Lecture 4: Hydration Flashcards
Old recommendation for amount of water to drink
1 mL/kcal consumed
New DRI for fluids (assumed normal activity)
- 7 L/day for men
2. 7 L/day for women
__% of fluid intake can come from food
20%
Functions of fluids
- Delivers nutrients
- Removes waste
- Lubricates joints
- Medium for chemical reactions
- Blood volume
- Absorption & release of heat
__% of the human body is made up of water
50-60%
__% of muscle tissue is water
70%
Storage of water in comparison to glycogen
1 g glycogen stored = 3 g water stored
Most important function of fluids. Why?
Absorption and release of heat. Water conducts heat 26x faster than air.
Ways to dissipate heat (humans)
1) Conduction
2) Convection
3) Radiation
4) Evaporation
What is the least efficient way to transfer heat? Most efficient?
Radiation;
Evaporation
Factors affecting sweat rate
- Air temp
- Humidity
- Wind
- Clothing / equipment worn
- Heat acclimatization of athlete
- Genetics
- Fitness of athlete
- Type of activity
How much water loss is considered dehydration?
> 2% body weight
Dehydration symptoms
- Decreased athletic performance
- Decreased cognitive function
- Decreased ability to regulate heat
- Cardiac drift
Define: cardiac drift
Increased heart rate in the absence of exercise intensity; results from loss of blood volume.
Venn diagram to access dehydration
- Weight
- Urine colour
- Thirst
Water weight fluctuation = __% of body weight
1%
American College of Sports Medicine recommend what kind of water intake to avoid dehydration?
- 400-600 mL 4 h before exercise
- 3-5 mL/kg 2 h before (no or dark urine)
- 200-300 mL 20 min before
Who might tolerate dehydration better: runner or cyclist? Why?
Cyclist
- Goes faster, so there is more wind
- Wind cools you down, so even without sweat you stay cool
- Staying cool also means you sweat less -> less water loss
What is the term used to describe drinking too much fluids during exercise?
Exercise-associated hyponatremic encephalopathy (EAHE)
Define: hyponatremia
A disorder of fluid / electrolyte imbalance that results in abnormally low sodium concentrations (< 135 mmol/L) typically occuring during endurance activities lasting longer than 4 hours
Normal sodium concentration in the body
135 mmol/L
Who is at higher risk for hyponatremia?
- Non-athlete
- Small frame
- Higher amount of fat
- Slow running
- Drinks excessively
Functions of sodium
- Nerve impulse transmission
- pH balance
- Blood pressure
Physiological range of sodium
0.4 ~ 1.6 g/L
Sodium concentration in sweat
50 mmol/L or 1 g/L
Na is found ___ the cell; K is found ___ the cell.
Na = outside; K = inside
Function of potassium
- Nerve impulse transmission
- Muscle contraction
Requirement of K intake (AI)
4700 mg/day
Electrolytes lost in sweat
- Na (major)
- K (major)
- Cl
- HPO
- Mg
- Fe
Max urine output
1 L/h
When is it okay to “drink when thirsty”?
- Women
- Light weight
- Cold weather
- Slow pace
- Ample opportunity
When should you have a hydration plan?
- Men
- Heavy weight
- Hot weather
- Fast pace
- Limited opportunity
Best CHO % for absorption
6-8% concentration
How many grams of CHO can humans metabolize per hour?
30-60 grams/h
What is the major limiting factor in CHO absorption?
Saturation of intestinal transporters
How to increase CHO absorption?
Eat multiple transportable carbohydrates (combination of different CHO) – use different transporters so saturation occurs much later.
How many grams of multiple transportable CHO can humans metabolize per hour?
> 100 grams/h
Multiple transportable CHO may be useful for what type of athletes?
Athletes involved in endurance sports (3 or more hours)
When is it okay to drink sport drinks > water?
When exercising for > 1 h (especially if results matter)
Gatorade company is an example of… (what fallacy)?
false cause
