1. ADAPTATIONS TO THE COLD

2. 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)

5. 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

7. 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

9. THE GREATER NON-FATTY (I. E
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

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

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

13. 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

14. 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)

16. 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%

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

18. 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

20. 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

22. 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

23. 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

24. 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

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

27. 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

31. 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

32. 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

33. 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

35. COLD ADAPTATIONS AND THE CARDIOVASCULAR AND RESPIRATORY SYSTEMS

36. 1. TENDS TO DECREASE THE PRESS. RESPONSE (BLOOD PRESSURE
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

37. 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

38. 3. NO EFFECT ON EXPIRED. VENTILATION RATE,. RESPIRATION RATE, AND
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

39. SUMMARY OF METABOLIC, HYPOTHERMIC, AND INSULATIVE ADAPTATIONS

40. METABOLIC • INCREASED BASAL OR RESTING METABOLIC RATE
• INCREASED HEAT PRODUCTION

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

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

43. PHYSICAL TRAINING AND COLD TOLERANCE

44. 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

45. 5. PHYSICAL TRAINING MAY. INCREASE OR DECREASE SKIN
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

46. B. IF SKIN TEMPERATUR DECREASES. AFTER TRAINING, THERMAL
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

47. 6. TRAINING IN COLD WATER. IMPROVES COLD TOLERANCE
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

48. B. IN ADDITION TO INSULATIVE. ADAPTATIONS, COLD WATER
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)

50. QUESTIONS?

51. THANK YOU!!