Water and Temperature Regulation PDF

 Requirements depend on BW of the individual, stages of life cycle, environmental temperature, activity levels.  Normal conditions: ◦ Males: AI= 3.7 L. ◦ Females: AI= 2.7 L.  To maintain balance, output of fluids should match input.  Losses of water: ◦ Feces: small amou...

 Requirements depend on BW of the individual, stages of life cycle, environmental temperature, activity levels.  Normal conditions: ◦ Males: AI= 3.7 L. ◦ Females: AI= 2.7 L.  To maintain balance, output of fluids should match input.  Losses of water: ◦ Feces: small amounts (100 ml). ◦ Exhaled air (300 ml). ◦ Insensible perspiration on the skin (30% of losses = 750 ml). ◦ Sweat losses. ◦ Urinary output: main avenue (1650 ml).  Water intake: 20% come from solid foods and 80% from fluids: ◦ Food (vegetables, fruits, meats…) (500 ml). ◦ Metabolism of food for energy (300 ml). ◦ Fluids: 2000 ml.  Water may contain minerals ( Ca, Na, Mg, Fe, Zn, As, lead…).  Contaminants like pesticides.  FDA definition of bottled waters: ◦ Mineral: comes from a protected underground source and must contain minerals distinguishing it from other waters. ◦ Spring water: flows naturally from an underground source. ◦ Purified water: is produced by distillation or other processes.  60-65% = intracellular.  35-40% = extracellular (intercellular + intravascular).  Water held in the body in conjunction with prot, CHO and electrolytes.  Fluids shifts such as decrease in blood V and cellular dehydration contribute to the onset of fatigue (ex in heat).  Normal BW males: 60% of water.  Normal BW females: 50% of water.  Obese individuals: 40% of water.  Muscular individuals: 70% of water. (because fat tissue is low in water content, and muscle tissue is high in water content).  Normohydration = euhydration = normal body water level.  Dehydration causes hypohydration (low body water level).  Hyperhydration = retaining excess body fluids.  Normal kidney function maintains water and Na balance.  Main feed back device for the control of body water is kidney 1) The osmolality of body fluids. ◦ Also tonicity is important (= tension or pressure). ◦ These affect osmolality: a. Glucose b. Protein c. Several electrolytes, most notably sodium 2) If blood levels of solutes are high then solution is hypertonic; if low then hypotonic.  3) Feedback mechanism for control of body H2O, dehydration:  a. Osmoreceptors in hypothalamus - sensitive to changes  b. React to more concentrated body fluids by inc. release of ADH from pituitary → travels by blood to kidneys; directs them to reabsorb more H2O  E.g: In case of dehydration: Inc. concentration of blood (hypertonic) → drawing of water from body cells → secretion of ADH or vasopresssin by stimulation of osmoreceptors→ reabsorption of water by kidneys (Urinary H2O output dec. considerably).  4) During hyperhydration, a reverse process inc. H2O excretion  Essential building material for cell protoplasm.  Protection of key body tissues (spinal cord, brain).  Control of osmotic pressure.  Main constituent of blood.  Proper functioning of senses (hear, vision..).  Regulation of body temperature.  To make sure of good hydration: ◦ Sensation of thirst may be a good guide to hydration status during ex. ◦ Deeply colored urine secreted in small amounts = hypohydration. ◦ Changes in BW is also reliable to evaluate hydration status.  Decrease risk of bladder and colon cancer.  Weight control by suppressing hunger.  Water from foods is accompanied with vitamins and minerals.  Definition: substance which, in solution, conducts an electric current.  Major electrolytes: Na, K, Cl, bicarbonates, sulfate, Mg, Ca. Electrolyte AI Major functions Deficiency Excess symptoms symptoms Primary positive ion in Hyponatremia, Hypertension in EC fluid; nerve impulse muscle cramps, susceptible 1500 mg conduction; muscle nausea, vomiting, individuals (min Sodium contraction; acid-base loss of appetite, requirements balance; blood V dizziness, are 500 mg) homeostasis and seizures, shock, osmotic pressure coma Primary negative ion in Rare; may be Hypertension, in EC fluid, work with Na caused by excess conjunction with 2300 mg Chloride in nerve impulse vomiting and excess sodium 750 mg min conduction…, HCl loss of HCl, formation convulsions Primary positive ion in Hypokalemia, Hyperkalemia, intracellular fluid, same loss of appetite, Cardiac Estimates functions as Na, glc muscle cramps arrhythmias and daily adult Potassium transport into cell and weakness, possible death. requirements (storage of gly). apathy, irregular 2000 mg heart beat, cardiac arrest.  Concentration  in blood during exercise → helps maintain blood volume Exercise →  secretion of ADH and aldosterone (helps conserve body H20 and Na+)  Prolonged sweating while exercising in heat may lead to short-term deficiency; may be debilitating to athlete  Hypothalamus regulates sodium and H20 balance in body  If prolonged sweating while exercising in heat → Na loss  We mean here the internal or core temperature not the shell temperature that varies with environmental T.  