Transcript Thermoregulation

Cardiovascular Exercise in the Heat
 Active muscles and skin compete for
blood supply.
 Stroke volume decreases.
 Heart rate gradually increases to
compensate for lower SV (cardiac drift).
Metabolic Responses to Exercise in the Heat
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Body temperature increases.
Oxygen uptake increases.
Glycogen depletion is hastened.
Muscle lactate levels increase.
Body Fluid and Exercise in the Heat
 Sweating increases.
 High volumes of sweat cause
• Blood volume to decrease,
• Loss of minerals and electrolytes,
and
• Release of aldosterone and ADH
and water reabsorption in kidneys.
EXERCISE IN HEAT AND COLD
Variables of Environment Heat Load
 Air temperature
 Humidity
 Air velocity
 Amount of thermal radiation
Wet Bulb Black Globe Temperature
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Simultaneously accounts for conduction,
convection, evaporation, and radiation.
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Dry bulb measures air temperature (TDB).
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Wet bulb measures temperature as water
evaporates from it (TWB).
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Black globe absorbs radiated heat (TG).
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WBGT = 0.1TDB + 0.7TWB + 0.2TG
WET BULB GLOBE
WARNING SIGNS OF HEAT
DISORDERS
Treatment of Heat Disorders
Heat cramps—move to cooler location and administer fluids
or saline solution
Heat exhaustion—move to cooler environment, elevate feet;
give saline if conscious or intravenous saline if
unconscious
Heat stroke—rapidly cool body in cold water, ice bath or with
wet towels; seek medical attention
Preventing Hyperthermia
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Avoid exercising in humid conditions above a
WBGT index of 28 °C (82.4 °F).
Schedule practices or events in early morning
or at night.
Wear light-weight, light-colored, loosely-woven
clothing.
Drink plenty of fluids.
Know the symptoms of heat stress.
Key Points : Heat Stress
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WBGT measures air temperature and accounts for
heat exchange via conduction, convection,
evaporation, and radiation.
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Heat cramps appear to be caused by loss of fluids
and minerals due to sweating.
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Heat exhaustion results from the cardiovascular
system being unable to meet the needs of muscles
and skin due to lower blood volume (from sweating).
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Heat stroke is caused by failure of the body's
thermoregulatory system.
Heat Acclimatization
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Ability to get rid of excess heat improves
Sweating becomes more efficient
Blood flow to skin is reduced; more blood is
available to muscles
Blood volume increases
Heart rate increase is less (than
nonacclimatized)
Stroke volume increases
Muscle glycogen usage decreases
HEAT ACCLIMATIZATION
You can achieve heat acclimatization by exercising in the
heat for 1 hour or more each day for 3 to 14 days.
Cardiovascular adaptations occur within the first 3 to 5
days while changes in sweating mechanisms may take
up to 14 days. Reduce exercise intensity to 60% to
70% the first few days before resuming more intense
workouts.
Heat Acclimatization
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Repeated exposure to heat stress during exercise
improves your ability to get rid of excess heat.
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Sweating increases in well-exposed areas to
promote heat loss.
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Stroke volume increases to aid in delivery of more
blood to the muscles and skin.
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Muscle glycogen use is reduced to delay onset of
fatigue.
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Amount of heat acclimatization depends on
environmental conditions and duration of exposure
and intensity of exercise.
xercise in the Heat:
Cardiovascular Demands
E
 fig 7.6
Cardiovascular Respiratory System
Exercise in the Heat: Cardiovascular Demands
A. Factors Affecting CV Response
1. Acclimatization - the adaptive changes
that occur when an individual
undergoes prolonged or repeated
exposure to a stressful environment;
these changes reduce the physiological
strain produced by such an environment
E
 fig 7.8
Cardiovascular Respiratory System
Exercise in the Heat: Cardiovascular Demands
2. Fitness Level
3. Body Composition
4. Hydration Level
Exercise in the Heat:
Cardiovascular Demands
 Heat illness - a spectrum of
disorders that range in intensity
and severity from mild
cardiovascular and central
nervous system disruptions to
severe cell damage, including the
brain, kidney and liver
Exercise in the Heat:
Cardiovascular Demands
1. Heat Cramps - an acute disorder
consisting of brief, recurrent, and
excruciating pain in the voluntary muscles
of the legs, arms, or abdomen
2. Heat Syncope - a temporary disorder
characterized by circulatory failure due to
pooling of blood in the peripheral veins
and the subsequent decrease in
ventricular filling, which leads to a
decrease in cardiac output
Exercise in the Heat:
Cardiovascular Demands
3. Heat Exhaustion - characterized by a
rapid and weak pulse, fatigue, weakness,
profuse sweating, psychological
disorientation, and fainting
4. Heat Stroke - a serious medical
emergency; it is characterized by
elevated skin and core temperatures,
tachycardia, vomiting, diarrhea,
hallucinations and coma
Exercise in the Heat:
Cardiovascular Demands
5. Prevention
– Adequate time for acclimatization
– Exercise during cooler times
– Avoid exercise if HIS indicates high
risk
– Adequate hydration prior to exercise
and replace fluid during exercise
– Wear light color and loose fitting
clothes