ADAPTATIONS TO THE COLD

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ADAPTATIONS TO THE COLD
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• ACCLIMATIZATION ADAPTATIONS RESULTING FROM
  NATURAL CHANGES
• IN THE ENVIRONMENT (REVIEW FIGURES)
• ACCLIMATION - ADAPTATIONS INDUCED BY AN UNUSUAL
  ALTERATION OF THE ENVIRONMENT
• HABITUATION - DESENSITIZATION OR DAMPENING OF A
  NORMAL RESPONSE TO A STRESSOR (REVIEW FIGURE)

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• DECREASE IN SKIN TEMPERATURE IS GREATER THAN
  DECREASE IN CORE TEMPERATURE WHICH REFLECTS
• DECREASED HEAT CONDUCTANCE DUE TO
  COUNTER-CURRENT HEAT EXCHANGE AND/OR
  VASOCONSTRICTION

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• INSULATION - TENDENCY OF AN INDIVIDUAL TO RESIST
  LOSS OF BODY HEAT TO THE ENVIRONMENT TISSUE
  INSULATION IS DIRECTLY RELATED TO FAT MASS AND
  LEAN BODY MASS INSULATION WHICH INCREASES WITH
  COLD ADAPTATION (REVIEW FIGURE)
• TOTAL BODY INSULATION
• SUPERFICIAL SHELL - SKIN AND SUBCUTANEOUS
  FAT
• MUSCLE LAYER AND DEEPER BODY FAT

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• THE GREATER NON-FATTY (I.E., MUSCLE) SHELL
  INSULATION IS DUE TO INCREASED COUNTER-CURRENT
  HEAT EXCHANGE AND/OR DECREASED CORE TEMPERATURE
  THRESHOLD FOR ONSET OF SHIVERING AND/OR INCREASED
  VASOCONSTRICTION

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• CONDUCTANCE - TENDENCY OF AN INDIVIDUAL TO LOSE
  BODY HEAT TO THE ENVIRONMENT THERMAL CONDUCTANCE
  IS INVERSELY RELATED TO FAT MASS (REVIEW FIGURE)

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ADAPTATIONS TO THE COLD

• COLD ADAPTIVE PROCESSES TEND TO OCCUR IN THE
  FOLLOWING ORDER
• 1. METABOLIC
• 2. HYPOTHERMIC
• 3. INSULATIVE

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• GENERAL
• 1. ADAPTATIONS TO THE COLD TEND TO BE A FUNCTION
  OF THE PHYSIOLOGICAL STRESS INDUCED BY THE
  DURATION, FREQUENCY, AND INTENSITY OF THE COLD
  EXPOSURE
• 2. CHANGES IN SYMPATHETIC NERVOUS SYSTEM ACTIVITY
  MAY, IN PART, BE UNDERLYING THE OBSERVED
  ADAPTATION PROCESS
• REMEMBER ACUTE COLD EXPOSURE STIMULATES THE SNS
  RESULTING IN AN INCREASE IN THE CIRCULATING
  LEVELS OF NOREPINEPHRINE

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• METABOLIC ADAPTATIONS
• INCREASED BASAL METABOLIC RATE AND METABOLIC HEAT
  PRODUCTION DUE TO
• 1. INCREASED SHIVERING (?)
• IF IN FACT INCREASED SHIVERING OCCURS, IT
  APPEARS TO BE RELATED TO INCREASED SHIVERING
  CAPACITY AS THRESHOLD FOR THE ONSET OF
  SHIVERING IS DECREASED RATHER THAN INCREASED
  AFTER HYPOTHERMIC AND INSULATIVE ADAPTATIONS
  (REVIEW FIGURE)

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• 2. INCREASED NON-SHIVERING THERMOGENESIS
• A. INCREASED METABOLISM IN
  BROWN ADIPOSE TISSUE
• B. INCREASED SNS ACTIVITY
  (INCREASED NOREPINEPHRINE
• RELEASED)
• C. INCREASED THYROXIN RELEASED
• NOTE CHEMICAL THERMOGENSIS
• (B C) INCREASES HEAT
  PRODUCTION BY 10-15

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HYPOTHERMIC ADAPTATIONS

• 1. DECREASED METABOLIC HEAT PRODUCTION AND CORE
  TEMPERATURE
• 2. SKIN TEMPERATURE DOES NOT CHANGE OR
  INCREASES SLIGHTLY

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• THESE ADAPTATIONS MAY BE DUE TO
• 1. ACCLIMATION
• A. CIRCULATORY ADJUSTMENT THAT DIRECTED
  BLOOD FLOW FROM CORE TO PERIPHERAL VESSELS
  THEREBY KEEPING EXTREMITIES WARM WITHOUT
  INCREASED METABOLIC HEAT PRODUCTION (REVIEW
  FIGURE)
• NOTE ESKIMOS ALSO SHOW A HABITUATION RESPONSE
  (DAMPENING OF INITIAL RESPONSE) AS THEY HAVE LESS
  OF AN INITIAL VASOCONSTRICTION RESPONSE TO COLD
  EXPOSURE

