John W. Castellani, Ph.D.Thermal & Mountain Medicine Division

US Army Research Institute of Environmental MedicineNatick, MA 01760

john.castellani@us.army.mil

Prescribing Exercise for Cold-Weather Environments

Outline

How cold is it?Physiological responses to coldDoes cold change the FITT principle?Safety and prevention of cold injuriesCV disease & asthma

How cold is cold?

Ambient temperature

Wind Chill Temperature Index

National Weather Service, 2001

Immersion

Cold-Wet

•Behavioral ThermoregulationWear ClothingSeek ShelterUtilize Heat SourcesExercise

Protection Against the Cold

•Physiological Adjustments Vasoconstriction (Heat Conservation) Shivering (Heat Production)

S = M - (±W) ± R ± C ± K ± E

Gisolfi & Wenger

Cold

alpha-adrenergic mediated constriction

reduces cutaneous blood flow

lower skin temperature

lower skin to ambient temperature gradient

reduced heat loss

MRMEXMTG

EXM

MTG

TSK

SKIN

TSK

SKIN

C1 TC

TRUNK CORE

C2 TM

EXTREMITY CORE

ADJUSTABLE CIRCULATORY INSULATION

FIXED INSULATION FAT AND BODY STRUCTURE

ADJUSTABLE PERIPHERALCIRCULATORY INSULATION

FIXED INSULATION FAT AND BODY STRUCTURE

ADJUSTABLE SURFACE FILM INSULATION

ADJUSTABLE SURFACE FILM INSULATION

TA

TA

TC - TSK TSK - TA

MUSCLEBLOODFLOW

EX

TR

EM

ITIE

ST

RU

NK

AN

D

HE

AD

INSULATION

Lowering Of Peripheral Skin TemperaturesCauses Cold-induced Vasodilation

Time (min)

-5 0 5 10 15 20 25 30

Ski

n T

emp

erat

ure

(oC

)

0

5

10

15

20

40

Blo

od

Flo

w (

mV

)

0

500

1000

1500NailbedPadBlood Flow

O’Brien, J. Appl. Physiol., 2005

1500

Time (min)

0 30 60 90 120

50

100

150

200

#

ShiveringM

etab

oli

c H

eat

Pro

du

ctio

n (

W·m

-2)

Castellani et al., J. Appl.Physiol., 1998

Tcore = 35.8°CTskin = 21°C

0

2

4

6

8

10

12

14

16

REST SHIVERING12°C Tsk

35°C core

6 MPHJOG

MAXEXERCISE

ME

TS

Comparison Of Metabolic Costs

OX

YG

EN

UP

TA

KE

POWER OUTPUT

AMBIENT CONDITIONS

TEMPERATE

COLD

Shivering Is Related To Exercise Intensity

~ 60% VO2max

EXPOSURE TIME (min)

ST

RO

KE

VO

LU

ME

(L

)

Stroke Volume Increases During Cold Air Exposure (5°C)

Muza et al. , 1988

Oxygen Uptake (ml/min)

Hea

rt R

ate

(bp

m)

5.5°C

22.5°C

200 600 1000 1400

▲

▲

▲

▼

▼

▼

70

100

130

Hanna et al., 1975

Cold Vasoconstriction Increases TPR And BP

Epstein et al., NEJM, 1969

Increased Afterload And Increased Work Of Heart

Epstein et al., NEJM, 1969

Cold Acclimitization

Young, Handbook of Physiology, 1996

Young et. al, 1986

0 30 60 90

15

20

25

30

35

PRE-ACCLIMATIONPOST-ACCLIMATION

Cold Acclimation Effects On Skin Temperature

Sk

in t

em

pe

ratu

re (

°C)

Exposure Time (min)

Physiological Responses:

Modifiers

Individual-Related Factors

•Low Body Fat•Fatigue & Fitness•Dehydration•Age•Alcohol•Sleep Loss•Nicotine•Illness•Poor Nutrition•Poor Clothing/Equipment•Prior Cold Injury

FA

LL

IN

RE

CT

AL

TE

MP

ER

AT

UR

E (

°C)

MEAN SKINFOLD THICKNESS (mm-1)

20 10 56.7 4

Less Subcutaneous Fat = Greater Fall In Rectal Temperature

Keatinge, 1960

M [

W·m

-2 ]

VO2 max [ ml· min-1·kg-1 ]

1°C

.

