•Water, Electrolytes, Temperature Regulation Chapter 9 PDF

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•Water, Electrolytes, Temperature Regulation

Introduction •Water •Electrolytes •Temperature regulation •Exercise performance in the heat •Fluid, carbohydrate and electrolyte replacement •Ergogenics •Heat illnesses •Body water •For adult males, –60% of body weight is water. üGreater amount of muscle, compared with femalesà higher water content •For adult females –50% of body weight is water. üGreater amount of body fat, compared with males à lower water content •Percentages of body water may vary –70 percent in muscular individuals –40 percent in obese individuals •Where is water stored in the body? •Body Water Regulation: Terminology •Normohydration (euhydration) –Normal body water stores •Dehydration –Process of losing body fluids •Hypohydration –Low levels of body water ü Hypohydration and dehydration are used

interchangeably. •Hyperhydration –Process of increasing body fluids –Above normal levels of body water •Body Water Regulation •Concentration of body water depends on –osmolality (the absolute concentration of a solution expressed as the total number of solutes) or –tonicity (the relative concentration of solute of body fluids) •Isotonic •Hypotonic •Hypertonic •Substances affecting osmolality are -glucose, protein, and electrolytes (e.g., sodium, potassium) •Body water flows from a hypotonic area to a hypertonic area (e.g., osmosis). •Hypohydration •Hyperhydration (water intoxication) •Risk of hyperhydration Excessive amount of water can eliminate necessary electrolytes due to increased water excretion via Na2+ release. This will be potentially fatal disturbance to the brain. •How do I know if I am adequately hydrated? •Thirst (but when you become dehydrated, you become insensitive to thirst) •Urine color –Deep yellow may indicate hypohydration •Cf. Riboflavin vitamin may cause deep yellow urine color •Body weight changes

–Rapid body weight changes are due to body water loss or gain •Why Do We Need Water? Major functions of water in the body •Essential building material for cell cytoplasm –ATP hydrolysis, lipolysis, and proteolysis •Protection of organs such as brain and spinal cord •Maintenance of electrolyte balance and key cellular functions •Main constituent of blood (reduce viscosity) •Proper functioning of senses (eyes, ears) •Regulation of body temperature •Drinking water or fluids and health benefits •Possible health benefits –Decreased risk of bladder cancer –Decreased risk of colon cancer –Suppression of appetite in weight control •Electrolytes •Electrolytes are substances becoming ion (cation or anion) in solution that conducts an electric current. –Electrolytes in the human body are üSodium (Na2+), Potassium (K+), Calcium (Ca2+), Magnesium (Mg2+), Chloride (Cl-), Bicarbonate (HCO3-), and Sulfate (SO2-). •Function of electrolytes are –Electrical currents in nerves and muscles (membrane potential) –Gas exchange (CO2 removal in the blood: HCO3- and Cl-) –Activate enzymes to control metabolism •Sodium (Na2+) - Major functions •Principal electrolyte in extracellular fluids –Nerve impulse conduction –Initiate neural process (depolarization) of muscle contraction •Maintains normal body-fluid balance and osmotic pressure

•Essential for control of blood volume and pressure •Sodium - Deficiency and excess •Sodium concentration –Low blood sodium levels ↑ aldosterone from the adrenal gland (cortex), stimulating kidneys to reabsorb sodium –High sodium concentration ↓ aldosterone, stimulating kidneys to excrete sodium via urine •ADH from the posterior pituitary gland helps Na2+ equilibrium by reabsorption of Na2+ and water at the kidney. •Short-term Na2+ deficiencies may impair exercise performance •Sodium and Exercise •Maintenance of blood volume –Exercise increases ADH and aldosterone for water retention by reabsorbing Na2+(prevention of Na2+ loss). •Potassium (K+: kalium) •Cation •Food sources –Found in most foods –Especially abundant in fruits, vegetables, meat, and milk • •Potassium (K+) •Major Function -Important intracellular electrolyte -Works with sodium and chloride –Electrical impulses (nerve, muscle including the heart) -Glucose transport into cells (insulin secretion from a beta cell of pancreas by initiating K+accumulation) -Glycogen metabolism (glycogen synthesis) • • •Potassium - Deficiency and Excess

