Week 4 - Hydration Flashcards
What is the % of water in…
a) the adult body
b) lean body tissue
c) fat mass
a) 50-60%
b) 75%
c) 5-10%
What are the functions of water?
- Nutrient transport
- Protection
- Temperature regulation
- Biomechanical reactions
- Medium for reactions
Where is most of the total body water stored?
Intracellular fluid (62.5% of total body water) and extracellular fluid (37.5% of total body water - interstitial fluid and blood plasma)
Examples of fluid loss
- Exercise
- Respiration
- Skin
- Feces
- Urine
Examples of fluid gain
- Drink
- Food
- Metabolic
Euhydration
in fluid/water balance
Net body water balance
the difference between fluid water gain (intake + production) and fluid loss
Define dehydration (hypohydration) and how this can be indicated.
Dehydration is defined as a body water deficit greater than normal daily fluctuation. This can be indicated by a body mass loss >2%.
How can exercise-associated dehydration be defined?
This can be defined/indicated as an acute body mass loss of >2%.
What is the best static physiological index of hydration status?
the measurement of plasma osmolality (a measure of the total dissolved particle concentration)
- Typically 275-395 mOsm/kg
- Increase in this suggests dehydration.
Examples of dynamic assessments of hydration status before and after an exercise bout.
- Body mass change (in energy balance)
- Plasma osmolality (>5mmol/kg)
- Urine specific gravity (urine density relative to water (1.00), euhydrated at 1.003-1.035U)
How is the sweating response initiated during exercise in hot temperatures?
For every L of oxygen consumed 4kcal of heat is produced and most of this heat is passed to the body core.
Thermoreceptors senses increased in body and skin temperature (from 36-38 to 38-40 degrees C) and sends this to the hypothalamus.
This responds by increasing blood flow to the skin (vasodilation) and initiates sweating response. This cools body temperature and prevents hyperthermia.
For every L of oxygen consumed during exercise how many Kcal of heat is produced and where does this heat pass to?
4kcal and it passes to the body core
What is evaporative cooling? For every 1L of sweat evaporated, how many kcal of heat is removed from the body?
Evaporative cooling is where we remove heat from the body via sweat evaporation.
573kcal of heat from the body
Explain how water loss influences plasma and blood volume?
reduces plasma and blood volume because water loss is from the water component of blood (plasma).
How does sweat influence plasma osmolality?
it increases plasma osmolality - This is because sweat is hypotonic compared to plasma. When you sweat you lose more water but concentrations of sodium, glucose… remain high which increases plasma osmolality.
How may hypohydration impair performance when we have a BM loss of >2%?
1-2%: Minimal impact
2-3%
- Degrade aerobic performance
- Deterioration of sport-specific skills
- Minimal cognitive function impact (without heat stress) and reduced cognitive function (with heat stress)
> 3%: Impaired cognitive function
3-4%: Minimal impact on muscle strength and power.
What is the main mechanism by which hypohydration affects aerobic performance in warm/hot conditions?
Cardiovascular strain
- High skin blood flow
- Reduced blood volume
- Reduced oxygen delivery
- Reduced metabolite removal
What are the ACSM guidelines for hydration 2-4h pre-event?
5-10ml fluid/kg body weight
- Sodium, salt snacks or small meals may help
- More fluid if no/dark urine
Why is sodium beneficial…
a) pre-exercise
b) during exercise
c) post-exercise
a) Fluid retention
b) Limit electrolyte losses (risk of hyponatremia) and stimulate thirst
c) restoration of sodium and fluid balance
Why may adding sodium to a drink help with fluid retention?
it helps to maintain osmolality and reabsorption of water from kidney
What are the ACSM guidelines during exercise?
Sufficient fluid to limit body mass losses to <2% and limit excessive electrolyte imbalance.
- Typically, 0.4-0.8L/h of fluid
- Coolers drinks may help with thermoregulation + flavour can encourage voluntary consumption.
- Exercise >2h - add sodium to fluid
- Exercise >1h - may consider CHO addition
What are the ACSM guidelines post-exercise (rapid recovery and more recovery time)?
Rapid recovery (<12h) - consume 1.25-1.5L for each kg BM loss + sodium.
More recovery time - resume dietary practices + extra plain water.
How do you calculate sweat rate (liters per hour)?
Weight loss + volume consumed - urine loss / duration of exercise (hrs)
Weight loss = weight before - weight after
Volume consumed = bottle weight before - after
What should CHO-E (carbohydrate-electrolyte) solutions do?
- Supply CHO as the major energy source
- Be effective in maintaining hydration status
- Energy - 80-350kcal/L from CHO, >75% of energy from CHOs that induce high glycaemic response.
- Sodium: 20-50mmol/L (460-1150mg/L)
Hyponatremia
- What is it?
- What can it arise from?
- Who are at a greater risk?
- Low blood sodium - < 135mmol/L
- Can arise from over drinking fluids more than fluid losses (exacerbated with high sweat
sodium losses + low sodium
beverages) - Recreational athletes and women at greater risk.
How can we exacerbate hyponatremia?
exacerbated with high sweat
sodium losses + low sodium
beverages
What assessment tools can be used to determine hydration status in the 2-4hrs before an athlete starts exercise?
plasma osmolality and urine colour
Describe how you could develop an individualised plan for fluid consumption during exercise to minimise the risk of dehydration in an athlete.
Estimate sweat loss from pre-to-post exercise body mass change. Corrected for fluid consumed during exercise and urine produced.
