEURTRALITY
• HEAT LOSS METABOLIC HEAT PRODUCTION

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FACTORS AFFECTING METABOLIC HEAT PRODUCTION

• BODY SIZE
• BODY COMPOSITION
• Increased LBW will increase metabolism (1.3
  Kcal/kg LBW/hr)
• STATE OF ENDOCRINE SYSTEM
• Thyroxin, epinephrine, norepinephrine
  stimulate metabolism

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FACTORS AFFECTING METABOLIC HEAT PRODUCTION

• AGE and GENDER
• RACE
• ACTIVITY
• FOOD CONSUMPTION
• ENVIRONMENT
• Heat will increase metabolism and reliance on
  anaerobic metabolism
• Cold will increase shivering thermogenesis

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CRITICAL TEMPERATURE

• TEMPERATURE BELOW WHICH ENERGY METABOLISM
  INCREASES ABOVE RESTING LEVEL (35o C IN LEAN
  PERSON, 30o C OR LESS IN FAT PERSON)
• CRITICAL TEMPERATURE IS INVERSELY RELATED TO
  SUBCUTANEOUS BODY FAT
• REVIEW FIGURES
• 1. CRITICAL TEMPERATURE HIGHER FOR H20 THAN
  AIR
• 2. GREATER VARIABILITY IN AIR THAN H20

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• INCREASE IN METABOLIC RATE (HEAT CONSERVATION
  MECHANISM) MAY NOT BE ENOUGH TO MAINTAIN OR
  OFFSET HEAT LOSS WHEN TEMPERATURE FALLS BELOW
  CRITICAL TEMPERATURE

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HEAT CONSERVATION MECHANISMS

• VASOCONSTRICTION
• SHIVERING METABOLISM
• - BOTH SUBMAXIMAL AND MAXIMAL SHIVERING VO2
  ARE HIGHLY CORRELATED TO VO2MAX
• - HIGHEST SHIVERING VO2 IS ABOUT 50 OF VO2MAX
• - VO2MAX AS A DETERMINANT OF THERMOGENESIS
  DURING SHIVERING MAY IN PART BE RELATED TO
  MUSCLE MASS AND/ OR THE SPECIFIC METABOLIC LEVEL
  ATTAINED BEFORE THE ONSET OF ANAEROBIC
  METABOLISM

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• REMEMBER SWEATING RATE, NUMBER OF DAYS TO
  ACCLIMATE, AND STEADY-STATE CORE TEMPERATURE WERE
  ALSO RELATED T O MAXIMAL OXYGEN UPTAKE RATE IN A
  HYPERTHERMIC ENVIRONMENT.

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• FACTORS CONTRIBUTING TO HEAT LOSS
• 1. EXTERNAL HEAT LOSS
• A. WATER TEMPERATURE AND DURATION OF
  EXPOSURE
• B. MORPHOLOGY AND MASS
• C. SURFACE INSULATION
• 2. INTERNAL HEAT LOSS
• A. REGIONAL HEAT FLOW
• B. BODY FATNESS

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EXTERNAL HEAT LOSS WATER TEMPERATURE AND DURATION
OF EXPOSURE
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• WATER TEMPERATURE RAPIDLY AND PROFOUNDLY AFFECTS
  THERMAL RESPONSES COMPARED TO AIR
• 1. DECREASE IN H20 TEMPERATURE WILL DECREASE
  CORE TEMPERATURE
• 2. INCREASE IN DURATION OF EXPOSURE WILL
  LOWER CORE TEMPERATURE, BUT NOT NECESSARILY
  LINEARLY AS CORE TEMPERATURE HAS BEEN SHOWN TO
  STABILIZE IN TEMPERATURES AS COLD AS 5o C

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EXTERNAL HEAT LOSSMORPHOLOGY AND MASS
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• 1. CONVECTIVE HEAT LOSS IS PROPORTIONAL TO
  BODY SURFACE AREA INCREASED BSA, DECREASED
  CORE TEMPERATURE FOR A GIVEN COLD EXPOSURE
• 2. ALSO, THE GREATER THE BSA TO BODY WEIGHT
  RATIO, THE GREATER THE DECREASE IN CORE
  TEMPERATURE FOR A GIVEN COLD EXPOSURE LOWER
  BSA/BW RATIO RESULTS IN A LOWER HEAT LOSS
  POTENTIAL

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• NOTE WHEN COMPARING INDIVIDUALS OF THE SAME
  BODY WEIGHT, THE PERSON WITH LESS BODY FAT (I.E.,
  LEAN PERSON) WILL HAVE A LOWER BSA TO BODY WEIGHT
  RATIO THAN A PERSON WITH MORE BODY FAT (I.E., FAT
  PERSON) SINCE FAT WEIGHT HAS A LOWER DENSITY THAN
  LEAN BODY WEIGHT. A FAT PERSON HAS A GREATER
  BSA/BW RATIO AND HENCE GREATER HEAT LOSS
  POTENTIAL IN A COLD TEMPERATURE THAN A LEAN
  PERSON, AT LEAST BASED ON THE BSA/BW RATIO.

