Cardiovascular Exercise in the Heat

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Cardiovascular Exercise in the Heat

• Active muscles and skin compete for blood supply.
• Stroke volume decreases.
• w Heart rate gradually increases to compensate
  for lower SV (cardiac drift).

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Metabolic Responses to Exercise in the Heat

• Body temperature increases.
• Oxygen uptake increases.
• Glycogen depletion is hastened.
• w Muscle lactate levels increase.

3
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.

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EXERCISE IN HEAT AND COLD
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Variables of Environment Heat Load

• w Air temperature
• w Humidity
• w Air velocity
• w Amount of thermal radiation

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Wet Bulb Black Globe Temperature

• w Simultaneously accounts for conduction,
  convection, evaporation, and radiation.
• w Dry bulb measures air temperature (TDB).
• w Wet bulb measures temperature as water
  evaporates from it (TWB).
• w Black globe absorbs radiated heat (TG).
• w WBGT 0.1TDB 0.7TWB 0.2TG

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WET BULB GLOBE
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WARNING SIGNS OF HEAT DISORDERS
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Treatment of Heat Disorders

• Heat crampsmove to cooler location and
  administer fluids or saline solution
• Heat exhaustionmove to cooler environment,
  elevate feet give saline if conscious or
  intravenous saline if unconscious
• Heat strokerapidly cool body in cold water, ice
  bath or with wet towels seek medical attention

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Preventing Hyperthermia

• 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.
• w Know the symptoms of heat stress.

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Key Points Heat Stress

• WBGT measures air temperature and accounts for
  heat exchange via conduction, convection,
  evaporation, and radiation.
• Heat cramps appear to be caused by loss of fluids
  and minerals due to sweating.
• Heat exhaustion results from the cardiovascular
  system being unable to meet the needs of muscles
  and skin due to lower blood volume (from
  sweating).
• w Heat stroke is caused by failure of the body's
  thermoregulatory system.

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Heat Acclimatization

• 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
• w Muscle glycogen usage decreases

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HEAT ACCLIMATIZATION
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• 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.

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Heat Acclimatization

• Repeated exposure to heat stress during exercise
  improves your ability to get rid of excess heat.
• Sweating increases in well-exposed areas to
  promote heat loss.
• Stroke volume increases to aid in delivery of
  more blood to the muscles and skin.
• Muscle glycogen use is reduced to delay onset of
  fatigue.
• w Amount of heat acclimatization depends on
  environmental conditions and duration of exposure
  and intensity of exercise.

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xercise in the HeatCardiovascular Demands
E

• fig 7.6

Cardiovascular Respiratory System
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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

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E

• fig 7.8

Cardiovascular Respiratory System
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Exercise in the Heat Cardiovascular Demands

• 2. Fitness Level
• 3. Body Composition
• 4. Hydration Level

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Exercise in the HeatCardiovascular 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

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Exercise in the HeatCardiovascular 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

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Exercise in the HeatCardiovascular 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

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Exercise in the HeatCardiovascular 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