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

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

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 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

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

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

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

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