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3. SHAPE OF BODY ENDOMORHPIC (ROUND SHAPE) AND
MESOMORPHIC (RECTANGULAR SHAPE) - BETTER COLD
TOLERANCE ECTOMORPHIC (LINEAR SHAPE) - POORER
COLD TOLERANCE
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4. BODY COMPOSITION GREATER LEAN BODY WEIGHT
INCREASED HEAT PRODUCTION LOWER BSA/BW
RATIO BOTH ENHANCE COLD TOLERANCE GREATER
FAT WEIGHT INCREASED INSULATION
(increased cold tolerance) GREATER BSA/BW
RATIO (decreased cold tolerance)
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EXTERNAL HEAT LOSSSURFACE INSULATION LAYER OF
WATER ADHERES TO SKIN AT THE WATER-SKIN INTERFACE
THAT PROVIDES AN INSULATORY EFFECT AGAINST
CONVECTIVE (C) HEAT LOSS

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• FACTORS AFFECTING INSULATORY EFFECT
• 1. WATER MOVEMENT WILL DECREASE INSULATION AND
  MAY INCREASE CONVECTIVE HEAT LOSS, ALTHOUGH
  THIS IN PART MAY BE OFFSET BY THE FACT THAT THE
  WATER MOVEMENT WILL LOWER SKIN TEMPERATURE AND
  THEREFORE DECREASE THE GRADIENT BETWEEN SKIN
  AND WATER TEMPERATURES

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• 2. DECREASE IN WATER TEMPERATURE WILL
  INCREASE OVERALL CONVECTIVE HEAT LOSS
• 3. EXERCISE TENDS TO INCREASE CONVECTIVE HEAT
  LOSS BY INCREASING HEAT LOSS BY FORCED
  CONVECTION (TURBULENT CIRCULATING MEDIUM)
  ALSO, EXERCISE TENDS TO REMOVE THE BOUNDARY
  LAYER OF INSULATORY WATER AS DISCUSSED UNDER 1
  ON THE PREVIOUS SLIDE

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• NOTE
• EXECISE ALSO DECREASES VAOCONSTRICTION DUE TO
  INCREASED VASODILATION, WHICH ALSO INCREASES
  CONVECTIVE HEAT LOSS
• EXERCISE HOWEVER INCREASES METABOLIC HEAT
  PRODUCTION
• IS THE INCREASE IN HEAT PRODUCTION GREATER THAN
  THE INCREASE IN HEAT LOSS WHEN EXERCISING OR
  MOVING IN THE WATER?

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INTERNAL HEAT LOSS
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• 1. REGIONAL HEAT FLOW
• VASOCONSTRICTION OF PERIPHERAL AND EXTREMITY
  VASCULATURE PREVENTS HEAT LOSS, WHICH
  DECREASES THE INTERNAL EFFECTIVE SURFACE
  AREA FOR HEAT TRANSFER
• HEAT FLOW VARIES WITHIN THE BODY
• AT REST, HEAT LOSS FROM THE
  ABDOMINAL/TRUNK AREA IS GREATER THAN FROM THE
  EXTREMITIES, PROBABLY DUE TO DECREASED BLOOD
  FLOW TO THE EXTREMITIES AREAS OF GREATEST HEAT
  LOSS ARE THE HEAD (50), NECK, LATERAL
  THORAX, UPPER CHEST, GROIN

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• 2. BODY FATNESS
• FAT PROVIDES A GREATER INSULATION THAN
  MUSCLE AND SKIN INCREASED CORE AND
  SUBCUTANEOUS FAT WILL INCREASE THE CONSERVATION
  OF HEAT
• HOWEVER, INCRESED LEAN BODY WEIGHT WILL
  INCREASE HEAT PRODUCTION (1.3 Kcal/kg LBW/hr)

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EXERCISE AND HEAT LOSS
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EXERCISE AND HEAT LOSS
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• EXERCISE IN AIR, CORE TEMPERATURE CAN BE
  SUSTAINED IN TEMPERATURES AS LOW AS -30o C (- 22o
  F)
• IN COLD WATER, HEAT LOSS IS 2-4 TIMES GREATER
  THUS, THE PRESENCE OF WATER AND MOVEMENT OF WATER
  FROM EXERCISE MAY INCREASE HEAT LOSS AND DECREASE
  CORE TEMPERATURE AS HEAT PRODUCTION FROM EXERCISE
  IS LESS THAN THE HEAT LOSS FROM CONVECTION

