ACUTE COLD RESPONSES
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
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
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
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
• INCREASE IN METABOLIC RATE (HEAT
CONSERVATION MECHANISM) MAY NOT
BE ENOUGH TO MAINTAIN OR OFFSET
HEAT LOSS WHEN TEMPERATURE
FALLS BELOW CRITICAL TEMPERATURE
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
• 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.
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.
B.
REGIONAL HEAT FLOW
BODY FATNESS
EXTERNAL HEAT LOSS
WATER TEMPERATURE
AND DURATION OF
EXPOSURE
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
EXTERNAL HEAT LOSS
MORPHOLOGY AND MASS
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
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.
3.
SHAPE OF BODY
ENDOMORHPIC (ROUND SHAPE) AND
MESOMORPHIC (RECTANGULAR SHAPE)
- BETTER COLD TOLERANCE
ECTOMORPHIC (LINEAR SHAPE) - POORER
COLD TOLERANCE
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)
EXTERNAL HEAT LOSS
SURFACE INSULATION
LAYER OF WATER ADHERES TO SKIN AT
THE WATER-SKIN INTERFACE THAT
PROVIDES AN INSULATORY EFFECT
AGAINST CONVECTIVE (C) HEAT LOSS
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
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
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?”
INTERNAL HEAT LOSS
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
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)
EXERCISE AND HEAT LOSS
EXERCISE AND HEAT LOSS
EXERCISE IN AIR, CORE TEMPERATURE
CAN BE SUSTAINE D
IN TEMPERATURES
AS
LOW AS -30 oC
IN COLD H2 O, HEAT LOW IS 2 -4 TIMES GREATER;
AND MOVEMENT
THUS, THE PRESENCE
OF H2 O
OF H2 O FROM EXERCISE MAY INCREASE HEAT LOSS AND
DECREASE TC AS HEAT PRODUCTION
LOSS FROM CONVECTION
FROM EXERCISE
IS LESS THAN THE HEAT
• 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
FACTORS AFFECTING
HEAT LOSS DURING
EXERCISE
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.
4.
INCREASED HEAT PRODUCTION IN THE
EXTREMITIES VERSUS TRUNK WHEN
COMPARED TO NON-EXERCISING
CONDITION
INCREASED MOVEMENT OF
EXTREMITIES WILL DECREASE
INSULATORY BOUNDARY OF WATER AT
SKIN-WATER INTERFACE
THE
5. 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
6. NOTE: INCREASED BODY FAT =
DECREASED HEAT LOSS
6. 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)
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
SOURCES OF HEAT GAIN
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
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
EXERCISE IN COLD AIR
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
BODY FAT AND COLD AIR
EXPOSURE
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
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)
EFFECTS OF COLD ON
PERFORMANCE
1.CARDIORESPIRATORY
ENDURANCE
2.STRENGTH AND POWER
3.MUSCULAR ENDURANCE
CARDIORESPIRATORY
ENDURANCE
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
C. 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
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
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
C. DECREASED RELEASE OF OXYGEN
FROM HEMOGLOBIN TO MUSCLE
TISSUE
D. DECREASED PLASMA VOLUME WHICH
DECREASES OXYGEN TRANSPORT TO
THE MUSCLE TISSUE
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
STRENGTH AND POWER
1.REDUCED STRENGTH (PEAK
TORQUE), PARTICULARLY AT
FASTER VELOCITIES
2.DECREASED PERFORMANCE IN
POWER, SPRINTING, AND
JUMPING EVENTS
MECHANISMS:
1.
2.
3.
4.
5.
INCREASED TIME FOR MUSCLE TO
REACH PEAK (MAXIMAL) TENSION
THE RATE AT WHICH CROSSBRIDGES
FROM MYOSIN BREAK AND REATTACH TO
ACTIN IS DECREASED (SLOWS DOWN)
INCREASED FLUID VISCOSITY IN
SARCOPLASM INCREASES THE
RESISTANCE TO MOVEMENT OF THE
CROSSBRIDGES AND ACTIN
ENZYMES AND CHEMICAL
REACTIONS SLOW DOWN AND ATP
UTILIZATION DECREASES AT LOW
MUSCLE TEMPERATURES
NERVE CONDUCTION DECREASES
AND MOTOR UNIT RECRUITMENT
PATTERNS ARE IMPAIRED
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
COLD TOLERANCE IN OLDER ADULTS
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
DRESSING FOR WINTER
EXERCISE
1. REVIEW HAND-OUT
ON DRESSING
FOR WINTER EXERCISE
2. REVIEW PREVIOUS
LECTURE MATERIAL FROM
EARLIER IN THE
SEMESTER REGARDING
FACTORS THAT AFFECT
THE INSULATIVE VALUE OF
CLOTHING
3. COMMENTS
REGARDING CLOTHING
FOR COLDER CLIMATES
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
3.
MIDDLE LAYER SHOULD TRAP AIR
GOOSE DOWN
POLYESTER
POLYOLEFRIN
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
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
COLD INJURIES
COLD EXPOSURE RISKS
• KNOW THE SYMPTOMS,
CONTRIBUTING FACTORS,
TREATMENT, AND PRECAUTIONS
FOR FROSTBITE, HYPOTHERMIA,
EXERCISE-INDUCED
BRONCHOSPASM, AND
DEHYDRATION SUMMARIZED ON
THE HAND-OUT