•Deficiency and excess are rare •Similar to sodium, potassium balance is regulated by aldosterone, but in a reverse way. •Excessive serum K+ stimulates aldosterone release. –The increased aldosterone promotes the excretion of K+ into urine. •Low serum K+ decreases aldosterone release, resulting in an increase in K+ absorption by the kidney. •Potassium - Deficiency and excess •Hypokalemia (diarrhea) –Hyperthyroidism is associated with it. –Muscular weakness; irregular heartbeat; death • •Hyperkalemia (excess supplement use) –Interference with skeletal muscle function –Suppression of electrical activity of the heart (early depolarization but inhibition of action potential) –Cardiac arrhythmias or cardiac arrest (a mortality rate of about 67%) •Sodium and potassium balance 1.Decrease in plasma volume or a low sodium concentration stimulates kidney to release renin, which produces angiotensin I from angiotensinogen released from the liver. 2.Angiotensin I will be converted to angiotensin II. 3.Then, angiotensin stimulates the adrenal glands to secrete aldosterone. 4.The aldosterone promotes sodium reabsorption in the kidney as well as potassium excretion, leading to an increase in water retention. 5.With the final low potassium, aldosterone synthesis and release is decreased, terminating potassium excretion once the ideal plasma volume is reached. •Regulation of Body Temperature •Core temperature –Internal temperature •Oral

•Rectal •Esophageal •Gastrointestinal tract (capsule) –Normal range: 97-99˚F (36.1-37.2˚C) –Typical oral temperature: 98.6 ˚F = 37˚C •Major factors that influence body temperature H = M ± W ± C ± C ± R – E H = Heat balance M = Resting metabolic rate W = Work (exercise) C = Conduction C = Convection R = Radiation E = Evaporation

•Major factors that influence body temperature •Conduction –Heat is transferred from the body by direct physical contact •Convection –Heat is transferred by wind or water over the body •Radiation –Heat energy radiates from the body (high temp.) into the surrounding air (low temp.) •Evaporation –Heat is lost from the body when it is used to convert sweat to a vapor. –The lungs also help dissipate heat through evaporation. •Sources of heat gain and heat loss to the body during exercise •Body temperature regulation - Hypothalamus control

Functions as a thermostat •Input –Receptors in the skin –Blood temperature •Output –Circulatory system compensation: regulation of blood flow to the skin üSmooth muscle relaxation (vasodilation) in skin vessels increase in blood flow to the skin for heat release.

leads to an

–Sweating •What environmental conditions may predispose an athletic individual to hyperthermia? •Air temperature (hot weather): if above 80˚F (27˚C) –Radiation from body heat is limited. –Addition heat from environment (e.g., road, sun) is gained. •Air movement –Still air limits convection. •Relative humidity: if exceeds 50-60%, –Evaporation is limited. •How does exercise affect body temperature? •Normal mechanical efficiency of metabolism in human -20-25% for energy production -75-80% for heat production •If a person (70 kg or 154 lbs) jogs for 1-hour at 6-7 mph speed, about 900 Cal will be expended. - In this case, 720 Cal (80% of total Cal) would be released as heat. •Specific heat = Calorie required to raise 1˚ Celsius (C) of 1 kg body mass at rest –0.83 Cal is specific heat per kg body weight in the human. –Therefore, to increase 1˚C of body temp of 70 kg of body mass, 58 Cal (0.83 Cal/kg x 70kg) is needed. –If 720 Cal is produced as heat, body temp will increase up to 12.4 ˚C (e.g., 720 Cal x 1˚C/58 Cal) à 37˚C + 12.4˚C (heat gained) = 49.4 ˚C

–Body heart is supposed to be 49.4 ˚C, but due to the body’s cooling system the average core temp. during exercise reach only 39-40˚C, instead of 49.4 ˚C! •Body temperature at rest Increase in core temperature at rest with no heat loss •Resting for 60 minutes with 80 Cal. expenditure –80% of the Calories are released as heat or 64 Cal. –70 kg (154 pounds) runner •Storage of 58 Cal would increase body temperature by 1˚C. –Specific heat = 0.83 Calorie per kg body mass –70 kg x 0.83 Cal/kg =

58 Calories

–Body temperature would increase by 1.1 ˚C (2 ˚F) if body heat not dissipated. •64 Calories x 1 C˚/58 Calories = 1.1 ˚C •If no body heat is lost, the body temperature would become 38.1 ˚C (100.6 ˚F) instead of 37 ˚C. – • •How our body dissipates heat during exercise? Exercise in a cool or cold environment can enhance body heat loss by •Radiation and convection •Respiratory heat loss via evaporation •Skin sweat evaporation –Maximal evaporation rate is about 30 ml/minute (1.8 liter/h). –Evaporation of 1 liter of sweat can dissipate 580 Calories. •Thus, if 8˚C (464 Cal = 58 Cal/kg x 70 kg) of body heat is generated during exercise, 0.8 L of sweat is needed to cool down the body temperature. • – –Sweat rates vary among individuals. •How does environmental heat affect physical performance? •Distance running performance

