Week 4 Flashcards
How much of the adult body, lean body tissues, and fat mass are made up of water?
Adult body = 50-60% water
Lean body tissues (muscle, heart, liver) = approx 75% water
Fat mass = approx 5-10% water
What are key functions of water
Functions: nutrient transport (blood and plasma is water), protection (tears, lubrication, synovial fluid), temperature regulation, biochemical reactions, (hydrolysis is splitting something with water) medium for reactions
Intra and extracelluar fluid in relation to water content
Intracellular fluid – 2/3 of total body water content, but in context of hydration status, the extracelluar fluid is most important
Extracelluar fluid – contains the interstitial fluid (between cells) and blood plasma
What is in fluid (water) balance (euhydration)
Fluid gain = fluid loss
How do you gain, and hoe do you lose fluid?
Fluid gain – drink, food, metabolic (e.g. breakdown of glycogen). Usually matched with respiration in fluid loss.
Fluid loss – respiration, skin, feces, urine
If someone lost 1000ml of fluid through exercise, what would they be in?
And what would kick in to restore euhydration?
Extra 1000ml fluid loss from exercise meaning negative fluid (water) balance (dehydration, hypohydration). If they drunk/ate 1000ml, then they would return to euhydration. Thirst and hunger kick in to regulate fluid balance.
What is net body water balance
Net body water balance is the difference between fluid water gain (intake and production) and fluid loss.
Is net water body balance well maintained on a day to day basis?
What challenges it?
Typically, well maintained on a day to day basis (within 1% body mass) (thirst and hunger drives).
Net body water balance can be challenged during period of high sweat rates
What is dehydration or hypohydration
> 2% body mass reduction
Body water deficit greater than normal daily fluctuation
How would you statically assess hydration status in someone?
Best static physiological index of hydration status is plasma osmolality – a measure of the total dissolved particle concentration in mOsm/kg
Plasma osmolality going down is related to dehydration
T or F?
F - Increased Osm means dehydration - any value over 295 mOsm/kg is related to dehydration
(Typical value is 275-295)
How can dynamic dehydration be tracked?
Body mass change – through sweating
Plasma osmolality
Urine specific gravity – urine density relative to water – water = 1.00. euhydrated at 1.003-1.035 (Eu)
What is Reference change value
Reference change value (RCV) - change from baseline to after exercise – probability that you will be dehydrated
As dehydration liklihood increases, what happens to plasma osmolality, % body mass loss, and urine specific gravity?
Plasma osmolality increases with dehydration probability
Urine specific gravity also increases
% body mass loss also increases. 2% body mass loss relates to 90% chance you are dehydrated
Why do we sweat?
For every L of oxygen consumed 4kcal of heat is produced and only about 1kcal is used to perform mechanical work (most is wasted on heat production)
Most of this heat is passed to body core via bloodstream
Hypothalamus senses increase in body and skin temperature
Responds to increase blood flow to skin and initiate sweating to dissipate heat through sweat. Preventing excessive rises in temp (hyperthermia).
Why are hot and humid conditions more challenging than hot and dry
Sweating is the bodys main mean of preventing exercise rises in body temperature during exercise (hyperthermia)
Evaporation of sweat on skin cools the body
Hot and dry – sweating is possible – water content is low, meaning evaporation is possible
Hot and humid – water content is high, meaning evaporation is hard meaning sweat drips off skin onto floor, which wont help keep body cool
During periods of high sweat, ad libitum (free choice drinking) will lead to…
During periods of high sweat, ad libitum (free choice drinking) will lead to body mass loss
Due to ad libitum being insufficient to replace lost water
Why does the heart have to work harder in order to get the nutrients in the blood to the muscles
Water loss from the water component of the blood (plasma) = reduce plasma and blood volume. Water component of the sweat comes from the plasma meaning reduce plasma volume, and blood volume. This means heart has to work harder to get the nutrients in the blood to the muscles.
Therefore, lower blood volume increases the cardiovascular strain of the exercise. Exercise in a dehydrated state means HR higher (less blood available meaning heart has to work harder).
Sweat is hypotonic as compared to plasma, therefore plasma osmolality increases
Does hypohydration impair performance?