Normal T = 37 °C (98.6°F) (range from 36.1-40 °C).  2 most common methods to measure T is orally and rectally (0.5-1°F higher).  Humans are heat-producing machines by normal burning (oxidation) of CHO, fat and protein.  It increases with higher BMR, infectious diseases, shivering and exercise.  Heat loss is governed by 4 physical means: ◦ Conduction: direct physical contact. ◦ Convection: transfer by movement of air or water. ◦ Radiation: from body into the surrounding air. ◦ Evaporation: by converting sweat to vapor.  Normally, body heat is transported from the core to the shell by the ways of conduction and convection (the blood is the carrier).  Exercising in sunlight increases heat to the body.  Factors that increase heat loss: ◦ Cooler environment ◦ Increased air movement ◦ Increased blood circulation to skin  Heat balance equation: H= M ± W ± C ± R – E where H = heat balance M = resting metabolic rate. W= work done. C= conduction and convection. R= radiation. E= evaporation.  Body temperature is controlled by the autonomic division of the CNS, especially the hypothalamus. Hypothalamus receives input from the skin and from the blood. If there is detection of temperature increase ➔ adjustments to lose heat. Blood channeled closer to the skin so heat can be radiated. Sweating. If there is detection of a colder temperature: Blood shunted away from the skin to the central core of body. Shivering (by increasing the metabolic rate due to muscle contraction). Certain conditions may threaten temperature control (e.g falling in cold water cause hypothermia/ slow runners in the latter part of an exercise in cold). Most prevalent threat to the athletic individual is hyperthermia.  Air temperature: +++ if higher than 27 degrees or in presence of humidity. Relative humidity: that impairs ability of sweat on the skin to vaporize and cool the body (+++ if higher than 50-60%). Air movement: still air limits heat carried away by convection. Radiation: from the sun. The total amount of heat produced in the body depends on the intensity and duration of the exercise. Specific heat is defined as the heat in calories required to raise the temperature of 1 kg of a substance by 1 degree. Specific heat in body = 0.83 (0.83 Cal will raise 1 kg of the body 1 ° C).  Exercise in a cold environment: heat lost through radiation and convection mainly, and through little evaporation of sweat. In warm conditions, sweat evaporation is the main way to control increase in temperature. Sweat rates vary considerably between individuals. Maximum evaporation rate = 1.8 l/h = 30 ml/min. Greater losses may occur when sweat drops off the skin without vaporizing. Only sweat that evaporates has a cooling effect. 1 L of sweat weighs 1 kg or 2.2 lbs. 1 L of sweat if perfectly evaporated, will dissipate app. 580 Cal.  Under most warm environmental circumstances, the evaporation mechanisms are able to keep the core temperature during exercise below 40 degrees. An excessive rise in the core temperature, or excessive fluid and electrolyte losses may lead to diminished performance or thermal injury. Hypothermia: Muscular incoordination Mental confusion Hyperthermia: Major factor limiting performance. Dangerous (heat stroke) Air temperature > 26.6 °C. Humidity levels: 90-100%, heat loss via evaporation nears zero. Caution when relative humidity > 50-60%, especially with warmer temperatures. 1. Voluntary dehydration: 1. Exercise induced sweating. 2. Thermal induced sweating (saunas). ➔ goal: qualify for lower W classes (wrestlers). 3. Diuretics. 4. Decreased intake of fluids and food. Significant impairment with body weight losses as low as 4%. 2. Involuntary dehydration: 1. May occur in cold and hot environment, but the negative side effects are more severe in the second case (heavy sweat losses). Dehydration affects performance because it: Increases physiologic strain and perceived effort to perform the same exercise task. Anaerobic muscular endurance tasks > 20-30 min impaired when subjects were hypo hydrated. Degrades aerobic exercise performance (+++ involuntary dehydration). Adverse effects on cardiovascular function Maximal aerobic power decreases by 4-8 % with 3% weight loss during exercise Dehydration level and its effect on performance are related to the heat stress, exercise task, and individual’s unique biological characteristics. Dehydration effects: Dec. plasma V + Inc. plasma osmolality and viscosity. Dec. central blood V + Dec. filling of the heart. Inc. heart rate and dec. stroke V + dec. cardiac output. Dec. skin blood flow + dec. sweat rate + rise in core temperature + degradation in mental/ cognitive performance + impairment of physical performance.  