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Prescribing Exercise for Cold-Weather Environments. John W. Castellani, Ph.D. Thermal & Mountain Medicine Division US Army Research Institute of Environmental Medicine Natick, MA 01760 john.castellani@us.army.mil. Outline. How cold is it? Physiological responses to cold

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Prescribing Exercise for

Cold-Weather Environments

John W. Castellani, Ph.D.

Thermal & Mountain Medicine Division

US Army Research Institute of Environmental Medicine

Natick, MA 01760

john.castellani@us.army.mil


Outline

How cold is it?

Physiological responses to cold

Does cold change the FITT principle?

Safety and prevention of cold injuries

CV disease & asthma


How cold is cold?

Ambient temperature


Wind Chill Temperature Index

National Weather Service, 2001


Immersion


Cold-Wet


Protection Against the Cold

  • Physiological Adjustments

  • Vasoconstriction (Heat Conservation)

  • Shivering (Heat Production)

  • Behavioral Thermoregulation

  • Wear Clothing

  • Seek Shelter

  • Utilize Heat Sources

  • Exercise


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


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Lowering Of Peripheral Skin Temperatures

Causes Cold-induced Vasodilation

O’Brien, J. Appl. Physiol., 2005


Shivering

Metabolic Heat Production (W·m-2)

Tcore = 35.8°C

Tskin = 21°C

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


METS

REST

6 MPH

JOG

SHIVERING

12°C Tsk

35°C core

MAX

EXERCISE

Comparison Of Metabolic Costs


Shivering Is Related To Exercise Intensity

AMBIENT CONDITIONS

TEMPERATE

COLD

OXYGEN UPTAKE

~ 60% VO2max

POWER OUTPUT


Stroke Volume Increases During

Cold Air Exposure (5°C)

STROKE VOLUME (L)

EXPOSURE TIME (min)

Muza et al. , 1988


130

22.5°C

Heart Rate (bpm)

100

5.5°C

70

Oxygen Uptake (ml/min)

200

600

1000

1400

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


Cold Acclimation Effects On Skin Temperature

Skin temperature (°C)

Exposure Time (min)

Young et. al, 1986


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


Less Subcutaneous Fat = Greater Fall

In Rectal Temperature

FALL IN RECTAL TEMPERATURE (°C)

10

5

4

6.7

20

MEAN SKINFOLD THICKNESS (mm-1)

Keatinge, 1960


Metabolic Rate During Cold Air Exposure

As A Function Of Physical Fitness

1°C

M [ W·m-2 ]

.

VO2 max [ ml· min-1·kg-1 ]

Bittel et. al, 1988


Skin Temperature During Cold Air Exposure

As A Function Of Physical Fitness

1°C

Tsk [ °C]

.

VO2 max [ ml· min-1·kg-1 ]

Bittel et. al, 1988


Dehydration has no effect on

whole-body thermoregulation

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


Hypohydration & CIVD

euhydration

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


Aging Blunts The CIVD Response To Cold

FINGER SKIN TEMPERATURE

°C

IMMERSION DURATION, min

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?

Cardiovascular

Resistance Exercise

Flexibility

Safety of Participants


Cardiovascular Conditioning

No change

Frequency

Intensity

Time

Type

To achieve

same HR at low

work, need to work harder

No change

No change


Heart Rate Related To Exercise Intensity?

AMBIENT CONDITIONS

TEMPERATE

COLD

Heart Rate

??

POWER OUTPUT


Risk Reduction

&

Prevention of Cold Injuries


Risk Management

1. Identify Hazard

How cold is it?

  • 2. Assess Hazards

  • Analyze Mission Requirements

  • Determine Uniform & Equipment

  • Identify High Risk People

5. Supervise

Evaluate & Correct Controls

4. Implement Controls

Adopt & Implement Controls into Plans

3. Develop Controls

Implement Cold Mitigation


Hypothermia Avoidance


Risk Factors


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 moisture

Mid-layer – primary insulation

Outer shell – windproof, waterproof, breathable

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

Cotton – absorbs moisture; heavy / bulky when wet; slow to dry

Wool – absorbs moisture; heavy / bulky when wet; coarse fibers

resist compression thus retain insulation when wet

Polypropylene – fibers do not absorb any moisture - wicks by capillary action; lightweight; quick drying; melts in high heat

