Factors Affecting Cold Stress
-Environmental (ambient) temperature
-Metabolism (people with lower metabolism and less muscle get colder)
-Resistance to heat loss provided by insulation
-subcutaneous adipose tissue
-muscle tissue (related to metabolic rate)
-clothing
Shivering�
rapid involuntary cycle of contraction and relaxation of muscles
Nonshivering thermogenesis�
stimulation of (increasing)metabolism
Peripheral vasoconstriction�
reduces blood flow to skin
Factors That Affect Body Heat Loss
- body size and composition
- air temperature
- wind chill
- water immersion
Responses to Exercise in the Cold:
Muscles _________ and _________ more rapidly
weaken and fatigue
Responses to Exercise in the Cold:
Susceptibility to hypothermia
increases
Responses to Exercise in the Cold:
Exercise-induced FFA mobilization is impaired due to
vasoconstriction of subcutaneous blood vessels
�Mild hypothermia:
core T drops to 90-95 F
-vasoconstriction, shivering, mental confusion, HR & RR increases
�Moderate hypothermia:
core T drops to 82-90 F
-violent shivering, impaired coordination, additional peripheral vasoconstriction, stumbling
�Severe hypothermia:
core T drops below 82 F
-cessation of shivering, difficulty with speech and cognitive function, cellular metabolism shuts down, HR & RR slow down, organ system failure, death
Ability to regulate body temperature is lost if Tbody drops below
34.5 �C (94.1�F).
Hypothermia causes heart rate to drop, which reduces
cardiac output.
Vasoconstriction in the skin reduces blood flow to skin, eventually causing __________.
frostbite
�Trench foot:
repetitive exposure to wet, but not freezing temps
�Frostnip:
superficial cooling of tissues without cell damage
�Chilblains:
superficial ulcers of the skin following repeated exposure to cold
�Frostbite:
freezing and cellular destruction of tissue
Alcohol causes vasodilation and increases
blood flow to skin accelerating heat loss
Initial adaptations to repeated periods of cold exposure lasting 30-60 min reduce
physiological stress and discomfort
Longer exposures from 3 hrs to 14 day blunt or delay
physiological response resulting in small reductions in core temp
Myth: "freezing your lungs
�Air is warmed and moisturized in the conducting zones of the lungs
�Cold air is usually dryer than warmer air and may dry out the airways
�Cold air can also irritate the airways
�Increased respiration can result in loss of heat during expiration
Strategies for exercising in the cold:
�Layer clothing and minimize
skin exposure
Strategies for exercising in the cold:
�Synthetic fabrics & wool provide good
insulation and dry quickly after getting wet
Strategies for exercising in the cold:
�Polyester fibers are good at
wicking away perspiration and minimizes heat loss when layered.
Strategies for exercising in the cold:
�Maintain hydration as cold, dry air dries out
mucous membranes and conducting zones.
Strategies for exercising in the cold:
�Airway masks can help retain moisture from
expired air, and prevent heat loss.
The cerebral cortex controls voluntary actions to
preserve heat
Catecholamine levels increase in blood and thyroid hormone levels
rise.