When exercising strenuously in the heat, some athletes may lose 3 -4 liters/h. Several methods to evaluate sweat loss and hydration status like BW changes (reliable and easy to do but there are sources of error). A more adequate method: A. BW before exercise:70.5 kg. B. BW after exercise : 68.9 kg C. Change in BW: 1.6 kg D. Drink V during ex: + 300 ml E. Urine loss: - 100 ml. F. Sweat loss (C+ D – E): 1800 ml G. Ex time : 60 min H. Sweat rate (F/G): 30 ml/min.  Maximal sweat rate for trained athlete: 2-3 L/h. 150 lb runner could lose 3% of weight/hour. Football players may lose 11-13 lbs over a day with multiple daily workouts.  Apocrine sweat glands located in hairy areas of body. Eccrine sweat glands over the surface of the body involved in temperature regulation. Sweat derived from ECF. Sweat: 99% water (hypotonic fluid). Major electrolytes: Na, Cl (2.6 g NaCl in sweat = 45 mEq) (58 mg= 1 mEq). Other: K, Mg, Ca, Fe, Cu, Zn. Composition changes between individuals and in same individuals when acclimatized to the heat.  During ex, [k] and [ Na] increase in blood. [Mg] decreases. [ Ca] and [Cl] unchanged. But electrolyte deficiency doesn’t occur (very rare). However, electrolyte replacement is important especially that prolonged sweating has been shown to decrease body content of Na and Cl by 5-7% and K by about 1 %.  The 3 main ingredients in sports drinks are water, CHO and electrolytes: known as CHO-electrolyte solution (CES).  Common brands for CES: accelerade, gatorade, all-sport… (CHO & electrolytes).  Sugar content varies from 5-10% depending on the brand.  Caloric value from 6-12 kcal/oz.  Major electrolytes: Na, Cl, K, P.  There is difference between CES and actual sports E or E drinks which contain more CHO and other ingredients.  Read the label to choose the best CES or GES: ◦ If dehydration or hyperthermia is the primary threat to performance, then water replacement is the primary consideration. ◦ In prolonged endurance events, CHO replacement is essential. ◦ In very prolonged exercise in heat with heavy sweat (e.g: ultramarathon) ➔ electrolyte replacement.  2.6 g NaCl in sweat (= 45 mEq)  58 mg = 1 mEq.  Benefits of proper hydration ◦ Decrease fluid loss ◦ Reduce cardiovascular strain ◦ Enhance performance ◦ Prevent some heat illnesses  Techniques ◦ Skin wetting ◦ Hyperhydration ◦ Rehydration 37 Effects are equivocal  Possible beneficial effects ◦ May decrease sweat loss ◦ Psychological relief  No effects ◦ Core temperature ◦ Cardiovascular responses ◦ May encourage faster pace, more heat production 38  Possible beneficial effects ◦ Help maintain temperature regulation and cardiovascular functions when fluids may not be ingested during exercise  No effects ◦ Little evidence of beneficial effects in comparison to euhydration  ACSM recommends hyperhydration 39  The most effective technique  May have small benefits to performance in weight- control sports, such as wrestling ◦ Local muscular endurance 40  Benefits to endurance athletes ◦ Minimize ↑ in core temperature ◦ Minimize ↓ in blood volume ◦ Maintain optimal race pace for longer time  ACSM position stand focuses on rehydration 41  Gastric emptying affected by: ◦ Volume: increase in V (up to 700 ml) increase gastric emptying but large V cause discomfort. ◦ Solute or caloric density (6-8%). ◦ Osmolality: a high osmolality inhibits gastric emptying (+++ if >10%). ◦ Drink T: cold fluids empty rapidly. ◦ Ex intensity: moderate ex facilitates emptying, but intense one (70-75% VO2 max) exert an inhibitory effect. ◦ Mode of exercise: no difference between cycling and running. ◦ Dehydration: excessive dehydration may inhibit gastric emptying (>3% of BW).  Intestinal absorption: ◦ Water is absorbed by passive diffusion, and is helped by concurrent absorption of Na and glucose. ◦ But excess CHO in intestine cause a reverse osmotic effect → GI distress, cramping, diarrhea. ◦ High-intensity exercise compromise blood flow to the intestine which may impair absorption. ◦ Rate of absorption differs between individuals ➔ endurance athletes are recommended to train their stomach to handle larger amounts of fluids during exercise.  Appropriate amount of CHO may maintain body T as effectively as water and may enhance performance during prolonged ex.  They complement each other. When both are consumed, the beneficial effects were additive.  In general, CES between 5-10% seem to empty from the stomach as effectively as water during prolonged ex.  Solutions higher than 10-12% may significantly delay gastric emptying, decrease intestinal absorption and cause GI distress. ➔ Although CHO ingestion may not enhance the performance of all events, there are no disadvantages to the consumption of beverages containing recommended amounts of CHO and electrolytes.  