Exercise Physiology and Heat Tolerance
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What is the primary role of cardiac output during physical activity in hot weather?

  • To regulate skin temperature only
  • To lower stroke volume in response to heat stress
  • To decrease heart rate and conserve energy
  • To maintain thermal balance by increasing blood flow to the skin (correct)

    • Which factor does NOT modify heat tolerance during physical activity?

  • Acclimatization
  • Eye color (correct)
  • Body fat percentage
  • Age

    • What are the symptoms of heat exhaustion?

  • Excessive shivering and slow pulse
  • High body temperature and confusion
  • Intense thirst and muscle cramps
  • Extreme fatigue and nausea (correct)

    • What does the wind-chill temperature index primarily affect?

    <p>The perception of cold temperature on skin</p> Signup and view all the answers

    Which of the following is NOT a physical factor contributing to heat balance?

    <p>Emotional stress</p> Signup and view all the answers

    What is the core temperature range considered normal for humans?

    <p>36.1 - 37.8 ∘ C</p> Signup and view all the answers

    Which temperature increase is considered tolerable for the human body?

    <p>+5°C</p> Signup and view all the answers

    What does thermoregulation refer to?

    <p>The process of maintaining body temperature under diverse environmental conditions.</p> Signup and view all the answers

    Which measure is used to estimate the risk of heat stress?

    <p>Heat Stress Index</p> Signup and view all the answers

    What does the Wet Bulb Globe Temperature (WBGT) assess?

    <p>Thermal heat load imposed by the environment</p> Signup and view all the answers

    At what skin temperature would a human body likely be considered at risk of overheating?

    <p>33.3 ∘ C</p> Signup and view all the answers

    How does relative humidity influence the assessment of environmental temperature risk?

    <p>It is essential in estimating heat stress risk.</p> Signup and view all the answers

    How much can humans tolerate a decline in deep body temperature?

    <p>-10°C</p> Signup and view all the answers

    What is the primary physiological factor influencing gastric emptying?

    <p>Caloric content and volume of fluid consumed</p> Signup and view all the answers

    Which condition is indicated by a plasma sodium level less than 135 mmol/L?

    <p>Exercise-induced hyponatremia</p> Signup and view all the answers

    Which of the following best describes heat cramps?

    <p>Brief, recurrent pain in voluntary muscles</p> Signup and view all the answers

    What physiological change occurs during heat syncope?

    <p>Pooling of blood in the peripheral veins</p> Signup and view all the answers

    Which of the following symptoms is associated with heat exhaustion?

    <p>Rapid weak pulse and psychological disorientation</p> Signup and view all the answers

    What is the most serious outcome of exertional heat illness?

    <p>Heat stroke characterized by extreme body temperature</p> Signup and view all the answers

    What role does glucose play in intestinal absorption during physical activity?

    <p>Increases intestinal absorption</p> Signup and view all the answers

    Which condition represents a fatal consequence of extreme heat and exercise?

    <p>Heat stroke</p> Signup and view all the answers

    What is the first stage of hypothermia?

    <p>Body temperature drops to 35-34ºC</p> Signup and view all the answers

    What physiological change occurs during severe hypothermia?

    <p>Loss of reflexes and voluntary motion</p> Signup and view all the answers

    How does body fat influence cold stress?

    <p>Increases effective insulation in cold water</p> Signup and view all the answers

    At what body temperature does shivering cease in moderate hypothermia?

    <p>87.8ºF</p> Signup and view all the answers

    What is a common physiological change observed during mild hypothermia?

    <p>Increased blood pressure</p> Signup and view all the answers

    What happens to neuromuscular function during stage 2 of hypothermia?

    <p>It is affected</p> Signup and view all the answers

    When does the body start experiencing organ failure in hypothermia?

    <p>At below 32ºC</p> Signup and view all the answers

    Which group is likely to withstand cold stress better due to physical adaptations?

    <p>Successful ocean swimmers</p> Signup and view all the answers

    What condition is associated with body temperature at 25.0ºC?

    <p>Severe hypothermia</p> Signup and view all the answers

    What is a psychological response to exposure to extreme cold?

    <p>Behavior changes and confusion</p> Signup and view all the answers

    Which of the following best describes the physiological state at normothermia?

    <p>No noticeable effect occurs</p> Signup and view all the answers

    What can reduce tissue insulation during cold exposure?

