john w. castellani, ph.d. thermal & mountain medicine division us army research institute of...
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John W. Castellani, Ph.D.Thermal & Mountain Medicine Division
US Army Research Institute of Environmental MedicineNatick, MA 01760
Prescribing Exercise for Cold-Weather Environments
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Outline
How cold is it?Physiological responses to coldDoes cold change the FITT principle?Safety and prevention of cold injuriesCV disease & asthma
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How cold is cold?
Ambient temperature
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Wind Chill Temperature Index
National Weather Service, 2001
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Immersion
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Cold-Wet
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•Behavioral ThermoregulationWear ClothingSeek ShelterUtilize Heat SourcesExercise
Protection Against the Cold
•Physiological Adjustments Vasoconstriction (Heat Conservation) Shivering (Heat Production)
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S = M - (±W) ± R ± C ± K ± E
Gisolfi & Wenger
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Cold
alpha-adrenergic mediated constriction
reduces cutaneous blood flow
lower skin temperature
lower skin to ambient temperature gradient
reduced heat loss
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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
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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
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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
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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
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OX
YG
EN
UP
TA
KE
POWER OUTPUT
AMBIENT CONDITIONS
TEMPERATE
COLD
Shivering Is Related To Exercise Intensity
~ 60% VO2max
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EXPOSURE TIME (min)
ST
RO
KE
VO
LU
ME
(L
)
Stroke Volume Increases During Cold Air Exposure (5°C)
Muza et al. , 1988
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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
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Cold Vasoconstriction Increases TPR And BP
Epstein et al., NEJM, 1969
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Increased Afterload And Increased Work Of Heart
Epstein et al., NEJM, 1969
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Cold Acclimitization
Young, Handbook of Physiology, 1996
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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)
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Physiological Responses:
Modifiers
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Individual-Related Factors
•Low Body Fat•Fatigue & Fitness•Dehydration•Age•Alcohol•Sleep Loss•Nicotine•Illness•Poor Nutrition•Poor Clothing/Equipment•Prior Cold Injury
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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
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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
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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
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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
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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
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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
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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
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Does Cold-Weather Affect How We Prescribe Exercise?
CardiovascularResistance ExerciseFlexibilitySafety of Participants
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FrequencyIntensity
TimeTypeTo achieve
same HR at lowwork, need to work harder
Cardiovascular Conditioning
No change
No change
No change
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Hea
rt R
ate
POWER OUTPUT
AMBIENT CONDITIONS
TEMPERATE
COLD
Heart Rate Related To Exercise Intensity?
??
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Risk Reduction&
Prevention of Cold Injuries
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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
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Hypothermia Avoidance
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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
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Exercise in the Rain
Thompson & Hayward, 1996
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Cold-Weather Clothing
Creating a microenvironment
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Clothing Principles
• Insulation• Use loose layering to trap air• Keep clothing dry
• Ventilation• Avoid overheating• Evaporate moisture
• Environmental Protection• Windproof, waterproof
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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
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Cold Weather Clothing System
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Clothing Requirements
ISO, 1993
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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?
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No sweatRemove & add layersBe aware of weather changingKnow your athletes/clients limitsEncourage people to speak up
Keys to Working in Cold Weather
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Frostbite Avoidance
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Wind Chill Temperature Index
National Weather Service, 2001
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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
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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
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Caloric Requirements
10-40% higher (?)
Why?•Expend more energy - combination of clothing & equipment & terrain•Shivering if get cold enough
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Castellani et al., USARIEM Technical Note 02-2
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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
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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)
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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
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Exercising in the Cold with Cardiovascular Disease
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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
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Noble, Physiology 2004
How could the cold physiologically increase risk?
Coronary Blood Flow
Work of the Heart
Requirements for CBF
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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?
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Cold increases Rate Pressure Product
Brown & Oldridge, MSSE, 1985
144
157
-7.5°C air
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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
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Local Cooling
Neill et al. Am. J. Med., 1974
19 patients with CADAngina in 5 patientsMyocardial hypoxia in 7 patients
Facial Cooling
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# 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
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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
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Shoveling
Isometric ComponentValsalva ManeuverUpper Body Exercise
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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
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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
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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
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CV Disease - Summary
Exercise Intensity
Rat
e P
ress
ure
Pro
du
ct (
HR
X S
BP
)
Cold
Warm
Anginal Threshold
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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
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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
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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
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Facial Cooling
McFadden et al., 1997; Zeitoun et al., 2004
Skin & Head Cooling
Cold & Asthmatics
10.2% decrease
lower with facial cooling
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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
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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
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“Man in a cold environment is not necessarily a cold man”
David Bass, 1958USARIEM Physiologist