Hydration

HYDRATION

WATER BASICS AND WATER BALANCE

  • Water Characteristics:

    • Does not provide energy (0 kcal).

    • Essential for maintaining life.

    • Functions include:

    • Delivery of nutrients and removal of waste.

    • Acts as a reactive medium and solvent.

    • Maintains body temperature through cooling mechanisms.

    • Maintains pH balance.

    • Maintains blood volume.

  • Water Composition in the Body:

    • Composition range of total body water (TBW): 50-70% of total body weight.

    • TBW can be estimated as:
      TBW=0.73×fat free massTBW = 0.73 \times \text{fat free mass}

  • Factors Affecting Hydration:

    • The amount of water in the body is influenced by:

    • Body size.

    • Gender.

    • Age.

    • Body composition.

  • Total Body Water Estimation:

    • Total body water is approximately 42 liters:

      • Intracellular water: ~28 liters (about 2/3 of TBW).

      • Extracellular water: ~14 liters, comprising:

      • Interstitial fluid: ~11 liters.

      • Plasma: ~3 liters.

ELECTROLYTE BALANCE

  • Milliequivalents per liter of water (H₂O):

    • Major electrolytes distributed across different compartments:

    • Extracellular (Plasma, Interstitial) and Intracellular fluid compartments with key cations and anions detailed.

    • Examples include:

      • Na+Na^+ (sodium), K+K^+ (potassium), HCO3−HCO_3^- (bicarbonate), Cl−Cl^- (chloride).

ASSESSING HYDRATION STATUS

  • Water Intake and Output:

    • Water Challenges throughout the day: Promotions to encourage hydration at specific hours (e.g., Good Morning, Remember your Goals, etc.).

    • Hydration from food sources:

    • Meats like chicken, beef, pork, fish contain 50-80% water.

SENSIBLE WATER LOSSES

  • Loss mechanisms:

    • Urination (~60% of water loss at rest; ~500-1000 ml).

    • Defecation (100-200 ml).

    • Sweating, especially during exercise in warm temperatures, can lead to losses of 450-1900 ml.

INSENSIBLE WATER LOSSES

  • Perspiration (~15%):

    • Includes ventilation and non-sweat diffusion, often unnoticeable except in cold conditions (visible breath).

DIET AND FLUID LOSS

  • Diet impacts hydration:

    • Diuretics: Coffee and alcohol lead to increased water loss:

    • Lose ~1 ml water for every mg of caffeine consumed.

    • High protein diets and certain medications can influence hydration negatively.

VARIABILITY IN SWEATING RATE

  • Factors that influence sweating include:

    • Exercise intensity.

    • Body size.

    • Environmental conditions (temperature, humidity, wind).

    • Heat acclimation and clothing.

    • Individual factors (body composition, sex, age, genetics).

    • Heavy vs light sweaters, with sweat rates ranging from 0.5 to 2.0 L/h.

SWEAT COMPOSITION

  • Concentration of electrolytes in sweat (mmol/L):

    • Sodium: 10-90

    • Chloride: 10-90

    • Lactate: 5-40

    • Urea: 4-12

    • Potassium: 2-8

    • Ammonia: 1-8

    • Other components include bicarbonate, calcium, magnesium, glucose, amino acids, iron, copper, zinc (all < 1).

    • Sodium loss to potassium occurs in a typical ratio of 3:1 to 5:1.

SODIUM LOSS AND REPLACEMENT

  • Sodium loss potential:

    • Can lose up to 1610 mg of sodium via sweat.

    • Hydration strategies based on exercise duration:

    • For <2h of exercise: Replace water.

    • For >2h of exercise: Replace sodium as well.

SODIUM AND POTASSIUM SOURCES

  • Sodium sources:

    • Pretzels, chips, sandwiches, nuts, sports drinks (1 serving = 300-1,000 mg of sodium).

  • Potassium sources:

    • Fruits, vegetables, beans.

    • Hypokalemia is defined as levels < 3.5 mmol/L; however, it is very rare.

CONSEQUENCES OF POOR WATER BALANCE

  • Hydration Imbalances:

    • Dehydration: Occurs when water loss exceeds intake, resulting in a negative balance.

    • Consequences of dehydration:

      • Reduced blood volume leading to hypovolemia.

      • Increased blood viscosity.

      • Reduced stroke volume and cardiac output, increased heart rate and core temperature.

    • Impaired physiological performance:

      • Increased muscle glycogen usage.

  • Hydration Levels and Performance Impairment:

    • Thirst, loss of appetite, nausea, and confusion increase with % body weight loss:

    • 1%: Thirst

    • 2%: Thirst, loss of appetite

    • 3%: Impatience, decreased blood volume

    • 4%: Nausea, slowing of physical work

    • 5%: Difficulty concentrating

    • 6%: Increased body temperature, pulse, breathing rate

    • 7%: Stumbling, headache

    • 8%: Dizziness

    • 9%: Weakness, mental confusion

    • 10% +: Muscle spasms, kidney failure, poor circulation.

