Week 4

Question 1

How much of the adult body, lean body tissues, and fat mass are made up of water?

Answer 1

Adult body = 50-60% water

Lean body tissues (muscle, heart, liver) = approx 75% water

Fat mass = approx 5-10% water

Question 2

What are key functions of water

Answer 2

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

Question 3

Intra and extracelluar fluid in relation to water content

Answer 3

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

Question 4

What is in fluid (water) balance (euhydration)

Answer 4

Fluid gain = fluid loss

Question 5

How do you gain, and hoe do you lose fluid?

Answer 5

Fluid gain – drink, food, metabolic (e.g. breakdown of glycogen). Usually matched with respiration in fluid loss.

Fluid loss – respiration, skin, feces, urine

Question 6

If someone lost 1000ml of fluid through exercise, what would they be in?

And what would kick in to restore euhydration?

Answer 6

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.

Question 7

What is net body water balance

Answer 7

Net body water balance is the difference between fluid water gain (intake and production) and fluid loss.

Question 8

Is net water body balance well maintained on a day to day basis?

What challenges it?

Answer 8

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

Question 9

What is dehydration or hypohydration

Answer 9

> 2% body mass reduction

Body water deficit greater than normal daily fluctuation

Question 10

How would you statically assess hydration status in someone?

Answer 10

Best static physiological index of hydration status is plasma osmolality – a measure of the total dissolved particle concentration in mOsm/kg

Question 11

Plasma osmolality going down is related to dehydration
T or F?

Answer 11

F - Increased Osm means dehydration - any value over 295 mOsm/kg is related to dehydration

(Typical value is 275-295)

Question 12

How can dynamic dehydration be tracked?

Answer 12

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)

Question 13

What is Reference change value

Answer 13

Reference change value (RCV) - change from baseline to after exercise – probability that you will be dehydrated

Question 14

As dehydration liklihood increases, what happens to plasma osmolality, % body mass loss, and urine specific gravity?

Answer 14

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

Question 15

Why do we sweat?

Answer 15

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).

Question 16

Why are hot and humid conditions more challenging than hot and dry

Answer 16

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

Question 17

During periods of high sweat, ad libitum (free choice drinking) will lead to…

Answer 17

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

Question 18

Why does the heart have to work harder in order to get the nutrients in the blood to the muscles

Answer 18

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

Question 19

Does hypohydration impair performance?

Answer 19

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

Question 20

Impact of blinded dehydration on aerobic performance

Answer 20

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.

Question 21

Potential mechanisms of impaired aerobic performance in warm/hot conditions

Answer 21

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

Question 22

Guidelines for fluid consumption 2-4h pre event

Answer 22

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.

Question 23

What does the colour of urine mean?

Answer 23

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.

Question 24

How does sodium help pre exercise?

Answer 24

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.

Question 25

How does pre exercise hyperhydration help

Answer 25

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

Question 26

Guidelines for fluid consumption during exercise

Answer 26

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

Question 27

How are sweat losses variable between individuals?

Answer 27

Therefore can calculate sweat rate – what would fluid intake need to be to onset body mass losses to less than 2%.

Question 28

KNOW HOW TO CALCULATE SWEAT RATE

Answer 28

Sweat rate (L/h) = weight loss + volume consumed - urine loss / duration of exercise

Question 29

What is one assumption we make about sweat loss

Answer 29

1kg body mass loss = 1kg body water loss (assumption)

Question 30

Why is sodium necessary during exercise

Answer 30

Sodium necessary during exercise as limits electrolyte losses (risk of hyponatremia). Also stimulates thirst

Question 31

How much sodium should be consumed

Answer 31

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

Question 32

Hyponatremia
What is it
How does it arise
Who is at most risk

Answer 32

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

Question 33

Guidlines for fluid consumption post exercise

Answer 33

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

Question 34

Why should you ingest sodium post ex?

Answer 34

restoration of sodium and fluid balance