Metabolic Rate During Cold Air ExposureAs A Function Of Physical Fitness

Bittel et. al, 1988

Tsk

[ °

C ]

VO2 max [ ml· min-1·kg-1 ]

1°C

.

Skin Temperature During Cold Air ExposureAs A Function Of Physical Fitness

Bittel et. al, 1988

TIME (MIN)

0 30 60 90 120

RE

CT

AL

TE

MP

ER

AT

UR

E (

OC

)

36.0

36.5

37.0

37.5 EUHYDRATION

HYPEROSMOTIC HYPOHYDRATION

ISOSMOTIC HYPOHYDRATION

O’Brien et al., J. Appl. Physiol. 1998

Dehydration has no effect on whole-body thermoregulation

Hypohydration & CIVD

Time (min)

0 10 20 30

Tem

per

atu

re (

oC

)

0

5

10

15

20

40

Pad

Nailbed

O’Brien & Montain, J. Appl. Physiol., 2003

euhydration

FIN

GE

R S

KIN

TE

MP

ER

AT

UR

E°C

IMMERSION DURATION, min

Aging Blunts The CIVD Response To Cold

0 5 10 15 20 25 30

4

5

6

7

8

9

10

11

12

13

14

15

16 61-70 yrs51-60 yrs41-50 yrs31-40 yrs20-30 yrs

Mathew et. al, 1986

Exercise Prescription

•Enhance physical fitness•Promote health by reducing risk for future development of disease•Ensure safety during participation in exercise

ACSM, Guidelines for Exercise Testing & Prescription, 4th Edition

Does Cold-Weather Affect How We Prescribe Exercise?

CardiovascularResistance ExerciseFlexibilitySafety of Participants

FrequencyIntensity

TimeTypeTo achieve

same HR at lowwork, need to work harder

Cardiovascular Conditioning

No change

No change

No change

Hea

rt R

ate

POWER OUTPUT

AMBIENT CONDITIONS

TEMPERATE

COLD

Heart Rate Related To Exercise Intensity?

??

Risk Reduction&

Prevention of Cold Injuries

Risk Management1. Identify

HazardHow cold is

it?5. Supervise

Evaluate & Correct Controls

2. Assess Hazards•Analyze Mission

Requirements•Determine Uniform &

Equipment•Identify High Risk

People

3. Develop Controls

Implement Cold

Mitigation

4. Implement ControlsAdopt &

Implement Controls into

Plans

Hypothermia Avoidance

Risk FactorsDecreased Heat ProductionTraining FactorsInactivityFatigueEnergy depletion

EndocrineHypopituitarismHypoadrenalismHypothyroidismHypoglycemiaDiabetes

Increased Heat LossEnvironmental FactorsImmersionRainWet clothing from sweatWind

ErythrodermasBurnsPsoriasisIcthyosisExfoliative dermatitisSunburn

IatrogenicEmergency birthCold infusionsHeat illness treatment

Impaired ThermoregulationPeripheral FailureTraumaNeuropathiesAcute spinal cord transection

Central Failure Central nervous system (CNS) lesions and traumaStrokeSubarachnoid hemorrhageHypothalamic dysfunctionParkinson’s DiseaseMultiple sclerosisPharmacologicToxicologicDrug and alcohol abuse

Miscellaneous Clinical StatesInfectionRenal failureCancer

Exercise in the Rain

Thompson & Hayward, 1996

Cold-Weather Clothing

Creating a microenvironment

Clothing Principles

• Insulation• Use loose layering to trap air• Keep clothing dry

• Ventilation• Avoid overheating• Evaporate moisture

• Environmental Protection• Windproof, waterproof

Layering & Fabrics

Inner layer – thin layer against the skin to wick moistureMid-layer – primary insulationOuter shell – windproof, waterproof, breathable

