Post on 29-Mar-2015
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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