    <p>Chronic exertional fatigue</p> Signup and view all the answers

    What is the primary physiological response to cold stress?

    <p>Increased metabolic rate</p> Signup and view all the answers

    Which behavioral change can help with acclimatization to cold environments?

    <p>Warm-up exercises</p> Signup and view all the answers

    Which of the following is NOT an adaptation to cold exposure?

    <p>Decreased piloerection</p> Signup and view all the answers

    What effect does exercise in a cold environment have on muscle performance?

    <p>Reduced force production</p> Signup and view all the answers

    What is a psychological adjustment one may experience during cold acclimatization?

    <p>Enhanced ability to endure cold</p> Signup and view all the answers

    Which response is associated with the body's sympathetic stimulation during cold stress?

    <p>Vasoconstriction</p> Signup and view all the answers

    Which adaptation occurs due to cold acclamation specifically related to high altitude exposure?

    <p>Vasodilation</p> Signup and view all the answers

    What is a likely consequence of exercise-induced asthma in cold environments?

    <p>Higher oxygen consumption</p> Signup and view all the answers

    What physiological change is likely to occur with prolonged cold exposure?

    <p>Increased sympathetic nervous activity</p> Signup and view all the answers

    Which factor is typically NOT a characteristic of cold stress during exercise?

    <p>Lower metabolic reliance on carbohydrates</p> Signup and view all the answers

    Which of the following is a sign of lowered body temperature?

    <p>Constant shivering</p> Signup and view all the answers

    What is a risk factor for cold injury?

    <p>Older age</p> Signup and view all the answers

    Chilblains typically occur due to repeated exposure to air temperatures in which range?

    <p>0-16°C</p> Signup and view all the answers

    Which area of the body is least susceptible to frostbite?

    <p>Forehead</p> Signup and view all the answers

    What is a characteristic of frostbite?

    <p>Inflamed tissue damage</p> Signup and view all the answers

    How does high wind speed affect the insulation value of clothing?

    <p>It disturbs the insulation zone.</p> Signup and view all the answers

    What is considered non-freezing cold stress?

    <p>Chilblains</p> Signup and view all the answers

    What effect does vigorous body movement have on thermal regulation?

    <p>It increases ventilation of air layers.</p> Signup and view all the answers

    Which of the following symptoms is NOT associated with lower body temperature?

    <p>Sharp mental clarity</p> Signup and view all the answers

    What is the primary risk associated with alcohol consumption in cold environments?

    <p>Decreased circulation</p> Signup and view all the answers

    What describes the condition known as frostnip?

    <p>Firm, cold, white area</p> Signup and view all the answers

    Which layer of clothing is effective at wicking moisture away from the skin?

    <p>Synthetic fibers</p> Signup and view all the answers

    Long-term exposure to which temperature range may lead to trench foot?

    <p>0-10°C</p> Signup and view all the answers

    Which action aids in maintaining body heat when wearing cold-weather clothing?

    <p>Limiting air movement around the body</p> Signup and view all the answers

    Study Notes

    Thermal Stress Lecture Objectives

    • Explain how thermal balance is maintained in the body
    • Describe four physical factors contributing to heat balance
    • Understand cardiac output, heart rate, and stroke volume response during physical activity in hot weather
    • Explain how acclimatization, training, age, gender, and body fat modify heat tolerance during physical activity

    Heat Cramps, Exhaustion, and Stroke Lecture Objectives

    • Understand symptoms, causes, and treatments for heat cramps, heat exhaustion, and heat stroke
    • Understand the purpose of the wind-chill temperature index and factors comprising it
    • Discuss immediate and long physiologic adjustments to cold stress

    Temperature

    • Temperature represents mean kinetic energy of a substance’s atoms
    • Functional definition of temperature: Potential for heat exchange between substances (e.g., blood to capillary walls) or objects (e.g., playing surface to participant's body).
    • Humans can tolerate a decline in deep body temperature of -10°C but only an increase of +5°C

    Body Temperature Measurement

    • Core temperature (Tc): 36.1 – 37.8°C (97 – 100°F)
    • Skin temperature (Tsk): 33.3°C (91.4°F)

    Thermoregulation

    • The process whereby the body temperature is maintained or controlled under a wide range of environmental conditions

