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

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

Simultaneously accounts for conduction, convection, evaporation, and radiation.

Dry bulb measures air temperature (TDB).

Wet bulb measures temperature as water evaporates from it (TWB).

Black globe absorbs radiated heat (TG).

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

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

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).

Heat stroke is caused by failure of the body's thermoregulatory system.

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 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

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.

Amount of heat acclimatization depends on environmental conditions and duration of exposure and intensity of exercise.

Cardiovascular Respiratory System

xercise in the Heat:xercise in the Heat:Cardiovascular Demands Cardiovascular Demands

fig 7.6fig 7.6EE

A. Factors Affecting CV ResponseA. Factors Affecting CV Response1. 1. AcclimatizationAcclimatization - the adaptive changes - the adaptive changes

that occur when an individual that occur when an individual undergoes prolonged or repeated undergoes prolonged or repeated exposure to a stressful environment; exposure to a stressful environment; these changes reduce the physiological these changes reduce the physiological strain produced by such an environmentstrain produced by such an environment

Exercise in the Heat: Cardiovascular Demands Exercise in the Heat: Cardiovascular Demands

Cardiovascular Respiratory System

fig 7.8fig 7.8EE

2. Fitness Level2. Fitness Level3. Body Composition3. Body Composition4. Hydration Level4. Hydration Level

Exercise in the Heat: Cardiovascular Demands Exercise in the Heat: Cardiovascular Demands

Heat illnessHeat illness - a spectrum of - a spectrum of disorders that range in intensity disorders that range in intensity and severity from mild and severity from mild cardiovascular and central cardiovascular and central nervous system disruptions to nervous system disruptions to severe cell damage, including the severe cell damage, including the brain, kidney and liverbrain, kidney and liver

Exercise in the Heat:Exercise in the Heat:Cardiovascular Demands Cardiovascular Demands

1.1. Heat CrampsHeat Cramps - an acute disorder - an acute disorder consisting of brief, recurrent, and consisting of brief, recurrent, and excruciating pain in the voluntary muscles excruciating pain in the voluntary muscles of the legs, arms, or abdomenof the legs, arms, or abdomen

2.2. Heat SyncopeHeat Syncope - a temporary disorder - a temporary disorder characterized by circulatory failure due to characterized by circulatory failure due to pooling of blood in the peripheral veins pooling of blood in the peripheral veins and the subsequent decrease in and the subsequent decrease in ventricular filling, which leads to a ventricular filling, which leads to a decrease in cardiac outputdecrease in cardiac output

Exercise in the Heat:Exercise in the Heat:Cardiovascular Demands Cardiovascular Demands

3.3. Heat ExhaustionHeat Exhaustion - characterized by a - characterized by a rapid and weak pulse, fatigue, weakness, rapid and weak pulse, fatigue, weakness, profuse sweating, psychological profuse sweating, psychological disorientation, and faintingdisorientation, and fainting

4.4. Heat StrokeHeat Stroke - a serious medical - a serious medical emergency; it is characterized by emergency; it is characterized by elevated skin and core temperatures, elevated skin and core temperatures, tachycardia, vomiting, diarrhea, tachycardia, vomiting, diarrhea, hallucinations and comahallucinations and coma

Exercise in the Heat:Exercise in the Heat:Cardiovascular Demands Cardiovascular Demands

5.5. PreventionPrevention– Adequate time for acclimatizationAdequate time for acclimatization– Exercise during cooler timesExercise during cooler times– Avoid exercise if HIS indicates high Avoid exercise if HIS indicates high

riskrisk– Adequate hydration Adequate hydration priorprior to exercise to exercise

and replace fluid and replace fluid duringduring exercise exercise– Wear light color and loose fitting Wear light color and loose fitting

clothesclothes

Exercise in the Heat:Exercise in the Heat:Cardiovascular Demands Cardiovascular Demands