ACUTE COLD RESPONSES

1. ACUTE COLD RESPONSES

3. 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

4. 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

5. 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

6. 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

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

11. 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

12. 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.

17. 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

18. EXTERNAL HEAT LOSS WATER TEMPERATURE AND DURATION OF EXPOSURE

19. 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

20. EXTERNAL HEAT LOSSMORPHOLOGY AND MASS

21. 1. CONVECTIVE HEAT LOSS IS PROPORTIONAL TO BODY SURFACE AREA; INCREASED BSA, DECREASED CORE TEMPERATUREFOR 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

22. 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 DENSITYTHAN 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.

23. 3. SHAPE OF BODY ENDOMORHPIC (ROUND SHAPE) AND MESOMORPHIC (RECTANGULAR SHAPE) - BETTER COLD TOLERANCE ECTOMORPHIC (LINEAR SHAPE) - POORER COLD TOLERANCE

24. 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)

25. EXTERNAL HEAT LOSSSURFACE INSULATIONLAYER OF WATER ADHERES TO SKIN AT THE WATER-SKIN INTERFACE THAT PROVIDES AN INSULATORY EFFECT AGAINST CONVECTIVE (C) HEAT LOSS

26. 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

27. 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

28. 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?”

29. INTERNAL HEAT LOSS

30. 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

31. 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)

32. EXERCISE AND HEAT LOSS

33. EXERCISE AND HEAT LOSS

34. 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

35. FACTORS AFFECTING HEAT LOSS DURING EXERCISE

36. 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

37. 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 • NOTE: INCREASED BODY FAT = DECREASED HEAT LOSS

38. 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) OR GREATER BSA/BW RATIO IN THE UPPER EXTREMITIES (DEPENDS ON THE INDIVIDUAL)

39. 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

42. SOURCES OF HEAT GAIN

43. 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

44. 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

45. EXERCISE IN COLD AIR

46. 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

47. BODY FAT AND COLD AIR EXPOSURE

48. 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

49. 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)

50. EFFECTS OF COLD ON PERFORMANCE