    Assessing High Environmental Temperatures

    • Relative Humidity: The moisture in the air relative to how much moisture (water vapor) the air can hold at a given condition
    • Heat Stress Index: A measure used to estimate the risk of heat stress based on ambient temperature and relative humidity
    • Wet Bulb Globe Temperature (WBGT): A scale, developed by the military, used to assess thermal heat load imposed by the environment. Commonly used in industrial settings and athletic situations

    Thermal Balance

    • Core temperature represents a dynamic equilibrium between factors that add and subtract body heat
    • Core temperature rises if heat gain exceeds heat loss (e.g., during vigorous exercise in warm, humid environments)
    • Core temperature declines in cold when heat loss exceeds heat production

    Heat Exchange During Exercise

    • 60-minute exercise performed at 900 kpm/min-1 at different ambient temperatures

    Effect of Clothing (Uniforms)

    • Football equipment and clothing seal off 50% of the body from evaporative cooling benefits
    • Football gear exacerbates increases in rectal and skin temperatures with exercise

    What Happens When You Get Overheated?

    • The increase in body temperature that occurs with exercise
    • Physiological mechanisms used to dissipate heat
    • Increase in sweating rate (evaporation)
    • Vasodilation of the cutaneous (skin vessels)

    Thermoregulation

    • Hypothalamus coordinates temperature regulation; acts as a thermostat set at 37°C ± 1°C
    • Initiates responses to protect from buildup or loss of heat
    • Activation of heat-regulating mechanisms
    • Thermal receptors in skin provide input to central control center
    • Temperature of blood perfusing hypothalamus directly stimulates

    Role of Skin and Subcutaneous Tissues

    • Water vapor pressure gradient between skin and air
    • Evaporation, convection, and conduction transfer heat out of the body
    • Blood vessels in dermis; arrector muscles of hair react to heat
    • Increased blood flow to the skin dissipates heat; decreased blood flow conserves heat

    Blood Flow Redistribution

    • Thermoneutral (25.0°C) and Heat (43.3°C)

    Exercise in the Heat

    • Cardiac output, heart rate, and stroke volume increases

    OLD vs Young; Men vs women

    • Comparison of heart rate with exercise intensity

    Exercise Intensity and Body Temp

    • Core temperatures, sweat rates, and heat stress in various exercises (uncompensable/compensable/prescriptive zones)

    Example of a Heat Stress Study

    • The Impact of Heat Exposure and Repeated Exercise on Circulating Stress Hormones

    Core Body Temperature Response

    • Rectal temperature response during room temperature and heat exposure at different exercise levels and times

    Heart Rate

    • Heart rate response during room temperature and heat exposure at different exercise levels and times

    Plasma and Blood Volume

    • Plasma and blood volume response in room temperature and heat exposure conditions

    Catecholamine Response

    • Epinephrine and norepinephrine response in room temperature and heat exposure conditions

    Cortisol and HGh Response

    • Cortisol and hGH responses in room temperature and heat exposure conditions

    Factors Affecting the CV Response to Heat

    • Age and gender
    • Hydration: Dehydration increases physiological strain
    • Fitness level: Fitness improves thermoregulatory function and heat tolerance
    • Body composition
    • Acclimatization: Adaptive changes occur when exposed to stressful environments; reduces strain. (Adipose tissue interferes with heat dissipation and increases metabolic cost of activity)

    Acclimatization to Heat

    • Improved cutaneous blood flow, effective redistribution of cardiac output, lowered threshold for sweating, and increased sweat output
    • Lowered salt concentration in sweat, lower skin and core temperatures and heart rate during standard exercise, less reliance on carbohydrate catabolism during exercise

    Acclimatization Effects

    • Core temperature, heart rate, and sweat rate response over time in unacclimatized/acclimatized individuals

    Hydration Level in Various Sports

    • Sweat rate and voluntary fluid intake in various sports

    Fluid Ingestion During and after Exercise

    • The ingestion and absorption of fluids during and after exercise and associated issues

    Heat Illness

    • Probably the greatest stress on the human cardiovascular system is the combination of exercise and hyperthermia
    • This stresses can present life-threatening challenges, especially for highly motivated athletes exercising in hot environments

