Test 8: Exercise in Hot & Cold - Thermoregulation

Core Temp

Core Temp

97-100*F

Temps above ______ can affect the nervous system and reduce the ability to unload excess heat

40*C

Conduction

transfer of hear from one solid material to another through direct molecular contact

Convection

moving heat from one place to another by the motion of gas or liquid across a heated surface

Radiation

• heat is given off in the form of infrared rays

• about 60% of heat loss at rest

Evaporation

heat is lost when fluid evaporates

What mode of “wet” heat transfer is the primary avenue for heat dissipation during exercise?

evaporation

Evaporation accounts for ____ of heat lost during exercise vs ____ at rest

• 80%

• 10-20%

Heat Balance Equation

M-W ± R ± C ± K - E = 0

Humidity

• water vapor pressure

• high humidity limits sweat evaporation

Effectors

• smooth muscle around arterioles

• “eccrine” sweat glands

• skeletal muscles

• endocrine glands

Cardiovascular drift

upward shift in HR compensates for blood in the periphery

Heat Stress & Health Risk Variables

• metabolic heat production

• air temp

• humidity

• air velocity

• radiant heat sources

• clothing

Wet-Bulb Glob Temp measures

conduction, convection, evaporation, and radiation

Heat Cramps

• severe and painful cramping of large muscle groups

• cause: by sodium losses and dehydration

• prevention: proper hydration and liberally salt food

• treatment: move to cooler location, fluids

Heat exhaustion

• extreme fatigue, dizziness, nausea, vomiting, fainting, rapid pulse

• cause: dehydration, decreased blood volume, sodium depletion

• treatment: move to cooler location, fluids, elevate feet

Heat Stroke

• increase in internal body temp, cessation of sweating, rapid pulse and respiration, confusion, unconsciousness

• cause: failure of the body’s thermoregulatory system

• treatment: rapidly cool body in cold water/ice bath/wet towels

Achieving Heat Acclimation

• exercise in heat for 1 hour or more for 9-14 days

• cardiovascular changes generally occur first

• plasma volume expands in 1-3 days

• changes in sweating takes up to 10 days or more

Cold Acclimation

• cold habituation

• metabolic adaption

• insulative acclimation

Factors that affect body heat loss

• body size and composition

• air temp

• windchill

• water immersion

Heat loss in cold water

• water has 26 times greater thermal conductivity

• total heat loss is 4 times faster

• heat transfer is accelerated if water is moving around individual

Exercise in the Cold Key Points

• peripheral vasocontstriction then non-shivering thermogenesis then shivering increases metabolic heat production

• increased surface area, decreased muscle mass, and decreased subcutaneous fat facilitate the loss of body heat to the environment

• immersion in cold water tremendously increases heat loss through convection

• wind/flowing water increases heat loss by convection

Physiological Responses

• muscle is cooled = less able to produce force and fatigue occurs more rapidly

• during prolonged exercise in cold, people become more susceptible to hypothermia

• exercise triggers the release of catecholamines - increase mobilization and use of FFA for fuel

• vasoconstriction impairs circulation to subcutaneous fat tissue

Hypothermia

• body core temp below 94.1*F

• HR drops

• decreased respiratory rate and volume

Frostbite

• exposed skin can freeze quickly when air temp < 0*C

Exercise Induced Asthma

drying of the airways

Health Risks during exercise in the cold

• The hypothalamus begins to lose its ability to regulate body temperature below 34.5 °C (94.1 °F)

• Hypothermia critically affects the heart’s SA node, decreasing heart rate and cardiac output

• Breathing cold air does not freeze the respiratory passages or lungs when ventilation is low

• Exposure to extreme cold decreases respiratory rate and volume

• Frostbite occurs as a consequence of the body’s attempts to prevent heat loss and can lead to tissue necrosis