During ex: ◦ Body fluids become hypertonic during moderately prolonged ex ➔ electrolyte replacement not necessary. ◦ Even during strenuous prolonged ex with high level of sweat losses, water alone is the recommended fluid replacement, although added CHO may provide some E needed. ◦ Electrolyte replacement, +++ Na, may be necessary for some athletes in very prolonged bouts of exercise ( marathons, ultramarathons, ironman- type triathlons, all-day tournaments, tennis tournament…).  Daily replacement: ◦ Electrolyte deficiency is very rare. ◦ Water alone with balanced diet maintain proper body electrolyte levels. ◦ If not, adding salt to meals and drinks may help.  Hyponatremia is a subnormal level of Na in the blood: ◦ At rest, by high consuming of water (water intoxication). ◦ After prolonged ex (exercise associated hyponatremia EAH).  EAH defined as serum concentration of Na less than 135 mmol/l (bloating, puffiness of hands and feet, nausea, vomiting, headache).  [Na] < 120 mmol/l → epileptic-like seizures, coma, respiratory arrest, permanent brain damage, death.  Ultra endurance athletes should consume adequate salt in diet 1 week before competition.  Excessive drinking of fluids before, during and after the race  Considerable weight gain over the course of the event  Slower runners, endurance athletes > 4 hours  Females  Low body weight  Individuals with high sweat sodium losses  Heat-unacclimatized individuals  Individuals with inadequate sodium intake  Individuals who use NSAIDS 47  Do not consume fluids in excess before, during, or after exercise  Consume extra salt in days before prolonged exercise  Body weight should not increase during exercise  Consume sports drinks with increased sodium content ◦ Gatorade Endurance Formula (35 mEq Na) ◦ Typical sports drink = 20 mEq Na  Treatment ◦ Prompt medical attention is essential 48  In general, use of salt tablets to replace salt electrolytes, +++ Na, is not necessary (diet is enough).  For unacclimatized athlete or for “salty sweaters”, a slight increase in Na intake may be reasonable.  K supplements are not recommended because deficiency is very rare, and excess may be lethal.  Athletes should consume 10-25 g salt daily during 1-2 weeks acclimatization to exercising in the heat.  Salt tablets: ◦ Only if substantial amounts of weight loss via sweat during workout  Only if athlete needs to drink more than 4 quarts (1 quart = 946 ml) of fluid/day.  2 salt tablets with each additional quart of fluid beyond 4 quarts.  Salt tablets should be discontinued after athlete is acclimatized (usually 6-9 days) A. Symptoms: (1) Weakness (2) Chills (3) Nausea (4) Headache (5) Faintness (6) Disorientation (7) Muscle cramping (8) Cessation of sweating B. The  fitness level,  tolerance to heat stress C. Gender Female heat tolerance similar to males D. Age: Young children may produce more metabolic heat during exercise in comparison to their body size. (1) They do not have as great a sweating capacity (2) Reduced capacity to convey heat from the core to skin. 1. Fat deters heat losses 2. Obese individuals generate more heat during exercise because of low level of fitness 3. Previous history of heat injury → less tolerant to exercise in heat * Degree of acclimatization - most important factor 1. Check temperature and humidity conditions before exercising/ slow pace 2. Exercise in the cool of the morning or evening 3. Exercise in shade; or wear sunscreen 4. Wear minimal clothing (loose, light colored, and porous) 5. Run with wind first, against wind later. 6. Drink cold fluids periodically 7. Avoid excessive intake of protein 8. Avoid beverages with caffeine several hours before exercising (check your response) 1. Avoid ephedrine. 2. Replenish your water daily; weigh yourself 3. Hyperhydrate before prolonged exercise 4. Replenish lost electrolytes (sodium, potassium) 5. Avoid alcohol 6. Use caution if overweight, sedentary, aged 7. Know signs and symptoms of heat illnesses 8. Do not exercise if ill or with fever 9. Check your medications; some may impair skin blood flow 10. Acclimatize yourself to exercise in the heat Active acclimatization: a. When hot weather begins, moderate activity b. After initial reduction, gradually increase activity (duration or intensity) c. Process takes ~ 1-2 weeks (longer in children) d. Endurance will be less than under cooler conditions Cool climate acclimatization tips: a. Exercise indoors at a warmer temperature b. Wear extra layers of clothing c. Body adjustments during acclimatization to heat ~ 6-8 days; full acclimatization: > 14 days 1. Plasma volume  to  total blood volume (inc. Na and prot). 2.  Blood volume allows heart to pump more blood/beat 3. When volume  more blood flow to the muscles and skin. 4. Sweat glands hypertrophy; secrete ~ 30 % more sweat, →  evaporative heat loss (sweating at a lower core temperature) 5. Salt in sweat  60%; electrolytes are conserved 6. Dec muscle gly usage 7. Dec. the rate of core temperature increase. 8. Dec psychological feeling of stress.