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).

Metabolic Responses to Exercise in the Heat Body temperature increases. Oxygen uptake increases. Glycogen depletion is hastened. w 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 w Air temperature w Humidity w Air velocity w Amount of thermal radiation

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

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

xercise in the Heat: Cardiovascular Demands 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