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• AND/OR
• 2. HABITUATION
• A. DECREASED SET POINT FOR THE ONSET OF
  SHIVERING THEREFORE, MAINTENANCE OF SKIN
  TEMPERATURE WITH DECREASED METABOLIC HEAT
  PRODUCTION RESULTED IN THE OBSERVED DECREASE
  IN CORE TEMPERATURE (REVIEW FIGURE)
• B. DECREASED SNS AND NOREPINEPHRINE RELEASE
  IN RESPONSE TO COLD EXPOSURE
• DECREASED NON-SHIVERING
  THERMOGENESIS
• DECREASED VASOCONSTRICTION OF SUBCUTANEOUS
  VASCULATURE AND HENCE INCREASED
  VASODILATION

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• INSULATIVE ADAPTATIONS
• 1. BOTH CORE AND SKIN TEMPERATURES DECREASE
• 2. DECREASE IN CORE TEMPERATURE DUE TO A
  DECREASE IN SHIVERING THERMOGENESIS LOWER
  CORE TEMPEATURE THRESHOLD FOR THE ONSET OF
  SHIVERING

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• 3. DECREASED SKIN TEMPERATURE (WHICH DECREASES
  HEAT LOSS GRADIENT FROM SKIN SURFACE TO
  ENVIRONMEMT) DUE TO
• A. LOWER THERMAL CONDUCTIVITY OF
  METABOLIC HEAT AS SHIVERING
  THERMOGENESIS IS REDUCED, WHICH INCREASES
  INSULATIVE EFFECT OF LBW
• B. INCREASED VASOCONSTRICTION AS
  INCREASED SNS ACTIVITY
• INCREASES CIRCULATING LEVELS OF
  NOREPINEPHRINE WHICH REDUCES SKIN BLOOD
  FLOW DUE VASOCONSTRICTION
• C. DEVELOPMENT OF COUNTER-CURRENT HEAT
  EXCHANGE MECHANISMS

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• ABORIGINES COMPARED TO EUROPEAN CONTROL GROUP
  HAD
• - LOWER RESTING METABOLIC RATE
• - LOWER SKN TEMPERATURE (Tsk)
• - LOWER CORE TEMPERATURE (Tc)
• - LOWER CONDUCTANCE AS DECREASE IN Tc IS
  LESS THAN DECREASE IN Tsk MAY BE DUE TO
  ENHANCED VASOCONSTRICTION OR COUNTER- CURRENT
  HEAT EXCHANGE
• REVIEW FIGURE

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• DECREASE IN SKIN TEMPERATURE WAS GREATER THAN
  DECREASE IN CORE TEMPERATURE THEREFORE, THERMAL
  GRADIENT BETWEEN THE CORE AND SUBCUTANEOUS MUSCLE
  SHELL WAS INCREASED

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• HOWEVER, ENHANCED INSULATION OF THE SUPERFICIAL
  SHELL DUE TO GREATER CUTANEOUS VASOCONSTRICTION,
  WHICH WOULD LIMIT HEAT LOSS FROM THE MUSCLE SHELL
  RESULTING IN A WARMER AND BETTER PERFUSED MUSCLE
  SHELL IN THE COLD,
• OR INCREASED COUNTER-CURRENT HEAT EXCHANGE
• NOTE DECREASED SKIN TEMPERATURE MAKES SKIN
  TEMPERATURE CLOSER TO AIR OR WATER TEMPERATURE
  THEREBY INCREASING INSULATION AND DECREASING HEAT
  LOSS TO THE ENVIRONMENT
• REVIEW FIGURES

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SUMMARY COMMENTS REGARDING INSULATIVE ADAPTATIONS

• DECREASE IN SKIN TEMPERATURE IS GREATER THAN
  DECREASE IN CORE TEMPERATURE WHICH INCREASES
  THERMAL GRADIENT BETWEEN CORE AND MUSCLE SHELL
  PROVIDING PROTECTION TO MUSCLE SHELL

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SUMMARY COMMENTS REGARDING INSULATIVE ADAPTATIONS

• INCREASED VASOCONSTRICTION AND/OR INCREASED
  COUNTER-CURRENT HEAT EXCHANGE WILL DECREASE HEAT
  TRANSFER FROM MUSCLE SHELL TO SKIN SURFACE AND
  ENVIRONMENTAL SURROUNDINGS

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• COLD ADAPTATIONS
• AND BODY FLUID REGULATION
• MINIMAL EFFECTS ON BODY FLUID REGULATION AS THE
  MAGNITUDE OF PLASMA VOLUME REDUCTION INDUCED BY
  COLD EXPOSURE APPEARS TO BE UNAFFECTED BY COLD
  ACCLIMATION
• REVIEW FIGURE

