Hydration Part 1 W4 Flashcards
What is total body-water volume within the body?
42L
60% of body mass
What is body water like in adults?
a) Lean body tissues
b) Fat mass
a) 75% water
b) 5-10% water
What are the functions of water?
Nutrient transport
Protection
Temperature regulation
Biochemical reactions
Medium for reaction
What is euhydration?
Normal state of body water content
How is fluid lost in the body (2200ml)?
Respiration= 200ml
Skin= 600ml
Feces= 100ml
Urine= 1300ml
How is fluid gained in the body (2200ml)?
Drink= 1200ml
Food= 700ml
Metabolic= 300ml
What is net body water balance?
The difference between fluid water gain (intake production) and fluid loss
Challenged during period of high sweat rates
What is dehydration?
Referred as hypohydration
Defined as a body water deficit greater than normal daily fluctuation
What is the most sensitive and simplest measure to determine acute body changes in body water?
Changes in body mass
What does acute 2% body mass reduction cause?
90% chance that body water deficits are sufficient to be classed as dehydration
What is osmolality?
A measure of the total dissolved particle concentration (in mOsm/kg)
What is the best static physiological index of hydration status?
Measurement of plasma osmolality
What is the typical values of osmolality?
275-295 mOsm/kg
What happens when the value of osmolality surpasses 295 mOsm/kg?
Its an indication of dehydration
How can dynamic dehydration assessment be tracked?
Body mass change (in energy balance)
Plasma osmolality
Urine specific gravity
What is urine specific gravity?
Urine density relative to water = 1.00
You are euhydrated at 1.003=1.035 U(Eu)
What is the bodies core temperature?
a) Normal body temperature
b) Exercise
a) 36-38degrees
b) 38-40degrees
What senses an increase in body/skin temperature?
Hypothalamus
How does the hypothalamus respond to increase body temperature?
Responds by increasing blood flow to skin and initiates sweating response
Why do we sweat?
Evaporative cooling
Heat production for execrise
What will evaporative cooling result in?
1L sweat evaporated will remove 573kcal of heat from the body
What type of drinking during periods of sweat will lead to body water deficit?
Ad Libitum drinking
What are components of sweat?
Sodium
Chloride
Potassium
Lactate
What is plasma sodium normally?
135-145mmol/L
What is sweat?
Hypotonic
What does hypotonic mean?
Having a lower osmotic pressure than a particular fluid
How does sweat loss cause reduced plasma and blood volume?
Water loss from the water component of blood (plasma)
Why does sweat loss cause an increase in plasma osmolality increase?
Due to sweat being hypotonic
What are the main mechanisms that control body temperature during exercise (therefore preventing hyperthermia)?
Sweating
Evaporative heat loss
What does dehydration depend on?
Largely depends on developments due to inadequate fluid intake relative to fluid losses
(during exercise fluid losses are largely attributable to sweating)
How does hypohydration impair performance when there is 1-2% body mass loss?
Minimal impact
How does hypohydration impair performance when there is 2-3% body mass loss?
May degrade aerobic performance
Deterioration of sport-specific skills
Reduced cognitive function (with heat stress)
Minimal impact on sprint running
Minimal cognitive function impact (without heat stress)
How does hypohydration impair performance when there is >3% body mass loss?
Impaired cognitive function (even in temperate)
How does hypohydration impair performance when there is 3-4% body mass loss?
Minimal impact on muscle strength and power
Is dehydration a blinding issue?
No
What are potential mechanisms that may impair aerobic performance in warm-hot conditions?
Cardiovascular
Central Nervous system
Peripheral muscular factors
Respiration
Breathing sensations
Thermal comfort/ perceived exertion
Psychological
Temperature/Metabolic/Afferent feedback
Brain metabolism/ Brain Temperature
Blood pressure/Blood flow/ oxygen delivery/ metabolite removal
What is hypohydration?
Negative fluid balance
What is hyperhydration?
Positive fluid balance
What is dynamic dehydration?
Changes over time
How is dehydration measured?
Reference change value (RCV) and dehydration likelihood scale
What is the dehydration threshold?
29 degree (every 1 degree warmer it further declines by 1.6%)
What is the primary mechanism influencing hydration?
Cardiovascular strain (likely a critical primary factor)
What is hydration?
The body’s ability to absorb water, the vital liquid it needs, and is based on how much is available to it.
When is net body water balance challenged?
During period of high sweat rates
How much heat is produced for every L of oxygen consumed, and how much of this heat is used to perform mechanical work?
4kcal of heat is produced for every L of O2
Only about 1kcal used to perform mechanical work
Why is urine colour not always the most effective way of assessing hydration status?
Because it can be affected by different elements of the diet/medicine
Why are cool drinks used during exercise?
Get very quickly into the stomach and cool the body
What does the extent of change in Plasma Osmolality indicate?
5mmol/Kg= 80%
7mmol/Kg= 90%
9mmol/Kg= 95%
13mmol/Kg= 99%
What does the extent of change in Body mass indicate?
1.3%= 80%
2.0%= 90%
2.5%= 95%
3.5%= 99%
What does the extent of change in Urine Sensitive Gravity indicate?
0.005= 80%
0.008= 90%
0.010= 95%
0.014= 99%