–Significant inverse linear relationshipbetween heat and performance in 10-kilometer run •Marathon running performance –Running times ↑ about 1 minute for every 1˚C (1.8 ˚F) ↑ in environmental temp. •Especially, if temperature is beyond 8-15 ˚C (46-59˚ F) •Environmental heat and exercise performance -Possible mechanisms of fatigue •Central neural fatigue caused by ↑ brain temperature •Cardiovascular strain caused by changes in blood circulation (e.g., more blood pools in the skin) •Muscle metabolism changes caused by increased muscle temperature: more glycogen use •Cardiovascular drift (i.e., higher HR but no increase in CO) caused by excessive sweat losses (dehydration) •Muscle metabolism •Shift of energy metabolism occurs toward increased carbohydrate use and decreased fat use. •Muscle glycogen use is accelerated. –Possibly more rapid depletion •Rate of lactic acid production via glycogenolysis increases despite the the same exercise intensity. •Increased temperature may lead to dysfunction of muscle contraction and interferes in enzyme activities. •Dehydration and Physical Performance •Involuntary Dehydration Occurs during prolonged aerobic endurance events •In cold environments –Dehydration of 3% (body weight loss) has marginal influence on aerobic endurance performance. •Convection and radiation helps maintain optimal thermoregulation in this condition.

•In heat-stress environments –Dehydration of 2% (body weight loss) has adverse effects on aerobic endurance performance. •Cardiac stress •Involuntary Dehydration •Effects on mental/cognitive performance –May impair vigilance in dynamic sports environments, such as basketball & soccer –Progressive deterioration in basketball skills with increasing levels of dehydration from 2-4 % •How fast may an individual dehydrate while exercising? •Most athletes lose about 2-3 liters per hour when exercising in the heat •Some athletes may lose up to 10 liters (10 kg or 22 pounds) in multiple daily workouts •Males produce sweat almost twice as much as females –Females efficiently evaporate sweat on their skin without excessive perspiration (e.g., sex hormones, body comp.) •Sweat losses are highly individualistic •Factors that influence sweat rate •Environment –Air temperature –Relative humidity –Radiant heat (solar and ground) –Wind –Clothing •Factors that influence sweat rate (cont.) •Individual characteristics –Body weight –Genetic predisposition –Metabolic efficiency –Heat acclimation state

•Training status -Training effect on sweat rate -Increase in plasma volume in trained athlete •Metabolism: mitochondria (anti-dehydration)? –

H2O production through (ETC): anaerobic vs. aerobic

•Composition of Sweat Two sweat glands: Eccrine vs. Apocrine –Eccrine glands: distributed all over the body, and a primary form of cooling (thermoregulation) –Apocrine glands: limited to axilla (armpit) and perianal area for emotional stress release, not for major thermoregulation Sweat from the eccrine sweat glands: derived from blood plasma and intercellular fluid •Mostly water (99%): hypotonic to body fluids •Major electrolytes –Sodium, and chloride –[Sodium chloride] in sweat: avg. about 55 mEq(milliequivalent) = 55 mmol (3.2 g)/liter •Composition of Sweat (cont.) •Other minerals –Potassium, magnesium, calcium, iron, copper, zinc •Small quantities of nitrogen, amino acids, some water-soluble vitamins •Sweat composition may vary after acclimation •Is excessive sweating likely to create an electrolyte deficiency? •In general –Blood electrolyte concentration normally rather increases due to loss of blood volume –Prolonged sweating decreases the body content of Na2+, and Cl- (5-7%) and K+ (1%) –Acute or prolonged bouts of exercise does not cause an electrolyte deficiency •During recovery

–Replace electrolyte loss on a daily basis, or a deficiency will occur over time •Which is more important to replace during exercise in the heat: water, carbohydrate, or electrolytes? Depending upon conditions: •Water –Prevent or delay dehydration or hyperthermia •Carbohydrate –Provide energy in prolonged endurance events •Electrolytes –Prevent heat injury in very prolonged exercise in the heat • •Sports Drinks •Contents –Water –Carbohydrate –Electrolytes –Amino acids –Vitamins, minerals, caffeine, herbals •Most sports drinks are hypotonic compared to sweat –Excessive intake of sports drinks may dilute serum sodium concentrations, predisposing to hyponatremia •Guidelines For Maintaining Water Balance During Exercise •Benefits of proper hydration –Decrease fluid loss –Reduce cardiovascular strain –Enhance performance –Prevent some heat illnesses •Techniques –Skin wetting –Hyperhydration

