Water and Fluid Balance Notes
Water and Fluid Balance Notes EXSC 408
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This 10 page Class Notes was uploaded by Ticynn London on Friday April 8, 2016. The Class Notes belongs to EXSC 408 at Old Dominion University taught by Kim Baskette in Spring 2016. Since its upload, it has received 10 views. For similar materials see Nutrition in Physical Education at Old Dominion University.
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Date Created: 04/08/16
Water and Fluid Balance Comprises approximately 60% of body weight Range_ 40-80% Functions - Aqueous medium for chemical reactions/cell process - Transport of substances through the body - Thermoregulation Fluid balance - Water volume - Solute concentration Euhydration= normal fluid balance Osmosis - Movement of water through a semipermeable membrane to areas of high solute concentration Tonicity - Hypotonic- water moves in - Isotonic - Hypertonic- more soluble outside, water moves out; cells shrivel and die Tonicity - Primarily affected by electrolyte concentration Water concentration in body - Average male - 60% (approx. 42L for 70kg) - Average female – 50-55% (30L) Water distribution in body - Blood plasma - Muscles & other organ tissues - Bone - Adipose tissue Distribution of body water Intracellular fluid compartment - Approx. 2/3 of body water Extracellular fluid compartment - Approx. 1/3 of body water (14L or ~3.5 gallons) - Plasma - 20% of total ECF volume (3L or 3Qrts) - Transport; thermoregulation Interstitial fluid – 80% of total ECF (11L or 3gallons) - Protection Lymphatic system Tonicity Hypertonicity - Heavy sweating - Large loss of plasma volume + - Increased concentration of plasma Na - Water movement Hypotonicity - Consumption of large amounts of water very quickly - Nerve cells can cease to function properly - Ex. 3,000ml or ~13C in 4hrs - Dilutes ECF resulting in decreased plasma Na + Water movement Water loss Insensible – H20 loss through channels not normally noticed Sensible Primary channels – urine, sweat, feces Influences on water loss - Fluid & salt intake - Renal function- major role in fluid balance control Action of various hormones Consumption of diuretic compounds Fluid Balance Diuretics - Alcohol – inhibits production of ADH - Prescription medications- may block reabsorption of fluid &/or electrolytes - Caffeine & theophylline – increases urine output - Herbs Sweating- thermoregulatory mechanism Water intake Average daily intake - ~ 2,350ml from beverages & foods Food – 20-25% Tap and/or bottled water – 35-40% Other sources – 35-45% Aerobic metabolism – 350ml (12.5oz) of daily water Regulated by water volume & osmolality of ECF Hypernatremia & endurance athletes Clinical hypernatremia – plasma level <135mmol/L Exercise-induced hypernatremia – rapid drop less than 130 Involves endurance events lasting >7hrs with significant sweat loss Ultraendurance running events – 10% Ironman Triathletes – 29% Swelling of nerve cells can cause dizziness, confusion, seizure, coma, & death 0.5-0.7g/l fluid Strategies for prevention Replacement of Na & prevention of fluid overload Events lasting >2-3hrs should include Na replacement Sodium intake Daily intake Consumed primarily as NaCl: 1/4tsp of table salt (1000mg of NaCl has 40% Na) = 1.5g NaCl Processed food – 77% Table salt – 11% Naturally in foods – 12% Average daily Na intake Males – 4200mg Women – 3300mg Exercise and fluid balance Under normal conditions, fluid balance easily regulated Exercise: increase body temp and fluid loss via sweating Decrease in plasma volume Leakage of fluid from plasma into the interstitial spaces Dependent on intensity of exercise Intense exercise – small losses (5%) w/o sweating Prolonged exercise – large losses (10-20) w/ sweating Exercise and fluid balance Factors affecting increase in sweating Exercise intensity Environmental conditions Clothing Training status- higher sweat rates; more effective thermoregulatory Variations in sweat loss Non-exercise, normal temperature environment - 100ml Exercising in elevated temperatures – 300-1200ml/h Exercising in elevated temps with protective clothing – 1-2l/h Athletes competing in team sports & prolonged endurance events in hot environments – 2.5l/h Athletes competing in aquatic events Have been shown to have elevated sweat rates Cold climates – water loss from ventilation Hypohydration Hypovolemia: Loss of blood volume: increase osmolality of plasma Increase in body core temperature: every 1% loss of body weight as water, about 0.1-23 c increase core temp Impairment in ability to dissipate heat resulting in higher body temperatures Decreased thermoregulatory control in brain May result in hyperthermia leading to heat stroke, coma & possibly death Electrolyte loss during exercise + - Greatest loss - Na and Cl Exercising <2hrs: electrolyte loss not likely; fluid replacement should be focused on water intake Exercising >2hrs: electrolyte replacement with sodium Replenishment of water & electrolytes Determining hydration status Amount of total body water Plasma osmolality Provides accurate assessment at single point in time Analysis of urine output Higher specific gravity, osmolality, & darker color seen in hypohydration Urine testing strips available Changes in body weight Weight loss from single exercise session likely due to fluid loss Can be used as a benchmark for subsequent rehydration Ex. Athlete engages in intense exercise lasting one hour & loses 2kg 1L water weighs 1kg which translates to loss of 2L of water If only 1kg gained back the following day, signifies inadequate fluid replenishment Hydration assessment tool Pre-exercise hydration Pre-exercise beverage Water normally sufficient with slow fluid intake beginning at least 4hrs prior, if possible: 5-7ml/kg should be sufficient Sodium – stimulates thirst and retention of body weight Carbohydrates - Recommended additional intake of 3-5ml/kg-2hrs priors Hypohydration state prior to exercise Inadequate restoration of fluid from previous day’s exercise Multiple exercise bouts in hot and/or humid conditions Voluntary restriction of fluid to reduce body weight Amount & timing should be individualized Too little fluid intake: dehydration Too much fluid intake bloating Hydration strategy guided by: Intensity & duration of activity Potential effect of hypohydration on performance Environmental conditions Intake during training & performance Goals Replace body fluid Delay dehydration Replace sodium Avoid overconsumption and GI distress ACSM recommendations Marathon runners – 0.4-0.8l/h Drink or schedule w/ goal not to lose more than 2% of body weight Current Guidelines Develop a customized plan that considers sweat rate, sweat composition, duration, clothing, & environmental conditions Replenishment after training & performance Goals: Replace water loss, sodium and other electrolytes Plasma Na increases during exercise due to loss of water Consumption of adequate carb and protein Avoid GI distress Recommendations 1.5L/kg of body weight lost Na containing beverages: exercise for >4hr and heavy sweating Iv replacement: no evidence
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