ADAPTATIONS TO THE COLD
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)
DECREASE IN SKIN
TEMPERATURE IS
GREATER THAN
DECREASE IN CORE
TEMPERATURE
WHICH REFLECTS
DECREASED HEAT
CONDUCTANCE DUE
TO COUNTERCURRENT HEAT
EXCHANGE AND/OR
VASOCONSTRICTION
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
THE GREATER NONFATTY (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
CONDUCTANCE - TENDENCY OF AN
INDIVIDUAL TO LOSE BODY HEAT TO
THE ENVIRONMENT; THERMAL
CONDUCTANCE IS INVERSELY
RELATED TO FAT MASS (REVIEW
FIGURE)
ADAPTATIONS TO THE COLD
COLD ADAPTIVE PROCESSES TEND TO
OCCUR IN THE FOLLOWING ORDER:
1. METABOLIC
2. HYPOTHERMIC
3. INSULATIVE
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
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)
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
HYPOTHERMIC ADAPTATIONS
1.DECREASED METABOLIC HEAT
PRODUCTION AND CORE
TEMPERATURE
2.SKIN TEMPERATURE DOES
NOT CHANGE OR INCREASES
SLIGHTLY
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
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
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
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
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
DECREASE IN SKIN TEMPERATURE
WAS GREATER THAN DECREASE IN
CORE TEMPERATURE;
THEREFORE, THERMAL GRADIENT
BETWEEN THE CORE AND
SUBCUTANEOUS MUSCLE SHELL
WAS INCREASED
• 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
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
SUMMARY COMMENTS REGARDING
INSULATIVE ADAPTATIONS
• INCREASED VASOCONSTRICTION
AND/OR INCREASED COUNTERCURRENT HEAT EXCHANGE WILL
DECREASE HEAT TRANSFER FROM
MUSCLE SHELL TO SKIN SURFACE
AND ENVIRONMENTAL
SURROUNDINGS
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
COLD ADAPTATIONS AND
THE
CARDIOVASCULAR
AND RESPIRATORY
SYSTEMS
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
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
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
SUMMARY OF METABOLIC, HYPOTHERMIC,
AND INSULATIVE ADAPTATIONS
METABOLIC
• INCREASED BASAL OR RESTING
METABOLIC RATE
• INCREASED HEAT PRODUCTION
HYPOTHERMIC
• DECREASED BASAL OR RESTING
METABOLIC RATE
• DECREASED HEAT PRODUCTION
• DECREASED CORE TEMPERATURE
• NO CHANGE OR SLIGHT INCREASE IN
SKIN TEMPERATURE
INSULATIVE
• DECREASED BASAL OR RESTING
METABOLIC RATE
• DECREASD HEAT PRODUCTION
• DECREASED CORE TEMPERATURE
• DECREASED SKIN TEMPERATURE
• DECREASED HEAT LOSS TO THE
ENVIRONMENT
PHYSICAL TRAINING AND COLD
TOLERANCE
1.
THRESHOLD FOR ONSET OF SHIVERING
DURING COLD EXPOSURE IS DECREASED BY
PHYSICAL TRAINING (I.E., LOWER CORE
TEMPERATURE BEFORE ONSET OF
SHIVERING)
2.
DECREASED METABOLIC RATE AND
RELATIVE EXERCISE INTENSIY
(%VO2max)
3.
DECREASED GLYCOGEN DEPLETION AND
LACTATE PRODUCTION
4.
INCREASED WORK TIME TO EXHAUSTION
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
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
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
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)
QUESTIONS?
THANK YOU!!