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FACTORS AFFECTING HEAT LOSS DURING EXERCISE
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• 1. INCREASED TRANSFER OF HEAT FROM THE TRUNK
  AND CORE TO THE EXTREMITIES VIA INCREASED BLOOD
  FLOW
• 2. INCREASED EFFECTIVE SURFACE AREA FOR HEAT
  TRANSFER AS BLOOD FLOW IS REDISTRIBUTED FROM
  THE TRUNK TO THE EXTREMITIES
• 3. INCREASED HEAT PRODUCTION IN THE
  EXTREMITIES VERSUS TRUNK WHEN COMPARED TO
  NON-EXERCISING CONDITION
• 4. INCREASED MOVEMENT OF EXTREMITIES WILL
  DECREASE INSULATORY BOUNDARY OF WATER AT THE
  SKIN-WATER INTERFACE

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1. SUBCUTANEOUS BODY FAT, PARTICULARLY IN THE
   EXTREMITIES AS BLOOD FLOW IS REDISTRIBUTED FROM
   THE TRUNK TO THE EXTREMITIES IN ELDERLY PEOPLE,
   THE TRANSLOCATION OF BODY FAT FROM THE
   EXTREMITIES TO THE ABDOMINAL/TRUNK AREA MAY MAKE
   THEM PARTICULARLY SUSCEPTIBLE TO HEAT LOSS IN
   COLD ENVIRONMENTS
2. NOTE INCREASED BODY FAT DECREASED HEAT
   LOSS

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• TYPE OF EXERCISE (REVIEW FIGURES)
• HEAT LOSS IS GREATER WITH ARM EXERCISE THAN LEG
  EXERCISE IN COLD TEMPERATURES DUE TO LESS
  EFFECTIVE CONSERVATION OF HEAT WITH ARM EXERCISE
  BECAUSE
• A. LESS INSULATION (I.E., LESS
  SUBCUTANEOUS FAT IN ARMS)
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• GREATER BSA/BW RATIO IN THE UPPER
  EXTREMITIES (DEPENDS ON THE INDIVIDUAL)

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• B. LEG EXERCISE MAY BE MORE EFFECTIVE IN
  TRANSFERRING HEAT PRODUCTION TO THE
  ABDOMINAL/TRUNK CORE
• C. IF PERFORMING THE SAME ABSOLUTE WORKLOAD,
  THE RELATIVE WORKLOAD IS GREATER DURING ARM
  EXERCISE (VO2MAX OF ARMS IS ABOUT 60-70 OF
  VO2MAX OF LEGS) THEREFORE, GREATER RATES OF
  BLOOD FLOW ARE NECESSARY AS EVIDENCED BY
  HIGHER HEART RATES DURING ARM EXERCISE

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SOURCES OF HEAT GAIN
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• 1. NON-SHIVERING THERMOGENESIS
• A. INCREASED RATE OF METABOLISM OF BROWN
  ADIPOSE TISSUE (?)
• B. CIRCULATING EFFECTS OF HORMONES
• COLD EXPOSURE STIMULATES THE SNS INCREASING
  CATECHOLAMINE RELEASE WHICH HAS A CALORIGENIC
  EFFECT, ESPECIALLY WHEN THYROXIN IS PRESENT
• IN AN UNADPATED PERSON, INCREASED
  GLUCOCORTICOID RELEASE IN THE COLD MAY INHIBIT
  THYROXIN RELEASE AND DECREASE THE CALORIGENIC
  EFFECT

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• 2. SHIVERING THERMOGENESIS
• DURING COLD EXPOSURE, SHIVERING MAY
  CONTRIBUTE UP TO 36 OF THE
• INCREASED HEAT LIBERATION
• 3. VASOCONSTRICTION OF THE CUTANEOUS
  VASCULATURE (NOREPINEPHRINE FROM THE SNS IS A
  STRONG VASOCONSTRICTOR) THUS, BLOOD IS
  SHUNTED TO THE CORE

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EXERCISE IN COLD AIR
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• 1. IN CONTRAST TO COLD WATER, EXERCISE IN
  COLD AIR ALWAYS INCREASES HEAT PRODUCTION
  ENOUGH TO MAINTAIN THERMAL BALANCE
• 2. REGULATES REGIONAL TEMPERATURE BY INCREASING
  BLOOD FLOW, WHICH DECREASES INJURY POTENTIAL,
  PARTICULARLY IN THE EXTREMITIES
• 3. ALTHOUGH HEAT LOSS VIA VENTILATION MAY
  INCREASE UP TO AS MUCH AS 9, THIS EXERTS
  MINIMAL AFFECT ON CORE TEMPERATURE

