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Fluid and Electrolyte Replacement in Athletes

Fluid and Electrolyte Replacement in Athletes. Dr. David L. Gee FCSN/PE 446 Required readings: Williams: Chapter 9 (focus on p340-356) ADA/ACSM Sports Nutrition Position Paper. Korey Stringer 1974-2001 Minnesota Vikings Offensive Tackle. Water Balance: Normal.

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Fluid and Electrolyte Replacement in Athletes

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  1. Fluid and Electrolyte Replacement in Athletes Dr. David L. Gee FCSN/PE 446 Required readings: Williams: Chapter 9 (focus on p340-356) ADA/ACSM Sports Nutrition Position Paper

  2. Korey Stringer 1974-2001 Minnesota Vikings Offensive Tackle

  3. Water Balance: Normal

  4. Water Output:Normal vs.Exercise

  5. Water Intake: Normal vs Exercise

  6. In comparison to non-athletes: • Athletes greatly increase their water loss • Large increases in sweat loss • Some decreases in urine loss • Athletes need to greatly increase water intake • Large increases in fluid consumption • Smaller increases in food water and metabolic water • Athletes often fail to consume adequate amounts of fluids to maintain optimal hydration status

  7. Heat and Sweat Production During Exercise • 70kg subject, running 1 hr • 900 Cal expended • mechanical efficiency = 20% • 180 Cal movement, 720 Cal heat

  8. Heat and Sweat Production During Exercise • body specific heat = 0.83Cal/kg/deg • 780 Cal -> 12.4 deg C = 22 deg F • death

  9. Heat and Sweat Production During Exercise • Evaporate 1 liter sweat = • 580 Cal heat • 720 Cal heat = evaporates 1.24 liters of sweat • Real conditions, approx. 2 liters or 4.4 pounds of water loss

  10. Effect of Dehydration on Physiological Function • 2-4% wt loss - reduced muscular endurance time • 4-6% wt loss - reduced muscular strength & endurance, heat cramps • > 6% wt loss - severe heat cramps, heat exhaustion, heat stroke, coma, death

  11. Strategies for Avoiding Dehydration • NATA Position Statement: Fluid Replacement for Athletes • J. Athletic Training 35:212-224 (2000) • “Athletes do not voluntarily drink sufficient water to prevent dehydation during physical activity.” • Thirst is a delayed response to dehydration. Thirsty athletes are already dehydrated.

  12. Sports Nutrition Exam – Friday, May 5 • Format • multiple choice/true false • Short essay (2 – 2.5 pages) • Hypothetical case study • calculate exchange diet • Calculate fluid replacement needs • During exercise, after exercise (rehydration) • Bring calculator and pencils (no cell phone calculators) • Required readings • ADA/ACSM Position Paper: Sports Nutrition • Williams textbook

  13. Strategies for Avoiding Dehydration • Establish a hydration protocol for athletes • Determine individual sweat rate • Changes in body weight (pre-post weighings) • 1 pound = 1 pint additional fluids during exercise • May also account for urine volume • Goal: no weight loss (or < 2% wt loss) • Urine color or urine specific gravity

  14. Strategies for Avoiding Dehydration Emphasize continual fluid replacement • Replace fluids as they are lost • Practice fluid replacement • Gradually increase fluids • Body adapts to increase fluid consumption • Generally, cold fluids more rapidly absorbed • Use individual clear bottles for visual monitoring • Old Rule of Thumb: • 0.5-1 cup per 10-15 min • Individualize is far better

  15. Strategies for Avoiding Dehydration • Understand each athlete’s sport dynamics • Rest breaks/time outs • Fluid accessibility • Establish athlete’s acclimatized state • Non-Acclimatized athletes • sweat more • lose more electrolytes

  16. Strategies for Avoiding Dehydration • Anticipate high risk conditions • High temperature • Uniform/clothing effects • High humidity • Indoor sports • Uniform/clothing effects • Low air movement • Uniform/clothing effects • Bright sun • Dark colored clothing

  17. Strategies for Avoiding Dehydration • Hyperhydration • 1 pint, 15-30 minutes prior to exercise • Limited benefits • Post-exercise rehydration • Ideally completed within 2 hrs • 1 pound wt loss = 1.5-2 pts fluid replacement • ACSM/ADA rec: 16-24 oz per pound weight loss • 1-1.5 pts per pound weight loss • Replace CHO and electrolytes at same time to speed rehydration

  18. Calculating hydration needs • Hydration Worksheet • Available on course web page

  19. Example: • Joe played tennis for two hours. He drank a 16oz bottle of water during his workout. • Initial weight = 180 lbs • Post-exercise weight = 176 lbs • Water loss = 180-176 = 4 lbs • % body weight loss = 4/180 = 2.2% (dehydrated) • Total sweat loss = 4 pts + 1pt = 5 pts = 80 oz • To stay hydrated within 2% (minimum fluid replacement rate) • 2% x 180 = 3.6 lbs allowed wt loss = 3.6 pts allowable sweat loss • 5 pts – 3.6 pts = 1.4 pts = 22.4 oz • 22.4 oz/120 min = 0.19 oz/min = 2.8 oz every 15 min • Maximum fluid replacement rate • 80 oz / 120 min = 0.67 oz/min = 10 oz every 15 min • Recommended fluid replacement (per 15 min) • 2.5-10 oz every 15 min

  20. Practice Hydration Problem • LeBron participates in a 90 minute basketball workout each day. • Pre-workout weight = 240 lbs • Drinks 8 oz during workout • Post-workout weight = 234 lbs • To avoid dehydration and overhydration, how much fluid should LeBron consume during his next workout?

