ACUTE COLD RESPONSES. GENERAL COMMENTS HEAT LOSS TO H 2 O IS 2-4X FASTER THAN AIR, ESPECIALLY DURING SWIMMING DUE TO INCREASED FORCED CONVECTIVE HEAT.

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 COMPOSITIONIncreased LBW will increase metabolism (1.3 Kcal/kg LBW/hr)

• STATE OF ENDOCRINE SYSTEMThyroxin, 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 metabolismCold 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 AIR2. 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 ANDDURATION OF

EXPOSUREB. MORPHOLOGY AND MASSC. SURFACE INSULATION

2. INTERNAL HEAT LOSS

A. REGIONAL HEAT FLOWB. 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 LOSSMORPHOLOGY 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 LOSSSURFACE 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 SUSTAINED IN TEMPERATURES AS

LOW AS -30oC

IN COLD H2O, HEAT LOW IS 2-4 TIMES GREATER; THUS, THE PRESENCE OF H2O

AND MOVEMENT OF H2O FROM EXERCISE MAY INCREASE HEAT LOSS AND

DECREASE TC AS HEAT PRODUCTION FROM EXERCISE IS LESS THAN THE HEAT

LOSS FROM CONVECTION

• 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. 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

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. INCREASED TIME FOR MUSCLE TO REACH PEAK (MAXIMAL) TENSION

2. THE RATE AT WHICH CROSSBRIDGES FROM MYOSIN BREAK AND

REATTACH TO ACTIN IS DECREASED (SLOWS DOWN)

3. INCREASED FLUID VISCOSITY IN SARCOPLASM INCREASES THE RESISTANCE TO MOVEMENT OF

THE CROSSBRIDGES AND ACTIN4. ENZYMES AND CHEMICAL

REACTIONS SLOW DOWN AND ATP UTILIZATION DECREASES AT LOW MUSCLE TEMPERATURES

5. 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-OUTON 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 AIRTRAPPED FOR INSULATION

B. OUTER LAYER SHOULD BE WIND AND WATER RESISTANT

GORTEX - WIND AND H2O RESISTANTLYCRA - 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 - ICHYCOTTON - 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