Chapter 9: Water Requirement and Fluid Balance Lecture 6.1

1. Chapter 9:Water Requirement and Fluid BalanceLecture 6.1

2. Fluid Requirements for Athletes • Athletes must be fully hydrated before they train or compete • Cannot adapt to dehydration • Performance will diminish as the athlete becomes dehydrated during competition

3. Ensuring Adequate Hydration Before Exercise • Adequate hydration can be accomplished in the last few days leading up to competition • Methods to check: • Urine should be pale in color - not reliable as athletes may be taking supplements that contain B vitamins that color urine yellow • Measuring urine osmolality – most reliable • > 900 mOsmol/kg – dehydrated • 100 – 300 mOsmol/kg – well hydrated • Measuring body weight after rising before and after voiding – moderately reliable • Sudden drop in body mass any given day can indicate dehydration

4. Ensuring Hydration During Exercise • Thirst • Relying on thirst as a signal to drink is unreliable • Dehydration can occur before the thirst sensation • Goals • Consume enough fluids to keep body weight constant before and after • Athletes need to acclimatize to drinking and regular intervals during exercise • American and Canadian Dietetic Associations recommendations • Before Exercise: 15 minutes before consume ~ 500 ml of fluid • Hot and humid environments: frequent consumption, every 15 to 20 minutes of small volumes of 120 – 180 ml • Exercise lasting between 30 – 60 minutes water is sufficient to maintain hydration

5. Fluid Ingestion During Exercise • Benefits • Supplies exogenous fuel substrate – usually in the form of carbohydrates • Helps maintain plasma volume • Prevents dehydration • Gastric emptying • Availability of fluids ingested is limited by the rate of gastric emptying (intestinal absorption) • The faster gastric emptying = decreased absorption • Addition of carbohydrates to fluids decreases gastric emptying = increased absorption

6. Water Absorption in Small Intestine • Osmosis • Promoted by coupled transport of glucose and sodium

7. Composition of Sports Drinks • Dependent upon relative needs to replace water and provide fuel substrate • Main goal is rehydration i.e. heat • Carbohydrate (i.e. glucose) = 20-60 g/L • Sodium = 20-60 mmol/L • Not exceed isotonicity of 290 mOsmol/L • Substrate provision to maintain endurance i.e. cooler environment • Carbohydrate (i.e. glucose polymers) = 100-150 g/L • Gastric emptying can be minimized by adding glucose polymers • Minimize osmolarity • Keep volume of the fluid in stomach as high as is comfortable for the athlete

8. Composition of Sports Drinks cont. • Commercially available sports drinks • Carbohydrate (i.e. glucose, glucose polymers, and some fructose) = 60-80 g/L, • Sodium = 20-25 mmol/L • Ideal fluid Replacement • Tastes good • Does not cause GI discomfort when consumed in large volumes • Promotes rapid gastric emptying and fluid absorption to maintain extracellular fluid volume • Provides energy in the form of carbohydrates for working muscles • Presence of sodium promotes consumption by maintaining thirst

9. Jeukendrup, Gleeson. Sport Nutrition: An Introduction to Energy Production and Performance 2e. Human Kinetics Inc, 2010.

10. Drinking During Training • Often neglected • Practice will accustom athletes to feeling of fluids in the stomach • Opportunity to experiment with different volumes and flavorings • Measure fluid consumption and body mass changes before and after • Provides an idea of athlete’s sweat rate under different environmental conditions • Help determine athlete’s requirement for fluid intakes during competition

11. Rehydration after Exercise • Progressive Dehydration with repeated bouts of exercise • Imparied thermoregulation • Increased cardiovascular strain • Loss of thermoregulatory advantages conferred by heat acclimation and high aerobic fitness • Loss of intracellular and extracellular volume during recovery • Reduced intracellular volume reduces rates of glycogen and protein synthesis • Main factors influencing effectiveness of postexercise rehydration • Volume and composition of fluid consumed

12. Sodium in Sports Drink • Major cation in intracellular fluid • Euhydration is achieved when sodium intake is greater than sodium loss (Schirreffs et. al, 1996) • Promotes rapid fluid absorption in small intestine • Allows plasma sodium concentration to remain elevated during rehydration proces • Maintains thirst • Delays stimulation of urine output

13. Potassium in Sports Drink • Enhance replacement of intracellular water • Promote rehydration • Further studies need to be done to confirm hypothesis

14. Optimal Rehydration Beverage • Carbohydrates • Glucose • Glucose polymers • Stimulates fluid absorption in stomach

15. Fluid Consumption Post Exercise • Post Regular Exercise • Any fluid deficit incurred during one exercise can compromise the following exercise session • Ingestion of 150 % of weight loss for every kilogram of weight loss during exercise • Intake of caffeine and alcohol is discouraged • Diuretic actions • Consume solid fluids • Replace sodium and potassium losses

16. Recommendations on Exercise and Fluid Replacement • American College of Sports Medicine Guidelines on Fluid Intake for Exercise (2002) • Adequate fluid replacement maintains hydration and promotes health, safety and optimal performance • Consume a nutritionally balanced diet and drink adequate fluids 24 hours before an event • Consume approximately 6-8 ml of fluid per kg of body weight about 2 hours before exercise

17. Recommendations on Exercise and Fluid Replacement Cont. • During exercise drink early and at regular intervals to prevent excesses of 2 % of body weight • Fluids consumed should be below ambient temperature • Add carbohydrates and sodium when exercising longer than 60 minutes • Exercise bouts > 60 minutes • Add carbohydrates at a rate of 30-60 g/hour to maintain oxidation of carbohydrate and delay fatigue

18. Recommendations on Exercise and Fluid Replacement Cont. • Addition of sodium during exercise bouts lasting > 60 minutes • 500 – 700 mg/L water • Enhance palatability • Promote fluid retention • Prevent hyponatremia (in people who drink excessive amounts of fluid during prolonged exercise) • Rapid recovery from excessive dehydration • 1.5 L of fluid for each kilogram of body weight loss • Addition of sodium will assist rapid and complete rehydration by stimulating thirst and fluid retention