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BODY FAT AND COLD AIR EXPOSURE
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1. INCREASED BODY FAT PROTECTS FROM COLD
AIR INCREASED SUBCUTANEOUS FAT WILL
INCREASE INSULATION, PARTICULARLY IN EXTREMITIES
AND TRUNK/ABDOMEN CORE TEMPERATURE DURING
COLD AIR EXPOSURE TENDS TO BE LINEARLY RELATED
TO PERCENT BODY FAT
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• 2. SUBCUTANEOUS FAT REDUCES LOWERING OF CORE
  TEMPERATURE IN COLD AIR BY PROVIDING RESISTANCE
  OF HEAT TRANSFER FROM CORE TO SKIN BY
  CONDUCTION AND SKIN TO ENVIRONMENT BY
  CONVECTION
• ALSO, CONVECTION OF HEAT FROM THE SKIN TO
  ENVIRONMENT IS REDUCED BY THE DECREASE IN SKIN
  BLOOD FLOW DUE TO VASOCONSTRICTION OF THE
  PERIPHERAL VASCULATURE (TRUE FOR AIR AND
  WATER)

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EFFECTS OF COLD ON PERFORMANCE
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• 1. CARDIORESPIRATORY ENDURANCE
• 2. STRENGTH AND POWER
• 3. MUSCULAR ENDURANCE

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CARDIORESPIRATORY ENDURANCE
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• 1. REDUCED VO2MAX AND MAXIMAL EXERCISE
  PERFORMANCE
• A. DECREASED MAXIMAL HEART RATE AND HENCE,
  DECREASED CARDIAC OUTPUT
• B. HEMOGLOBN-O2 DISSOCIATION CURVE SHIFTS
  TO LEFT WHICH DECREASES THE AMOUNT
  OF O2 UNLOADED FROM HEMOGLOBIN
• AT THE MUSCLE TISSUE LEVEL AND
  HENCE, O2 EXTRACTION IS DECREASED

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• DECREASED PLASMA VOLUME WHICH DECREASES
• OXYGEN TRANSPORT TO THE MUSCLE TISSUE
• DECREASED PLASMA VOLUME DUE TO
• INCREASED DIURESIS
• SWEATING
• NOTE HYPOHYDRATION CAN OCCUR IN COLD
• AS WELL AS HOT ENVIRONMENTS AND
• HENCE, FLUID REPLACEMENT IS CRITICAL
• IN BOTH ENVIRONMENTS

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• 2. REDUCED SUBMAXIMAL EXERCISE PERFORMANCE AND
  AN EARLIER ONSET OF FATIGUE
• A. DECREASED CORE TEMPERATURE ELEVATES
  METABOLIC RATE
• (VO2) THUS REQUIRING A PERSON TO
  WORK AT A HIGHER PERCENT OF MAXIMAL
  OXYGEN UPTAKE RATE
• - GLYCOGEN DEPLETION
• - INCREASED LACTATE PRODUCTION,
  WHICH INTERFERES WITH
  CONTRACTILE PROCESSES

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• B. BLOOD FLOW TO MUSCLE TISSUE MAY BE REDUCED
  IN COLD, PARTICULARLY IN UNADAPTED PERSON
• - DECREASED O2 DELIVERY TO MUSCLE
  TISSUE AS RELEASE OF
  NOREPINEPHRINE FROM SNS CAUSES
  VASOCONSTRICTION
• - INCREASED RELIANCE ON
  ANAEROBIC ENERGY PRODUCTION
  AND HENCE, INCREASED BLOOD
  LACTATE PRODUCTION

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• DECREASED RELEASE OF OXYGEN FROM HEMOGLOBIN TO
  MUSCLE TISSUE
• DECREASED PLASMA VOLUME WHICH DECREASES OXYGEN
  TRANSPORT TO THE MUSCLE TISSUE

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• REMEMBER
• VO2 Q X O2 EXTRACTION
• Q SV X HR
• OXYGEN EXTRACTION ARTERIAL
  MINUS VENOUS OXYGEN DIFFERENCE
• V02 (SV X HR) X A - V 02 DIFFERENCE
• ALSO
• Q PRESSURE GRADIENT / RESISTANCE