Polyester – treated to be hydrophobic; wicks moisture; lightweight; quick drying; melts in high heat

Nylon – absorbs moisture; wind resistant; quick drying

Leather – absorbs water, dries slowly. Treat for water repellency


Cold Weather Clothing System


Clothing Requirements

ISO, 1993


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


Keys to Working in Cold Weather

No sweat

Remove & add layers

Be aware of weather changing

Know your athletes/clients limits

Encourage people to speak up


Frostbite Avoidance


Wind Chill Temperature Index

National Weather Service, 2001


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

Dexterity Threshold

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


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


Dehydration

  • 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


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)

Clothing and the Cold


Monitoring Hydration

  • Watch out for:

  • Infrequent urination

  • Small volume of urine

  • Dark urine

Canteens and water containers can freeze

Camelbacks are susceptible, esp. tubing

Do 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


EuroWinter Group, Lancet, 1997


How could the cold physiologically increase risk?

Coronary

Blood Flow

Work of the Heart

Requirements for CBF

Noble, Physiology 2004


Change in Coronary Blood Blow?

Change in Coronary Circulation After Cold Pressor Test

Reis et al., CHEST, 1998


Cold increases Rate Pressure Product

-7.5°C air

157

144

Brown & Oldridge, MSSE, 1985


-7.5°C air

7.8

6.1

Cold decreases time to reach anginal threshold

100% of patients

with CAD had

an earlier onset

of angina

Brown & Oldridge, MSSE, 1985


Local Cooling

Facial Cooling

19 patients with CAD

Angina in 5 patients

Myocardial hypoxia in 7 patients

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


Local Cooling

Ice Cube Holding

Exercise tolerance until angina onset

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


Swimming and Angina

Supine Cycling

Swimming (18°C)

Magder et al., Circulation, 1981


Shoveling

Isometric Component

Valsalva Maneuver

Upper Body Exercise


Cardiac Demands in Healthy People

Franklin et al., JAMA, 1995


Shoveling & Thermal Stress

in Low-Risk

Cardiac Patients

Cold = -8°C (18°F)

Neutral = 24°C (76°F)

Warm = 29°C (85°F)

No ST depression

No Angina

61% VO2peak

Sheldahl et al., MSSE, 1993


CV Disease - Summary

  • Increased mortality from CAD in winter,

    especially in hypertensives

  • Whole body cold exposure lowers anginal threshold

  • Local cold exposure (face & hands)

    lowers anginal threshold

  • Use of HR as a marker of exercise intensity

    may be limited

  • Caution is warranted when swimming in cold pools

    or the ocean

  • Shoveling is safe if exercise intensity is kept low


CV Disease - Summary

Cold

Rate Pressure Product (HR X SBP)

Anginal Threshold

Warm

Exercise Intensity


Exercise Prescription

  • Lower Exercise Intensity

  • Lower Target Heart Rate

  • Consider Testing with Arm Ergometry (occupational tasks)

  • Do Not Handle Cold Tools, Watch Out For Snowballs

  • Educate About Clothing For Cold Weather Exercise

  • Layering

  • No Sweating

  • Minimize Facial Cooling

  • Consult Your Client’s Physician


Exercise-Induced Bronchoconstriction

Narrowing of intrathoracic airways

Cold air enhances EIB vs. warm air

  • - 3-10% Asymptomatic athletes

  • 70-80% Asthmatics

Giesbrecht, 1995; Zeitoun et al., 2004


Possible mechanisms for

increased airways resistance

  • Airway smooth muscle contraction

  • Increased mucus production

  • Decreased mucociliary clearance

  • Vascular congestion

  • Epithelial damage and vascular leakage

Giesbrecht, Aviat. Space Environ. Med., 1995


Cold & Asthmatics

Skin & Head Cooling

Facial Cooling

lower with facial cooling

10.2% decrease

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


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, 2005

www.usariem.army.mil

Prevention of Cold Injuries During Exercise

ACSM Position Statement (in preparation)

Castellani, Young, Ducharme, Giesbrecht. Glickman, Sallis


“Man in a cold environment

is not necessarily a cold man”

David Bass, 1958

USARIEM Physiologist


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