DEHYDRATION AND PERFORMANCE

  • Performance declines with varying levels of dehydration:

    • For example, a loss of 2% of body weight may result in slower movement accuracy in basketball, decreased performance in distance cycling, and increased running times.

DEHYDRATION AND CRAMPING

  • Exercise-associated muscle cramping (EAMC):

    • Caused by dehydration and electrolyte loss, which leads to altered neuromuscular control and fatigue.

    • Heat cramps result from dehydration coupled with sodium depletion.

HYPERHYDRATION

  • Defined as overdrinking water or low-sodium liquids leading to hyponatremia:

    • Characterized by dilution of plasma sodium concentrations to <135 mmol/L, risk is higher for endurance athletes.

HYPONATREMIA

  • Symptoms resemble those of intoxication:

    • Include muscle weakness, incoordination, disorientation, and potentially severe outcomes like seizures or death.

    • Prevention measures include ingesting electrolyte-containing sports drinks.

ASSESSING HYDRATION STATUS

  • Methods of monitoring hydration:

    • Body weight assessment before and after practice (1 lb lost = 2-3 cups of water).

    • Urine color chart for assessing hydration:

    • Pale lemonade/clear indicates positive balance; darker colors indicate negative balance.

    • Monitoring urine volume and frequency:

    • Urination every 1-2 hours is ideal.

HYDRATION RECOMMENDATIONS

  • Daily Intake Recommendations based on age and gender:

    • AI from food (L/day), AI from fluid (L/day), and total AI:

    • Females >19 y/o: 0.5, 2.2, 2.7 L/day

    • Males >19 y/o: 0.7, 3.0, 3.7 L/day

    • Variations based on age group, especially for young adolescents.

  • General guideline: 1 ml of water for every kilocalorie consumed. Example:

    • 3,000 kcal = 3,000 ml (~101 oz or ~13 cups).

  • Factors influencing recommended higher intake:

    • Body size, training demands, and weather conditions.

PRACTICAL GUIDELINES FOR HYDRATION

  1. Athletes must be aware of their recommended intake.

  2. Urination should be stimulated every 1-2 hours.

  3. Urine color should be light lemonade.

  4. Hydration sources include water, milk, juice, sports beverages, fruits, etc.

  5. Moderate caffeine and limit alcohol for effective hydration.

  6. Increase water intake when on a high protein diet.

PRE-EXERCISE HYDRATION

  • Importance: Hyperhydration enhances performance setup.

  • Recommended hydration method:

    • Consume ~5-7 ml/kg with sodium approx. 4 hours before exercise, and an additional 500ml (17 oz) 2 hours prior.

  • Hydration Sources and Effects:

    • Water: Easy access but may cause GI distress.

    • Juice: Carbohydrate and electrolyte content, absorbed quickly but may cause distress if high fructose.

    • Sports Drinks: Preferred for training.

HYDRATION DURING EXERCISE

  • Goals include maintaining plasma volume, electrolyte balance, core temperature, heart rate, and delaying fatigue.

  • Hydration varies with:

    • Body size, exercise intensity, environmental conditions, etc.

  • A general guideline is to consume ~4-6 oz every 20 minutes.

ENDURANCE CAPACITY

  • Effect of hydration on running endurance at a temperature of 20 °C (68 °F).
    .

CALCULATING FLUID NEEDS

  • Step 1: Calculate body weight loss before and after exercise.

    • Alex weighed 145 lbs pre-exercise and 143 lbs post-exercise:

    • Weight loss = 145 lbs - 143 lbs = 2 lbs (equivalent to water loss).

  • Step 2: Calculate fluid equivalent for weight loss.

    • Fluid equivalent = weight loss × 16-24 oz = 2 lbs × (16-24 oz) = 32-48 oz.

  • Step 3: Determine total fluid need:

    • Alex consumed 20 oz during training.

    • Total fluid need = oz consumed + oz lost = 20 oz + (32-48 oz) = 52-68 oz.

TYPES OF FLUIDS DURING EXERCISE

  1. Water: Basic hydration.

  2. Carbohydrates: For prolonged exercise (>60 minutes); consume 30-60 grams/hour in a 6-8% carbohydrate solution to avoid GI issues.

  3. Electrolytes: Essential for prolonged, endurance athletes—especially in hot conditions (sodium and chloride).

POST-EXERCISE HYDRATION

  • Goal: Replace lost water, carbohydrates, and electrolytes effectively.

  • Guidelines for rehydration include:

    • Rehydrate immediately and maintain consistency in fluid intake.

    • For every pound lost, consume 16-24 oz of fluid.

    • Include sources such as fruit juices, soups, and sports drinks.

SUMMARY OF HYDRATION RECOMMENDATIONS

  • Daily Recommendations Before and After Exercise:

    • 2-4 hours prior: 3.7 L/day (M), 2.7 L/day (F)

    • 10-20 minutes prior: 13-20 oz.

    • During exercise: 7-10 oz every 10-20 minutes.

    • Post-exercise: 16-24 oz for every lb of body weight lost, consumed within 2 hours.

    • Types of beverages recommended include water, 100% juices, milk, and sports drinks.