–Rehydration • •Skin wetting Effects are equivocal •Possible beneficial effects –May decrease sweat loss –Psychological relief •No effects on –Core temperature –Cardiovascular responses •Hyperhydration •Consume 16 oz. cold water 15-30 min prior to exercise •Possible benefits –May help maintain temperature regulation and cardiovascular functions •Real effects –Little evidence of beneficial effects in comparison to euhydration •Rehydration •The most effective technique •Ingested fluids may appear in plasma and sweat within 10-20 minutes •So, drink before dehydration occurs. •Benefits to endurance athletes –Minimize ↑ in core temperature –Minimize ↓ in blood volume –Maintain optimal race pace for longer time •Factors Influencing Gastric Emptying And Intestinal Absorption for proper rehydration •Factors Influencing Gastric Emptying •Volume of fluid –Larger volumes (up to 700 ml) empty more rapidly •Caloric density

–A 6% to 8% solution appears optimal •Osmolality –Lower osmolality may empty faster •Drink temperature –Beverages in an ambient temperature of between 15-22 ˚C empty rapidly • •Factors Influencing Gastric Emptying(cont.) •Exercise intensity –Moderate-intensity facilitates emptying, whereas high intensity (> 75%) decrease emptying •Mode (types) of exercise –Little difference between running and cycling •Dehydration and body temperature –Excessive dehydration (> 3% of BW) may decrease emptying •Gender (GE is slower in women than in men.) – •Factors Influencing Intestinal Absorption •Water is absorbed rapidly by passive diffusion •Glucose-sodium co-transport –Glucose and sodium helps pull water in •Can be a problem of reverse transport of fluids (if concentration is too high) –Abdominal cramping and diarrhea •Multiple carbohydrate receptors –Use variety of monosaccharides and disaccharides •Individual differences •ACSM Fluid Replacement Guidelines Relative to Fluid Replacement during Exercise or Competition •Cold water is effective in endurance events less than 50-60 minutes. • •Sports drinks with 6-8% carbohydrates and normal electrolyte content

may also be consumed, but provide no advantages over water alone during short (less than 50-60 minutes) •ACSM Fluid Replacement Guidelines Relative to Fluid Replacement after Exercise or Competition •Goal is to fully replace any fluid and electrolyte deficit –If time is short to next exercise session, aggressive rehydration is important. •Drink 1.5 liter of fluid for every kilogram of body weight loss •Consume adequate electrolytes as well •Pretzels/other salty snacks may provide sodium and carbohydrate •If recovery time permits (24 hours), normal meal and water intake will restore euhydration and provide adequate sodium intake. • •Practice Fluid Intake during Training •Use a trial and error approach to see what works with you –Timing and amounts before exercise –Amounts consumed during exercise –Concentration of carbohydrates –Concentration of sodium –Carrying your own fluids –Experiment with brand to be used in race • •Heat syncope (fainting) •Caused by excessive vasodilation and decreased relative blood volume –Venous return ↓ and cardiac output then ↓ –Blood flow to brain is decreased •Prevention –Cool down after exercise; maintain venous return from legs •Recovery is usually rapid. • •Heat Cramps (muscle spasms)

•Theories: –Cause still remains a mystery –Fatigue and abnormal spinal control of motor neurons –Salt losses •Oral or intravenous saline can stop cramping •Prevention –Consume salt solutions at first sign of muscle twitches –EnduroLyte; GatorLYTES •Heat exhaustion •Causes –Dehydration –Inadequate salt replacement •Symptoms –Fatigue and weakness –Rapid pulse –Headache, nausea, vomiting, chills –Rectal temperature < 104⁰ F •Generally resolves with rest and fluids •Heat stroke •Cause by interaction of various factors –Hot environment –Strenuous exercise –Clothing that limits evaporation of sweat –Inadequate heat acclimatization –Too much body fat –Lack of fitness •Heat stroke •Most dangerous of heat illnesses •Symptoms –Confusion

–Disorientation –Aggressiveness –Convulsions –Rectal temperature > 104⁰ F •May be fatal •Acclimation to exercise in the heat •Cut back on the intensity and/or duration of your normal exercise routine when ambient temperatures increase •Gradually increase the intensity and duration of exercise •Full acclimatization takes about 10-14 days, but longer in children • •Heat acclimatization - Favorable adaptations ↑ total body water and blood volume ↑ sodium and protein ↑ cardiac output to muscles and skin ↑ size of sweat glands and ↑ sweat rate ↑ sweating at a lower core temperature ↓ muscle glycogen usage ↓ loss of body salt and sodium ↓ in rate of core temperature increase ↓ psychological feeling of stress •...