1. Exercise & sport in the cold

3. 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)

4. 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

5. 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)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. Body Fat, Exercise, & Cold Stress
The physiologic strain from cold- water and cold-land environments depends on one’s level of metabolism and body fat’s resistance to heat flow

15. 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

16. 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

17. Optimal Exercise Temps
Endurance on stationary bike = 52F
Distance runners = 57F
Climbers = anything above 0F

18. 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?

19. 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?

20. Injuries from Cold Frostbite Hypothermia Cold Shock
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

21. Frostbite Predisposing factors to frostbite: Susceptible areas:
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

22. Injuries from Cold Frostbite Hypothermia Cold Shock Cold, water, wind
Occur during any season
Sense of cold & shiveringnumbness & uncontrollable shiveringspeech slurs, thought process slowserratic mvmts, skin swells/blue unconsciousnessdeath
Cold Shock

23. Injuries from Cold Frostbite Hypothermia Cold Shock
Ice cold water, fatal within 5-10 minutes
7 steps:
Peripheral vasoconstriction
 HR, CO
 systolic pressure
Immediate hyperventilation
 muscular activity, inability to swim 100m
 breath/hold time
Drowning, death by hypothermia uncommon

24. Survival times in water
Naked  30 min
1.0 CLO  min
5mm wet suit  min
Dry suit  300 min

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

26. 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

27. 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