EXERCISE & SPORT IN THE COLD

Thermal Balance

Core temperature declines in the cold when heat loss exceeds heat production

Core temperature rises if heat gain exceeds heat loss

Humans can tolerate a decline in deep body temperature of 10°C but only an increase of 5°C (88F or 103F)

Long-term Cold Exposure

Hypothalamus acts as a thermostat Initiates the body’s heat-regulating

mechanisms: Thermal receptors in the skin Direct stimulation (detect change in

blood temp) Increases BMR, HR, respirations

Thermoregulation in Cold Stress: Heat Conservation & Production Stimulation of cutaneous cold

receptors constricts peripheral blood vessels, reducing the flow of warm blood to the body’s surface and redirecting it to the core

Epinephrine and norepinephrine increase heat production during cold exposure

Prolonged cold stress stimulates release of thyroxine (increases resting metabolism)

Heat loss

Circulation: At rest in the heat, heart rate and cardiac output increase while superficial arterial and venous blood vessels dilate to divert warm blood to the body shell

Evaporation: An effective thermal defense exists when evaporative cooling combines with a large cutaneous blood flow

Hormonal Adjustments: Sweating produces loss of water and electrolytes

Heat loss (cont.)

Why is it important to keep your head covered when out in the cold? No vasoconstrictor fibers to the head; therefore the head always remains unaltered

Temperature Regulation

Shivering Autonomic response to

falling core temperature Metabolic heat No work is done, almost

all energy contributes to generation of heat

Physical activity provides the greatest contribution in defending against cold

Core Temperature During Exercise Heat generated by active muscles

can raise core temperature to fever levels that would incapacitate a person if caused by external heat stress alone

Fatigue generally coincides with core temperatures between 100.4F/38C and 104/40°C, which impairs muscle activation directly from a high brain temperature that decreases the central drive to exercise

Exercise in the Cold

Core temperature becomes further compromised during chronic exertional fatigue and sleep loss, inadequate nourishment, reduced tissue insulation, and a depressed shivering heat production

Exercise energy metabolism sustains a constant core temperature in air as cold as -22°F

Exercise in the Cold

Wear several thin layers of clothing Add or remove during exercise as needed

CLO units = measure of insulation of clothing 1.0 clothing is ordinary business dress Should be comfortable at 70F N & S poles need 12 CLO

Sweating becomes an issue, especially when exercise is finished

Body Fat, Exercise, & Cold Stress Differences in body fat content

among individuals influence physiologic function in the cold during rest and exercise Successful ocean swimmers possess a

larger amount of subcutaneous fat than highly trained non-ocean swimmers; additional fat = insulation

Water Immersion

Water has 25% greater thermal conductivity than air & 350 times greater heat capacity than air

Greater the swimming intensity the colder the water.

Sensory deprivation tank: 92 F Learning to swim: 86 F Actively swimming: 80 F Competitive swimmers: 77F

Muscular Performance in Cold Every 2 degrees drop in F temp = 3%

drop in muscle power Normal skin temp: 91.4F

Extreme thermal discomfort < 77F Extremity temp:

73F = clumsiness 68F = impact on skin has to be 6x

greater than normal for usual sensation to be registered

59F = loss fine manipulative performance

Muscular Performance in Cold(cont.) Joint synovium becomes more

viscous creating stiffness Joints are needed in order to survive

If you are stranded, it’s not a bad idea to start walking to stay warm.

When fatigued, stopping to rest or eat/drink is detrimental Unable to generate enough heat & losses

are greater

Optimal Exercise Temps

Endurance on stationary bike = 52F Distance runners = 57F Climbers = anything above 0F

Cold Stress and Children

Large ratio of body surface area-to-mass is a liability during cold stress body heat dissipates rapidly

During exercise in the less stressful cold-air environment, children rely on: Augmented energy metabolism More effective peripheral vasoconstriction

in the limbs Brown fat = thermogenesis

Why more in kids?

Cold Stress and Children

A child’s distinctly large ratio of body surface area-to-mass facilitates heat loss in a warm environment but becomes a liability during cold stress because body heat dissipates rapidly

During exercise in the less stressful cold-air environment, children rely on: Augmented energy metabolism More effective peripheral vasoconstriction in the

limbs Brown fat = thermogenesis

Why more in kids?

Injuries from Cold

Frostbite Ice crystals form in skin Temp below 30.2F Recent studies suggest not to be too

aggressive in cuttin goff the black tissue Once “bit”, reoccurrence is easy Tissue is painful and hard, difficult to

heal Hypothermia Cold Shock

Frostbite

Predisposing factors to frostbite: Alcohol use vasodilator =

accelerated heat loss Low physical fitness Fatigue Dehydration Poor peripheral circulation

Susceptible areas: Face, ears, fingers/hands, feet/toes Tingling, numbness, burning

Injuries from Cold

Frostbite Hypothermia

Cold, water, wind Occur during any season Sense of cold & shiveringnumbness &

uncontrollable shiveringspeech slurs, thought process slowserratic mvmts, skin swells/blue unconsciousnessdeath

Cold Shock

Injuries from Cold

Frostbite Hypothermia Cold Shock

Ice cold water, fatal within 5-10 minutes 7 steps:

1. Peripheral vasoconstriction2. HR, CO3. systolic pressure4. Immediate hyperventilation5. muscular activity, inability to swim 100m6. breath/hold time7. Drowning, death by hypothermia uncommon

Survival times in water

Naked 30 min 1.0 CLO 60-80 min

5mm wet suit 120-150 min Dry suit 300 min

Acclimatization to Cold

Humans possess much less capacity for adaptation to long-term cold exposure than to prolonged heat exposure

Acclimatization to Cold (cont)

Cold adaptation occurs with regular, prolonged exposure Body regulates at a lower core temperature Repeated cold exposure of hands/feet

increases blood flow through these tissues Shivering occurs at a lower body

temperature Improved ability to sleep in the cold Changes in peripheral blood flow distribution 5 – 2 minute cold immersions will

reduce “cold shock” response by half

Wind-Chill Index

Air currents on a windy day magnify heat loss because the warmer insulating air layer surrounding the body continually exchanges with cooler ambient air

The wind-chill temperature index provides a useful way to understand the dangers from winter winds and freezing temperatures and provides frostbite threshold values