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COLD ADAPTATIONS AND THE CARDIOVASCULAR AND
RESPIRATORY SYSTEMS
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• 1. TENDS TO DECREASE THE PRESS RESPONSE
  (BLOOD PRESSURE INCREASES WITH ACUTE COLD
  EXPOSURE) DUE TO HABITUATION OR INCREASED
  PERFUSION OF VASCULAR BEDS IN SKELETAL MUSCLE
  (ASSOCIATED WITH INSULATIVE ADAPTATIONS)
• REMEMBER DECREASED PERFUSION IS INITIALLY
  INDUCED WITH ACUTE COLD EXPOSURE

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• 2. NO EFFECT ON HEART RATE AND CARDIAC OUTPUT
• REMEMBER MAXIMAL HEART RATE AND CARDIAC OUTPUT
  ARE REDUCED IN THE COLD SUBMAXIMAL HEART RATE IS
  ELEVATED DUE TO SHIVERING THERMOGENESIS AND/OR
  INCREASED SNS ACTIVITY

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• 3. NO EFFECT ON EXPIRED VENTILATION RATE,
  RESPIRATION RATE, AND TIDAL VOLUME
• REMEMBER EXPIRED VENTILATION RATE IS INCREASED
  IN THE COLD DUE INCREASED RESPIRATION RATE AND/OR
  TIDAL VOLUME

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SUMMARY OF METABOLIC, HYPOTHERMIC, AND INSULATIVE
ADAPTATIONS
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METABOLIC

• INCREASED BASAL OR RESTING METABOLIC RATE
• INCREASED HEAT PRODUCTION

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HYPOTHERMIC

• DECREASED BASAL OR RESTING METABOLIC RATE
• DECREASED HEAT PRODUCTION
• DECREASED CORE TEMPERATURE
• NO CHANGE OR SLIGHT INCREASE IN SKIN TEMPERATURE

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INSULATIVE

• DECREASED BASAL OR RESTING METABOLIC RATE
• DECREASD HEAT PRODUCTION
• DECREASED CORE TEMPERATURE
• DECREASED SKIN TEMPERATURE
• DECREASED HEAT LOSS TO THE ENVIRONMENT

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PHYSICAL TRAINING AND COLD TOLERANCE
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• THRESHOLD FOR ONSET OF SHIVERING DURING COLD
  EXPOSURE IS DECREASED BY PHYSICAL TRAINING (I.E.,
  LOWER CORE TEMPERATURE BEFORE ONSET OF SHIVERING)
• DECREASED METABOLIC RATE AND RELATIVE EXERCISE
  INTENSIY (VO2max)
• DECREASED GLYCOGEN DEPLETION AND LACTATE
  PRODUCTION
• INCREASED WORK TIME TO EXHAUSTION

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• 5. PHYSICAL TRAINING MAY INCREASE OR DECREASE
  SKIN TEMPERATURE DURING COLD EXPOSURE
• A. IF SKIN BLOOD FLOW AND SKIN
  TEMPERATURE INCREASE AFTER TRAINING,
  METABOLIC RATE WOULD HAVE TO INCREASE TO
  MAINTAIN CORE TEMPERATURE

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• B. IF SKIN TEMPERATUR DECREASES AFTER
  TRAINING, THERMAL GRADIENT BETWEEN SKIN
  SURFACE AND ENVIRONMENT WOULD DECREASE AND
  THERMAL GRADIENT BETWEEN CORE AND SKIN
  WOULD INCREASE THEREBY FACILITATING THE
  TRANSFER OF HEAT FROM THE CORE TO THE
  SUBCUTANEOUS MUSCLE SHELL (INSULATIVE
  EFFECT)
• C. MORE RESEARCH IS NEEDED TO CLARIFY ISSUE

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• 6. TRAINING IN COLD WATER IMPROVES COLD
  TOLERANCE MORE THAN TRAINING IN COLD AIR
• A. HEAT LOSS TO COLD WATER IS FOUR
  TIMES GREATER THAN HEAT LOSS TO AIR
  THEREFORE, INTENSITY OF COLD EXPOSURE IS
  MUCH GREATER IN COLD WATER COMPARED TO COLD
  AIR

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• B. IN ADDITION TO INSULATIVE ADAPTATIONS,
  COLD WATER TRAINING MAY PREVENT THE
• LOSS OF SUBCUTANEOUS FAT TYPICALLY
  OBSERVED WITH TRAINING (I.E., SWIMMERS TEND
• TO RETAIN SUBCUTANEOUS FAT TO A GREATER
  EXTENT THAN OTHER ATHLETES TRAINING AT A
  SIMILAR LEVEL IN THE AIR)

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QUESTIONS?
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• THANK YOU!!