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 Stringer1974-2001

Minnesota VikingsOffensive Tackle

Water Balance: Normal

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Output Intake

MetabFoodFluidsStoolBreathSweatUrine

Water Output:Normal vs.Exercise

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Normal Exercise

StoolBreathSweatUrine

Water Intake: Normal vs Exercise

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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

Heat and Sweat Production During Exercise

70kg subject, running 1 hr900 Cal expended

mechanical efficiency = 20%180 Cal movement, 720 Cal

heat

Heat and Sweat Production During Exercise

body specific heat = 0.83Cal/kg/deg

780 Cal -> 12.4 deg C = 22 deg F

death

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

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

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.

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

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

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

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

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

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

Calculating hydration needs Hydration Worksheet

Available on course web page

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

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?

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

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.”

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

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)

HyponatremiaCommon 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)

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

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)

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%

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

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)

Sport Drinks Preferred tastes

Especially kids/teens

Particularly useful for: endurance athletes high heat stress environments heavy sweaters

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

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

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