Limited vapor transfer rate; Use pit zips, side zips to ventilate

Cotton – absorbs moisture; heavy / bulky when wet; slow to dryWool – absorbs moisture; heavy / bulky when wet; coarse fibers

resist compression thus retain insulation when wetPolypropylene – fibers do not absorb any moisture - wicks by capillary action; lightweight; quick drying; melts in high heatPolyester – treated to be hydrophobic; wicks moisture; lightweight;

quick drying; melts in high heatNylon – absorbs moisture; wind resistant; quick dryingLeather – absorbs water, dries slowly. Treat for water repellency

Cold Weather Clothing System

Clothing Requirements

ISO, 1993

Temperature (°F)

-40 -20 0 20 40 60

Clo

thin

g In

sula

tion

(clo

)

0

1

2

3

4

5

6

7

8

9

10

1 Met

2 Mets

3 Mets

4 Mets

5 Mets

Example: 3 METS, 0°F, what clo needed?

No sweatRemove & add layersBe aware of weather changingKnow your athletes/clients limitsEncourage people to speak up

Keys to Working in Cold Weather

Frostbite Avoidance

Wind Chill Temperature Index

National Weather Service, 2001

Metabolic Rate (Watts)

200 220 240 260 280 300 320 340 360

Fin

ger

Tem

pera

ture

(°C

)

10

12

14

16

18

20

22

24

26

28No Wind

Wind @ 1 m·s-1

Wind @ 5 m·s-1

Mäkinen et al. Comp. Physiol. Biochem., 2001

Does finger respond to exercise in cold (-10°C)?

Dexterity Threshold

Ski

n T

emp

erat

ure

(°C

)

0

2

4

6

8

10

12

14

16

18Nose-no windNose - 1 m·s-1

Nose - 5 m·s-1

220 350

Metabolic Rate (Watts)

Does nose respond to exercise in cold (-10°C)?

Gavhed et al. Int. J. Biometerol., 2003

Caloric Requirements

10-40% higher (?)

Why?•Expend more energy - combination of clothing & equipment & terrain•Shivering if get cold enough

Castellani et al., USARIEM Technical Note 02-2

How in Cold?:•Sweating•Lower thirst•Cold-induced diuresis•Respiratory losses•Conscious under-drinking•Poor water availability

Dehydration Causes:•Decreases Physical Work Ability•Degrades Cognitive function•Reduces Appetite•Reduces Alertness•Constipation•Kidney Ailments•Urinary Infections

Dehydration

Clothing and the Cold

• Clothing provides a protective barrier (keeps cold out)

• Clothing also keeps heat in – but usually inhibits sweat evaporation

• Sweat losses of >1 L/hr are still common in very cold weather when heavily clothed (and therefore, dehydration is still a potential concern)

Monitoring Hydration

Watch out for:•Infrequent urination•Small volume of urine•Dark urine

Canteens and water containers can freezeCamelbacks are susceptible, esp. tubingDo not eat snow & ice (also watch out for potability)

Try to get warm beverages & hot meals during extended stays

Exercising in the Cold with Cardiovascular Disease

Mean % Increase in Mortality for each 1°C fall from 18°C air

0.0

0.5

1.0

1.5

2.0

2.5

SouthFinland

London Athens Palermo

EuroWinter Group, Lancet, 1997

Noble, Physiology 2004

How could the cold physiologically increase risk?

Coronary Blood Flow

Work of the Heart

Requirements for CBF

Reis et al., CHEST, 1998

% C

han

ge

-30

-20

-10

0

10

20

30

40

RatePressure Product

Coronary X-Sectional

Area

CoronaryBlood Flow

Change in Coronary Circulation After Cold Pressor Test

Change in Coronary Blood Blow?