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STRENGTH AND POWER

• 1. REDUCED STRENGTH (PEAK TORQUE), PARTICULARLY
  AT FASTER VELOCITIES
• 2. DECREASED PERFORMANCE IN POWER, SPRINTING,
  AND JUMPING EVENTS

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• MECHANISMS
• 1. INCREASED TIME FOR MUSCLE TO REACH PEAK
  (MAXIMAL) TENSION
• 2. THE RATE AT WHICH CROSSBRIDGES FROM MYOSIN
  BREAK AND REATTACH TO ACTIN IS DECREASED (SLOWS
  DOWN)
• 3. INCREASED FLUID VISCOSITY IN SARCOPLASM
  INCREASES THE RESISTANCE TO MOVEMENT OF THE
  CROSSBRIDGES AND ACTIN
• 4. ENZYMES AND CHEMICAL REACTIONS SLOW DOWN
  AND ATP UTILIZATION DECREASES AT LOW MUSCLE
  TEMPERATURES
• 5. NERVE CONDUCTION DECREASES AND MOTOR UNIT
  RECRUITMENT PATTERNS ARE IMPAIRED

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MUSCULAR ENDURANCE

• MUSCULAR ENDURANCE IS REDUCED BY THE COLD
  PRIMARILY DUE TO REDUCED NERVE CONDUCTION AND THE
  RECRUITMENT OF FEWER MOTOR UNITS (MUSCLE FIBERS),
  ESPECIALLY THOSE NEAREST THE MUSCLE SURFACE
• OTHER MECHANISMS DISCUSSED UNDER STRENGTH AND
  POWER MAY ALSO AFFECT MUSCULAR ENDURANCE AS
  MUSCULAR ENDURANCE IS RELATED TO STRENGTH

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COLD TOLERANCE IN OLDER ADULTS
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• IN ADDITION TO THE PREVIOUSLY DISCUSSED FACTORS
  RELATED TO AGING AND THERMOREGULATION, OLDER
  ADULTS HAVE POORER COLD TOLERANCE (I.E., LOWER
  CORE TEMPERATURE IN THE COLD) DUE TO
• DECREASED VASOCONSTRICTION IN RESPONSE TO THE
  COLD
• LESS OF AN INCREASE IN RMR IN RESPONSE TO THE
  COLD
• ALSO, LOSS OF MUSCLE MASS DUE TO AGING RESULTS
  IN A LOWER RMR
• LOWER RMR RESULTS IN LOWER METABOLIC HEAT
  PRODUCTION
• REDISTRIBUTION OF BODY FAT FROM EXTREMITIES TO
  ABDOMINAL AREA

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DRESSING FOR WINTER EXERCISE
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REVIEW HAND-OUTON DRESSING FOR WINTER EXERCISE
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2. REVIEW PREVIOUS LECTURE MATERIAL FROM EARLIER
IN THE SEMESTER REGARDING FACTORS THAT AFFECT THE
INSULATIVE VALUE OF CLOTHING
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3. COMMENTS REGARDING CLOTHING FOR COLDER CLIMATES
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• A. LAYER CLOTHING TO INCREASE THE AIR
• TRAPPED FOR INSULATION
• B. OUTER LAYER SHOULD BE WIND AND
• WATER RESISTANT
• GORTEX - WIND AND H2O RESISTANT
• LYCRA - WIND RESISTANT

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3. MIDDLE LAYER SHOULD TRAP AIR GOOSE
DOWN POLYESTER POLYOLEFRIN
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• D. INNER LAYER SHOULD WICK AWAY MOISTURE FROM
  THE SKIN AND PROTECT SKIN FROM THE COLD
• POLYPROPYLENE - HELPS RETAIN NEEDED BODY
  HEAT, BUT WILL PASS EXCESS BODY HEAT TO THE
  SURFACE
• SILK - EXPENSIVE AND LESS DURABLE
• WOOL - ICHY
• COTTON - COMFORTABLE AND DURABLE, WICKS AWAY
  SWEAT BUT DRIES SLOWLY

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• NOTES
• WET CLOTHING AND FATIGUE ARE TWO FACTORS WHICH
  GREATLY INCREASE THE RISK OF HYPOTHERMIA
• REMEMBER TO COVER THE HEAD AND TRUNK DURING
  PROLONGED COLD EXPOSURE

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COLD INJURIES
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COLD EXPOSURE RISKS

• KNOW THE SYMPTOMS, CONTRIBUTING FACTORS,
  TREATMENT, AND PRECAUTIONS FOR FROSTBITE,
  HYPOTHERMIA, EXERCISE-INDUCED BRONCHOSPASM, AND
  DEHYDRATION SUMMARIZED ON THE HAND-OUT

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