    Minor Exertional Heat Illness

    • Heat cramps: acute disorder characterized by brief, recurrent, and excruciating pain in voluntary muscles of legs, arms, or abdomen
    • Heat syncope: temporary circulatory failure due to pooling of blood in peripheral veins and reduced ventricular filling; leading to a decrease in cardiac output

    Major Exertional Heat Illness

    • Heat exhaustion: rapid and weak pulse, fatigue, weakness, profuse sweating, psychological disorientation, and fainting
    • Heat stroke: serious medical emergency characterized by elevated skin and core temperatures, tachycardia, vomiting, diarrhea, hallucinations, and coma

    Exertional Heat Illness

    • Symptoms of exertional heat illness (mild, moderate, and severe signs/symptoms)

    Treatment of Heat Illness

    • Treatment procedures for each type of heat illness

    Cold Exposure

    • Human exposure to extreme cold produces significant physiologic and psychological challenges
    • Further compromise of core temperature in chronic exertional fatigue, sleep loss, inadequate nourishment, reduced tissue insulation, and reduced/depressed shivering heat production

    Hypothermia

    • Decrease in body’s temperature (3 stages)
    • Stage 1: Body temp drops 1-2°C below normal (35-34°C)
      • Loss of complex motor tasks, breathing becomes rapid & shallow
      • Loss of neuromuscular function at subsequent lower temps
    • Stage 2: Body temp drops 2-4°C below normal (34-32°C)
    • Stage 3: Body temp below 32°C
      • Impaired organ function
      • Death may occur

    Physiological Changes with Reduced Core Temperature

    • Physiological changes in body temperature across stages (mild, moderate, and severe)

    Body Fat, Physical Activity, and Cold Stress

    • Differences in body fat influence cold function
    • Increased subcutaneous fat improves/increases cold insulation in swimmers and exercisers

    How Cold is "Too Cold"?

    • Increased peripheral vasoconstriction during cold exposure
    • Dangerously low skin and extremity temperatures
    • Factors that contribute to frostbite and other cold injuries: alcohol use, low fitness, and fatigue, dehydration, poor peripheral circulation

    Wind Chill Index

    • Provides a useful way to understand dangers from winter winds and freezing temperatures and provides frostbite threshold values

    Cold Stress

    • Physiological thermoregulation in the cold, monitored by cold receptors in the skin, abdominal viscera, spinal cord, change/rate of decrease in temperature, in numbers compared with heat receptors (differing actions), and signal to other parts of body

    What Happens When You Get Cold?

    • Decrease in environmental temperature
    • Decrease in skin temperature
    • Piloerection (hair stands up)
    • Peripheral vasoconstriction
    • Shivering
    • Increased metabolic rate (BMR)
    • Increased heat production

    Acute Adaptations to Cold Stress

    • Physiological responses to cold; cessation of sweating, increased shivering, peripheral vasoconstriction, thyroid hormone release, and sympathetic stimulation

    Exercise in the Cold

    • Decreased nerve conduction velocity and neuromuscular activity
    • Reduction in force production, diminished power output, decreased time to peak power, and associated injuries (exercise-induced asthma/increased ventilation/higher oxygen consumption/metabolic changes/increased reliance on CHO)

    Cold Acclimatization

    • natural/artificial environment, behavioral changes, psychological, and physiological adaptations

    Cold Stress Study

    Exercise and Cold Stress

    • Various processes and data used in an experiment/case study examining the effects of exercise and cold

    Rectal Temperature

    • Monitoring rectal temperature changes during different procedures and conditions

    Signs/Symptoms of Lowered Body Temperature

    • Constant shivering, blue lips/fingers, confused behavior, poor coordination, decreased mental capacity, and decreased physiological performance

    Risk Factors for Cold Injury

    Cold Stress and the Skin - Nonfreezing/Freezing Injuries

    • Types of cold injuries to the skin

    Mechanism of Frostbite

    • Frostbite mechanism and conditions

    Cold Weather Clothing and Thermoregulation

    • Factors affecting clothing's clo (insulation value)

    Questions?

    • Blank page for questions

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    Lecture 7 Kin. PDF - Thermal Stress (2024-11-11)

    Description

    This quiz explores the effects of physical activity and environmental factors on heat tolerance. It covers topics such as cardiac output, thermoregulation, and indicators of heat-related conditions during exercise. Test your knowledge on how the human body responds to heat stress and the physiological parameters involved.

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