Cold increases Rate Pressure Product

Brown & Oldridge, MSSE, 1985

144

157

-7.5°C air

Brown & Oldridge, MSSE, 1985

Cold decreases time to reach anginal threshold

7.8

6.1

-7.5°C air

100% of patientswith CAD hadan earlier onset of angina

Local Cooling

Neill et al. Am. J. Med., 1974

19 patients with CADAngina in 5 patientsMyocardial hypoxia in 7 patients

Facial Cooling

# o

f tr

ips

on

ste

ps

20

25

30

35

40

45

47°F air 73°F air 73°F air +ice cube

Ice Cube Holding

Friedman et al., Am. Heart J., 1944

Local Cooling

Exercise tolerance until angina onset

Patient Angina ST Dep.

HR Angina ST Dep.

HR

1 2 Yes 115 0 Yes 96

2 6 Yes 80 0 Yes 88

3 6 Yes 82 0 Yes 60

4 6 Yes 75 0 Yes 83

5 5 Yes 115 4 Yes 105

6 0 No - 0 No -

7 0 No - 0 No -

8 5 Yes 93 0 Yes 86

Supine Cycling Swimming (18°C)

Magder et al., Circulation, 1981

Swimming and Angina

Shoveling

Isometric ComponentValsalva ManeuverUpper Body Exercise

Sys

tolic

Blo

od

Pre

ssu

re

0

50

100

150

200

ME

TS

0

2

4

6

8

10

Treadmill ArmCrank

SnowShoveling

Snowblower

Cardiac Demands in Healthy People

Franklin et al., JAMA, 1995

Sheldahl et al., MSSE, 1993

Shoveling & Thermal Stressin Low-Risk

Cardiac Patients

Cold = -8°C (18°F)Neutral = 24°C (76°F)Warm = 29°C (85°F)

61% VO2peak

No ST depressionNo Angina

CV Disease - Summary

Increased mortality from CAD in winter, especially in hypertensivesWhole body cold exposure lowers anginal thresholdLocal cold exposure (face & hands) lowers anginal thresholdUse of HR as a marker of exercise intensity may be limitedCaution is warranted when swimming in cold pools or the oceanShoveling is safe if exercise intensity is kept low

CV Disease - Summary

Exercise Intensity

Rat

e P

ress

ure

Pro

du

ct (

HR

X S

BP

)

Cold

Warm

Anginal Threshold

Exercise Prescription

Lower Exercise IntensityLower Target Heart RateConsider Testing with Arm Ergometry (occupational tasks)Do Not Handle Cold Tools, Watch Out For SnowballsEducate About Clothing For Cold Weather Exercise

LayeringNo SweatingMinimize Facial Cooling

Consult Your Client’s Physician

Exercise-Induced Bronchoconstriction

- 3-10% Asymptomatic athletes- 70-80% Asthmatics

Narrowing of intrathoracic airwaysCold air enhances EIB vs. warm air

Giesbrecht, 1995; Zeitoun et al., 2004

Giesbrecht, Aviat. Space Environ. Med., 1995

•Airway smooth muscle contraction•Increased mucus production•Decreased mucociliary clearance•Vascular congestion•Epithelial damage and vascular leakage

Possible mechanisms for increased airways resistance

Facial Cooling

McFadden et al., 1997; Zeitoun et al., 2004

Skin & Head Cooling

Cold & Asthmatics

10.2% decrease

lower with facial cooling

Prevention of EIB

•Training/acclimatization (decrease in EIB in late winter)

•Wear heat/moisture exchanger•15-20 min. warm up•avoid polluted areas•follow physicians advice on medications

Information Sources

TB MED 508 Prevention And Management Of Cold Weather Injuries

Department of the Army, 2005www.usariem.army.mil

Prevention of Cold Injuries During ExerciseACSM Position Statement (in preparation)

Castellani, Young, Ducharme, Giesbrecht. Glickman, Sallis

“Man in a cold environment is not necessarily a cold man”

David Bass, 1958USARIEM Physiologist