Study Guide EXAM 4

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Chapter 14 – Exercise in hot and cold enviornments 1. Humans are homeothermic (what does it mean?) a. Internal body temperature is physiologically regulated to keep it nearly constant even when environmental temperature changes. 2. Metabolic heat production (cellular work vs. metabolic heat.) a. 25% of the body’s ATP used for physiological functions , remaining 75% is converted to heat. 3. 4 means of heat loss. a. Conduction i. Heat loss when the skin contacts a cold object or gain when a hot object is pressed against the skin. b. Convection i. When air or water moves across the skin, exchanging heat with the environment. 1. Critical for heat dissipation if the air temperature is lower than the skin temperature. 2. Convection and radiation at rest are the two primary ways to maintain temperature regulation. c. Radiation i. The skin continuously emits heat in all directions to surrounding objects like clothing, furniture, and walls. d. Evaporation i. When sweat evaporates from the surface of your skin, it removes excess heat and cools you. 1. During exercise , the primary method of heat dissipation is evaporation. 2. Evaporation accounts for approximately 80% of total heat loss during physical activity. 4. What regulates body temperature (central and peripheral nervous system)? a. The preoptic-anterior hypothalamus (PAOH) acts as the body’s thermostat, maintain a set point. i. Peripheral Thermoreceptors: in the skin monitor external temperature changes.

ii. Central Thermoreceptors: in the hypothalamus and other areas monitor blood temperature changes. 5. Physiological responses to exercise in the heat. a. Cardiovascular system (stroke volume, heart rate, cardiac output, dehydration). i. Exercise increases demands on the cardiovascular system. During exercise the blood must reach both working muscles and the skin for heat dissipation. ii. Stroke Volume: decrease in SV , decreased preload due to lower plasma volume (sweating). iii. Heart Rate: increase in HR to maintain CO due to decrease SV. iv. Cardiac Output: may remain reasonably constant or decrease slightly at higher intensities. v. Dehydration: exacerbates the cardiovascular strain 1. prolonged heavy sweating can lead to dehydration and excessive electrolyte loss. b. Critical temperature theory. i. Proposes that the brain signals to stop exercise when a critical brain temperature is reached (~40-41°C) c. Changes in sweat composition with training and sweat loss during exercise. i. Sweat composition reflects blood plasma electrolytes. 1. Training and heat acclimation (adaptations) increase Na + and Cl - reabsorption and make the sweat is more dilute (reduce loss of Na + and Cl - ) 2. K + , Ca2 + , and Mg 2+ are not reabsorbed , found in similar concentrations in sweat and plasma (no effect) ii. Heavy exercise in hot conditions can lead to loss of 1L – 1.6L of sweat per hour  2.5% to 3.2% of body weight can be lost in sweat. 1. Sweat triggers the release of aldosterone and ADH which enhance sodium and water retention. 6. Precooling and sport performance. a. Laboratory studies show precooling allows longer exercise at a given intensity in hot conditions. i. Improvements seen in endurance events w/ detrimental impact on short sprints. 7. Health risks.

a. Six risk factors that must be considered when exercising in the heat. i. Metabolic Heat Production, Air Temperature, Humidity, Air Velocity, Radiant Heat Sources, and Clothing. 1. Heat index alone does not reflect physiological stress. b. Measuring external heat stress. i. Wet Bulb Globe Temperature (WBGT) c. Heat cramps, heat exhaustion, heatstroke. i. Heat Cramps: severe cramping of large skeletal muscles, caused by sodium loss due to dehydration from excessive sweating. Can be prevented by proper hydration practice and electrolyte replacement. ii. Heat Exhaustion: characterized by extreme fatigue, dizziness, nausea, and fainting  result of inadequate blood volume because of dehydration. iii. Heat Stroke: life-threating disorder w/ core temperature exceeding 40C (104F), result of thermoregulatory mechanism failure. d. How can you prevent hyperthermia? i. Schedule events in the early morning or late evening to avoid midday heat stress. ii. Stay adequately hydrated with drink breaks every 15 to 30 minutes to match fluid intake to sweat loss. iii. Choose minimal, light-colored, and loosely woven clothing to reduce heat stress. 8. Acclimation vs. acclimatization. a. Acclimation: physiological changes occur over short periods of time b. Acclimatization: gradual set of adaptations occurs in people who adapt to hot conditions by living in hot environments for months to years. c. Effects i. With moderate-intensity exercise in the heat, people generally acclimate in 9 to 14 exposure days. ii. Improved cardiovascular function, enhcnaced heat dissipation, and reduced physiological strain. 1. Changes in blood volume, cardiovascular function, and sweating. a. Plasma volume increases early in the process , contributing to an increase in stroke volume; allows CO to be maintained to support active muscles and skin (sweat). b. Lower core body temperature during exercise.

