Hydration and Sports Drinks

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Hydration and Sports Drinks
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Heat Removal

• Exercise increases core temperature.
• For every L of O2 consumed during
• exercise 5 kcal is produced but only
• 1kcal is used for mechanical work the
• rest is heat
• Increases in core temperature
• Increase blood flow to the skin
• Initiate sweating

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Sweating and Fluid Loss

• Mild to moderate work and routine physical
  training typically result in whole-body sweat
  losses of about 0.8-1.4 L/h.
• Evaporation of 1L of water from the skin will
  remove 573 kcal of heat from the body.
• Heat loss via evaporation of sweat is largely
  dependent on the humidity (proximate to the skin)
  in which the athlete is working.
• Individual sweat rates and fluid losses vary
  widely between athletes and across sports.

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Dehydration and Performance

• If sweating is not compensated for with fluid
  intake performance is affected.
• Dehydration may explain some of the fatigue at
  the end of a long sporting event.
• Exercise performance is impaired by a fluid loss
  of 2 (this is 1.5L in a 155lb male athlete),
  Losses in excess of 5 can decrease work capacity
  by 30 (water weight loss of 8lbs)

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In cool laboratory conditions, VO2max has been
shown to decrease with fluid losses gt 2 BW...
In the heat, sweat rates increase even more such
that fluid intake must be even more closely
monitored.
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Exercise Capacity
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Body weight loss ()
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How does sweating (fluid loss) work to decrease
performance?
increase in plasma osmolarity (higher
concentration of solute in solution)
release of vasopressin (ADH) from the posterior
pituitary gland.
ADH causes the kidney to re-absorb water
Urine volume goes DOWN dramatically to preserve
blood osmolarity, volume and pressure
As exercise progresses, the transfer of body
water into the plasma cannot keep up with sweat
losses so...performance decreases.
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How can I tell how much Im sweating?

• Pre exercise weight 55 kg
• Post-exercise weight 53.5 kg
• Volume of fluid consumed during exercise 1 kg
• Exercise duration 2 h
• Calculations
• Fluid deficit (L) 55 kg 53.5kg 1.5 kg
• Total sweat loss (L) 1.5 kg 1 kg 2.5 kg
• Sweat rate (L/h) 2.5 kg / 2hr 1.25 L/h

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Hydration Rehydration
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• Urine Color Chart
• Assess Hydration
• 1, 2, or 3 Well Hydrated
• 7 or Darker Dehydrated

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Daily Water Balance

• Athletes need to be fully hydrated before
  training/competition
• The average sedentary person excretes about
• 2700 milliliters of water/day (1400 from urine,
  1100
• sweat/breath)
• To replace that 2700 ml, get
• 300-400 ml from metabolism,
• 1000 ml from food and
• 1300-1400 ml from beverages
• 2700 ml

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Athletes and Daily Water Balance
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Athletes and Fluid Intake

• Athletes have to consider their daily water
  balance and sweat loss during exercise when they
  construct a hydration plan.
• Choices to maintain/increase fluid intake
• Water
• CHO Drinks (carbohydrates of the form CxHyOz)
• Choc Milk
• Coca-Cola

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• The maximum amount of fluid that empties from the
  stomach during exercise is 0.8-1.2 L/h.
• Remember, sweating during exercise can cause
  fluid losses of 0.8-1.4l/hr
• Up to 10 CHO solution empties from the stomach
  at the same rate as pure water (Coke is 11)
• Glucose and sodium both stimulate the absorption
  of fluid across the membrane of the small
  intestine.

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• Athletes should consume enough water throughout
  exercise that their weight remains constant (if
  possible)
• Guidelines for fluid intake are VERY general due
  to the variability of sweat rates among
  individuals.
• Good rule of thumb is to consume something every
  fifteen minutes (8-12 oz.)

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  ACSM NATA AIS Gatorade NCAA
Before 500 ml 2 hours 500-600 ml 2-3 hours Ind 17 - 20 oz 2 to 3 hours 17 - 18 oz 2 hours
200-300 ml 10-20 min 7-10 oz 10 - 15 pre warm-up

During Regular Intervals 200-300 every 10-20 min Ind 7-10 oz every 10-15 min 8 oz every 10-15 min

After Equal to loss 150 of weight lost Ind 20-24 oz / lb 20-24 oz / lb

Temp 59o - 72o F 50o - 59o F Ind Cooled 50o - 59o F

Contents CHO and Sodium CHO and Electrolytres Ind CHO (6-7) and Sodium -
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After Exercise

• Drink 150 of water weight loss to achieve normal
  hydration 6hrs post-exercise
• (this accounts for reduced urine output)
• Pure water may not be the ideal recovery drink
• Causes rapid fall in plasma sodium and thus
  plasma osmolarity which reduce the stimulation to
  drink and also increases urine output. This can
  delay the re-hydration process

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• What to drink then?
• Plasma volume is rapidly restored if some sodium
  chloride is added (77mol or 0.45g/L)
• Sodium
• Helps maintain thirst, delays urine production
• Potassium
• Thought to promote intracellular hydration
  (little evidence to support this, but it sounds
  good)
• CxHyOz (glucose, glucose polymers)
• More likely to continue drinking fluid if
  beverage is sweetened (taste) vs. pure water
• Presence of glucose stimulates fluid absorption
• We know it helps with muscle glycogen
  re-synthesis

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CHO Sports Drinks

• The goal of the carbohydrate (CHO) content is to
  provide the appropriate CHO concentration while
  preventing gastrointestinal disturbances.
• At 6-8 carbohydrate concentration, sports drinks
  have can be absorbed 30 faster than water.
• The composition of the carbohydrates in sports
  drinks is another variable that affects the
  effectiveness of the drink
• The 3 things a sports drink should accomplish
• Hydrate effectively.
• Replenish electrolytes.
• Provide energy for working muscles to enhance
  performance and speed recovery.

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Gatorade

• Gatorade
• 6 Carbohydrate-electrolyte solution.
• 14 g of CHO (sugar) in 8 fl oz.
• 110 mg of Na in 8 fl oz.
• 30 mg of K in 8 fl oz.
• 90 mg of Cl- in 8 fl oz.
• Retail Price 1-2.

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Powerade

• PowerAde
• 7 Carbohydrate-electrolyte drink.
• 18 g of CHO in 8 fl oz with 15 g as sugar.
• 53 mg of Na in 8 fl oz.
• 34 mg of K in 8 fl oz.
• Retail Price 1-2.

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Flavored Water

• Propel Fitness Water
• Calories 10 in 8 fl oz.
• Sodium 35 mg
• Potassium 40 mg
• Total Carbohydrate 3 g Sugars 2 g
• Vitamin C 10
• Vitamin E 10 Niacin 25
• Pantothenic Acid 25
• Vitamin B12 4
• Vitamin B6
• Retail Price 1.25 per bottle.

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• From the textbook to the track
• Dont wait until thirsty... Thirst signal is the
  result of being slightly dehydrated.
• Monitor urine output and weight before and after
  exercise (approximate fluid loss)
• In hot weather athletes need to consume more
  fluid during/after exercise compared to colder
  weather.
• For recovery, supplement with a carbohydrate
  drink that contains some sodium to aid in
  replenishment of glycogen stores and
  electrolytes. (remember the protein)... Gatorade,
  Choc milk or coke?