  21. Practice Problem Solution • Weight loss = 240-234 = 6 lbs (pts) • % weight loss = 6/240 = 2.5% (dehydrated) • Total sweat loss = 6pts + 0.5pts = 6.5pts = 104 oz. • Allowable sweat loss = 2% x 240 = 4.8 lbs • Minimum fluid replacement = 6.5 – 4.8 = 1.7 pts = 27.2 oz • 27.2 oz/90min = .30oz/min x 15 = 4.5 oz/15min • Maximum fluid replacement = 104oz/90 = 1.15 oz/min x 15 = 17 oz/15min • Rec Intake ~ 4-16 oz/15min

  22. Electrolyte Replacement • Sweat from extracellular fluids • Major electrolytes are Na and Cl • Potassium and calcium are minor components • Sweat is hypo-osmolar (hypotonic) compared to plasma • Dehydration (with no/limited fluid replacement) leads to hypernatremia • Williams: “Thus, electrolyte replacement during exercise is not necessary.”

  23. Electrolyte Strategies for Athletes • Most athletes do NOT need additional electrolytes • Exception is for very high sweat losses (> 1hr or heat stress conditions) • Replacement with excessive amounts of pure water can lead to hyponatremia (water intoxication) • Dizziness, fainting, seizures, death • Swelling of the brain • Or asymptomatic • Symptoms mimic dehydration • Lack of ability to spit, dry skin, high body temperature indicates dehydration

  24. Prevalence of Hyponatremia in Elite Athletes • 1999 New Zealand Ironman Ultradistance • 18% of finishers were hyponatremic • 45% female finishers hyponatremic • 14% male finishers hyponatremic • Adequate water intake • but inadequate electrolyte replacement • 2002 Boston Marathon • 13% with hyponatremia • 0.6% with critical hyponatremia (3 runners)

  25. Hyponatremia Common Causes • excessive fluid consumption • excessive sodium loss in sweat • excessive sweating • “salty sweaters” • Risk Factors • heat stress environment • long duration • slower athletes • non-acclimatized athletes • small body weight (females)

  26. Hyponatremia: Key Points • Hyponatremia unusual compared to prevalence of dehydration • Know risk factors/situations • Watch out for ‘too much of a good thing’ • fluid intake should not exceed losses • Sodium content of sport drinks are useful in preventing hyponatremia • Sodium concentration in sports drink is more dilute than in sweat • Palatability issues

  27. Electrolyte replacement after exercise • Electrolyte imbalances can occur with: • Low salt intake • Repeated days of hard training • 4 liters of sweat contains 3-7g sodium • Additional losses in urine, stools • Average US intake 6-9g sodium • Increase sodium consumption • salty foods • Salt (2g Na/tsp) • Salt tablets (during acclimatization, 1-2 wks)

  28. Sport DrinksWater, CHO, electrolytes replacement during exercise • Provide water • Provide dilute carbohydrates • should be < 10% (<8% optimal) • Gatorade: G+S @ 6% • Powerade: F+GP @ 8% • Fruit juice: F+S @ 11-15% • Soft drinks: F @ 11%

  29. Carbohydrates in Sport Drinks • Glucose • rapidly absorbed and utilized by muscle • Fructose • more slowly absorbed and utilized by liver to replace liver glycogen • Sucrose (G-F) • Glucose Polymers • lower osmolarity than simple sugars and may allow for more rapid water absorption

  30. Sport Drinks • Provide electrolytes during exercise • replace Na and Cl lost in sweat • enhances water uptake • [NaCl] < 1000mg/L • Gatorade: Na,Cl,K,P (460mg/L) • Powerade: (Na,Cl) (300mg/L) • Orange Juice: (10 mg Na/L) • Soft drinks: (40 mg Na/L)

  31. Sport Drinks • Preferred tastes • Especially kids/teens • Particularly useful for: • endurance athletes • high heat stress environments • heavy sweaters

  32. Specialty Sports Drinks • Gatorade Endurance Formula • Nearly double sodium content + other electrolytes • May be beneficial for athletes at risk for hyponatremia • Gatorade Propel • Dilute (3g CHO), “vitamin enhanced”, electrolytes ? • Flavored drinks may be more readily consumed

  33. Homemade Sport DrinkNancy Clark’s Sport Nutrition Guidebook, 2nd ed. • Yield: 1 quart • 4 Tbl sugar • 1/4 tsp salt • 1/4 c boiling water • 1/4 c orange juice (not concentrate) or 2 Tbl lemon juice • 3 3/4 c cold water • dissolve sugar,salt in hot water, add juice & cold water, chill • 50Cal, 12gCHO, 110mgNa, 30mgK per cup

  34. Homemade Sport DrinkHilary Warner, Nutrition Works! • 2/3rd cup lemonade mix • 2.25 quarts water • ¼ - ½ tsp salt • 8oz contains • 65 Cal • 15g CHO (6%) • 65-130 mg Na

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