c. Changes in sweating rate, sweat distribution, and sweat content. d. Sex differences i. Women’s responses almost identical to men’s when exercise intensity is adjusted relative to VO2max. 1. Women generally have lower sweat rates but more active sweat glands than men. 9. Exercise in the cold. a. Review Figure 14.13: Thermoregulatory mechanisms by which humans strive to maintain a relatively constant body core temperature. i. In thermoneutral zone, minor adjustments to skin blood flow regulate heat loss or gain. ii. Maximal vasoconstriction may not suffice, leading to metabolic regulation Nonshivering thermogenesis and shivering increase metabolic heat production. b. Characteristics of the distinct patterns of adaptation to repeated cold exposure. i. Cold Habituation: skin vasoconstrictor and shivering responses are blunted.

1. body temperature may decline more in the acclimatized than unacclimatized state. ii. Metabolic Acclimation: enhanced nonshivering and shivering thermogenesis develop. iii. Insulative Acclimation: enhanced skin vasoconstriction occurs, which increases peripheral insulation and minimizes heat loss. c. Heat loss and body composition. i. Body Size and Composition: Insulation against cold is crucial for protection against hypothermia. Inactive peripheral muscles and subcutaneous fat act as effective insulators. 1. Larger individuals, with a smaller body surface area to mass ratio, are less susceptible to hypothermia due to reduced heat loss. 2. Children's high surface area to mass ratio increases heat loss. ii. Women advantage in cold exposure due to more subcutaneous fat, but disadvantage in extreme cold because of less muscle mass to utilize for shivering. d. Thermal conductivity of water. i. Prolonged exposure or very cold water can lead to extreme hypothermia and death. 1. At 4 °C (39.2 °F) water temperature, rectal temperature decreases at a rate of 3.2 °C (5.8 °F) per hour. e. Physiological responses i. Muscle Function: cooling reduces muscle force and contractility. 1. Cold affects small peripheral muscles, which leads to a loss of manual dexterity. ii. Metabolic Responses: 1. Prolonged exercise increased mobilization and oxidation of FFAs because of release of catecholamines. a. Vasoconstriction impairs circulation to peripheral fat stores, so this process is weakened. 2. During prolonged cold exposure, individuals shift from relying on carbohydrates to favoring lipid oxidation, preserving limited muscle glycogen stores. iii. Fuel For Shivering: 1. During the beginning of cold exposure, individuals mainly use carbohydrates.

2. Shift to lipid oxidation, to preserve limited muscle glycogen stores. iv. During exercise in the cold the primary metabolic substrate is glucose/glycogen despite increased circulating catecholamines f. Health risks i. Hypothermia: hypothalamus begins to lose its ability to regulate body temperature when core temperature drops below about 34.5 °C (94.1 °F). ii. Cardiorespiratory Effects of Cold: affects the heart’s sinoatrial node, decreasing the heart rate, which in turn reduces cardiac output. iii. Frostbite: body’s attempt to prevent heat loss by skin vasoconstriction, can cause cutaneous tissue to die. iv. Exercise-Induced Asthma: mainly due to drying of airways from high respiration rate during exercise and dry air in cold temperatures. Chapter 15 - Altitude, Hyperbaric Environments, and Microgravity. 1. Low Oxygen Conditions: a. Hypobaria: Low Pressure b. Hypoxia: Low Oxygen c. Hypoxemia: Low Oxygen in Blood 2. How is well-being and performance affected at the different altitudes. a. Sea Level (<500 m): No altitude effects on well-being or exercise performance. b. Low Altitude (500-2,000 m): Well-being unaffected; performance may diminish, especially above 1,500 m. Acclimation can mitigate performance decrements. c. Moderate Altitude (2,000-3,000 m): Potential effects on well-being, decreased maximal aerobic capacity, and performance. Acclimation may or may not restore optimal performance. d. High Altitude (3,000-5,500 m): Adverse health effects (e.g., acute mountain sickness) in many individuals, and notable performance decrements persist even after full acclimation. e. Extreme Altitude (>5,500 m): Severe hypoxic effects; highest permanent human settlements at 5,200 to 5,800 m. 3. Characteristics of air temperature and humidity at altitude. a. Air Temperature: As altitude ascends, the air temperature declines. b. Humidity: Decreases with altitude  air tends to become drier. 4. Physiological responses to altitude exposure. a. Pulmonary Ventilation: Immediate increase in V E , result of low PO2 levels with increase in elevation. b. pH: Increased ventilation decrease PCO2, which increases pH (respiratory alkalosis) c. Kidneys: Increased release of erythropoietin and excrete more bicarbonate ions. d. Pulmonary Diffusion: Diffusion gradient that allows oxygen exchange between the blood and active tissue is substantially reduced.

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