Lecture 5: Hydration Flashcards
What is euhydration?
refers to a normal state of body water, with deviations from this norm producing compensatory responses
What is hyperhydration?
A sustained increase in body water, although often transient
What is hypohydration?
refers to a sustained decrease in body water
What is dehydration?
refers to the process of losing water, rather than a state of low body water
What percent of an adult athletes body mass is water?
Roughly 60-70%
How is body water controlled?
Through thirst and kidney regulation of urine output
What is the daily variation of body water content?
less than 1% of body mass
How is water lost in the body?
- Faecal
- Respiratory
- Urine
- Sweat
What are water gains?
- Metabolic Water production
- Food
- Drink
What are the three ways urine is measure pre-exercise?
Urine osmolality, urine specific gravity and urine colour
What is urine osmolarity?
How concentrated your urine is
What are the disadvantages of measuring urine osmolality?
Expensive, accuracy needs first void sample
What urine osmolality shows that you are euhydrated?
<700 mOsmol/kg
What is urine specific gravity?
Compares the density of urine with the density of water
What urine specific gravity means you are euhydrated?
<1.020 mg/cm3
What are the disadvantages of urine specific gravity?
Accuracy needs first void sample
What are the advantages of urine specific gravity?
Relatively cheap and quick results
How do you use urine colour as a measure?
Look at the colour and compare on a scale
What urine colour shows you are euhydrated?
<3 on scale
What are the advantages of measuring urine colour?
Very cheap and quick results, good education tool
What are the disadvantages of measuring urine colour?
Accuracy needs first void sample, affected by other dietary components
What is serum osmolarity?
how concentrated your blood is
What serum osmolarity shows you are euhydrated?
~285 mOsmol/kg
What are the advantages of serum osmolality?
Accuracy is the gold standard
What are the disadvantages of serum osmolality?
Expensive
Does starting exercise hypohydrated help performance?
There is an association, not remarkably strong but starting exercise well hydrated is very important
What state of hydration should you start exercise in?
in a euhydrated state
What are the guidelines for hydration prior to exercise?
Slowly drink 5-7ml/kg at least 4 hours prior to exercise
If urine still dark drink further 3-5ml/kg 2 hours prior
What assists with fluid retention?
Sodium
What is important about beverages in the heat?
Beverage temperature, we want to reduce core temperature as core temperature causes fatigue
What are the effects of dehydration on exercise?
- Decrease in skill performance
- Decrease in mental performance
- Opening of the blood brain barrier
- Increased perception of effort
How does dehydration impair performance?
- Increased body temperature
- Increased RPE
- Decreased mood
How do we measure dehydration?
= (body mass loss/initial body mass) * 100
How to measure sweat loss in L?
= Body mass loss (kg) + fluid intake (L)
How to measure sweat loss in L/h ?
= [ Body mass loss (kg) + fluid intake (L) / time (mins) ] x 60
What is elite athletes perception of fluid balance compared to their actual fluid balance?
They lost a lot more than they thought, they though they would maintain/gain
- they actually lost weight
How are hydration stratagies traditionally promoted?
centered on the recognition of individual sweat rates
How much do athletes and adults underestimate their sweat losses by?
around 40-50%
What are the effects of overhydration?
- Increase in body mass
- Urination
- Dilution of blood sodium
- Hyponatremia?
What is Hyponatremia?
occurs when the concentration of sodium in your blood is abnormally low
What serum concentration indicates hyponatremia?
[Na] <135 mmol/L
What are the symptoms of hyponatremia?
- Fatigue
- Lethargy
- Brain aneurisms
- Death
What is the issue with the symptoms of hyponatremia?
Symptoms are similar to dehydration, therefore a lot of people were treated with MORE water, making the situation even worse.
What is the incidence of hyponatremia in endurance events?
10-40%
What type of exercise is a risk factor for hyponatermia?
Longer than 4h, slower speeds (more chance to drink), extremely hot or humid enviornments
What personal characteristics are risk factors for hyponatermia?
Females, low body weight (lower total body water to start with)
What medication is a risk factor for hyponatremia?
Non-steroidal anti-inflammatories (generally for pain)
What is the biggest risk factor for hyponatremia?
Excessive fluid intakes
What cannot prevent the development of exercise-associated hyponatraemia?
The addition of sodium to drinks ingested
What are the ACSM drink guidlines?
- Try to limit dehydration to <1-2% loss in body mass
- Avoid gaining weight
What is the major electrolyte lost in sweat?
Sodium (20-80mmol/L)
What are sweat potassium concentrations?
approx. 2-8mmol/L
How do you calculate salt losses?
Sweat sodium concentration (mmol/L) x sweat loss (L/h)
How to convert sweat sodium (mmol) to milligrams?
x 22.99
Why is sodium included in sports drinks?
- Improves palatability
- Maintains extracellular volume
- May attenuate the decline in blood sodium
How does sodium affect thirst?
Sodium ingestion may promote fluid intake via increasing thirst and delay dehydration
How does sodium affect gastric emptying/intestinal absorption?
Sodium is important for intestinal absorption - however the inclusion of sodium in a drink does not effect gastric emptying of intestinal absorption
What are the guidelines for dehydration recovery?
Smaller regular volumes best
What does rehydration within 6 hours require?
volumes greater than deficits induced i.e., 1.5 * BM losses
What are the aims of recovery after exercise?
- Restore Muscle and liver glycogen levels to pre-ex.
- Rehydrate to restore fluid and electrolyte balance * 1.5* BM loss
- Repair, muscle repair & regeneration
How much water do you need to drink to replace weight lost during exercise?
Need to replace 1.5 times body mass lost to become Euhydrated post exercise
Why do you need to drink more than you lose after exercise?
due to obligatory water losses
What is the ideal ingestion rate of water?
Very unclear - Ingesting a given volume over a longer period of time is likely to result in more efficient rehydration
What is sodium the major ion of?
ECF
Why is salty water better to drink after exercise?
some sodium remains in the vascular space = plasma osmolality and sodium concentrations do not decline as may occur if plain water is ingested
How does CHO affect rehydration?
enhances fluid retention if the concentration of carbohydrate (6-10%) and volume of fluid (150% BM loss) ingested are sufficiently high
How does protein affect rehydration?
related to a slowing of the overall rate of fluid uptake
What concentration of salt in sports drinks was most liked by athletes?
18 and 30mmol/L