1-2% BM loss – minimal impact
2-3% - May degrade aerobic performance– minimal impact on sprint running – reduced cognitive function – deterioration of sport specific skills
> 3% - impaired cognitive function
3-4% - minimal impact on muscle strength and power
Impact of blinded dehydration on aerobic performance
Hard to do a blinding study on dehydration – you would know whether you are drinking fluids or not and the whether you should perform better or not
Study done by James et al – used an infusion tube to put fluids into the stomach to maintain hydration status (euhydration condition) and didn’t infuse anything in dehydration condition – blinded dehydration, therefore did worse in time trial.
Potential mechanisms of impaired aerobic performance in warm/hot conditions
Cardiovascular – blood pressure and blood flow, o2 delivery
-reduction in blood voulume puts more pressure on CV system – heart has to work harder to oxyegnate body. Also less blood that goes to the skin to help with thermoregulation. This (cardiovascular strain (high skin blood flow + reduced blood volume)) is likley the critical primary factor
CNS – brain metabolism, brain temp
Periipheral muscular factors – temp, afferent feedback
Psychological – thermal comfort – feels hot – percieved exertion is harder
Respiration – breathing sensations – breathing harder – feels harder
Guidelines for fluid consumption 2-4h pre event
5-10ml fluid/kg body weight (sodium, salt snacks or small meals may help
More fluid if no dark/urine
Pre event – if person weighs 55kg, 5ml/kg = 275ml, 10ml/kg = 550ml. Smaller person may need less in this range.
What does the colour of urine mean?
Darker urine = more dehydrated you (probably) are. However, urine can be affected by diet or supplements. Could think you are dehydrated but you are just taking something to make your urine darker.
Goal is to arrive at exercise at a euhydrated state – water balance.
How does sodium help pre exercise?
Sodium used pre exercise can help with fluid retention – not a bad thing as means keeping it in body – dilutes blood, reducing plasma osmolality. Also helps with reabsorption of water in the kidney, less likely to pass water out as urine.
How does pre exercise hyperhydration help
Pre-exercise hyperhydration (an increase in total body water above that of normal levels) provides a strategy to delay or reduce the adverse effects of exercise-induced hypohydration
Guidelines for fluid consumption during exercise
Sufficient fluid ti limit body mass losses to <2% and limit excessive electrolyte imbalance (pre-post weighing can help in estimation) (typically 0.4-0.8 L/h - cool,flavour)
>2h (or salty sweaters) - add sodium
>1h - may consider CHO addition
Cooler drink particularly in heat helps with thermoregulation. Get quickly into stomach, cooling body.
Flavour can help, encourages voluntary consumption.
=doesn’t necessarily help with hydration but indirectly benefits body and therefore performance
Ex longer for 2h, (or people who are salty sweaters) sodium should be added to beverage or ingested through food like bars or gels with sodium in
Ex for longer than 1h, may consider CHO addition
How are sweat losses variable between individuals?
Therefore can calculate sweat rate – what would fluid intake need to be to onset body mass losses to less than 2%.
KNOW HOW TO CALCULATE SWEAT RATE
Sweat rate (L/h) = weight loss + volume consumed - urine loss / duration of exercise
What is one assumption we make about sweat loss
1kg body mass loss = 1kg body water loss (assumption)
Why is sodium necessary during exercise
Sodium necessary during exercise as limits electrolyte losses (risk of hyponatremia). Also stimulates thirst
How much sodium should be consumed
460-1150 mg/L
Lucozade body fuel has 50mg/100ml sodium (500mg/L) - delivers effective amount of sodium based on above guideline
Fit water has 21mg/100ml - dosent fit guideline – look at ingredients to make sure sodium content is necessary
Hyponatremia
What is it
How does it arise
Who is at most risk
How much sodium in blood stream – low blood sodium - <135mmol/L - risk of hyponatreamia is high.
Hyponatremia is too much water – diluting blood too much
Can arise from over drinking fluids more than fluid losses (exacerbated with high sweat sodium losses + low sodium beverages)
Recreational athletes (running marathons slowly, meaning not sweating, and drinking lots are at risk) and women at greatest risk
Is dangerous, and requires immediate and accurate medical attention
Guidlines for fluid consumption post exercise
Rapid recovery (<12h): cpnsume 1.25-1.5L for each kg BM loss and sodium
More recovery time: resume dietary practices and extra plain water
Why should you ingest sodium post ex?
restoration of sodium and fluid balance
