Week 4 - Hydration

Question 1

What is the % of water in…
a) the adult body
b) lean body tissue
c) fat mass

Answer 1

a) 50-60%
b) 75%
c) 5-10%

Question 2

What are the functions of water?

Answer 2

• Nutrient transport
• Protection
• Temperature regulation
• Biomechanical reactions
• Medium for reactions

Question 3

Where is most of the total body water stored?

Answer 3

Intracellular fluid (62.5% of total body water) and extracellular fluid (37.5% of total body water - interstitial fluid and blood plasma)

Question 4

Examples of fluid loss

Answer 4

• Exercise
• Respiration
• Skin
• Feces
• Urine

Question 5

Examples of fluid gain

Answer 5

• Drink
• Food
• Metabolic

Question 6

Euhydration

Answer 6

in fluid/water balance

Question 7

Net body water balance

Answer 7

the difference between fluid water gain (intake + production) and fluid loss

Question 8

Define dehydration (hypohydration) and how this can be indicated.

Answer 8

Dehydration is defined as a body water deficit greater than normal daily fluctuation. This can be indicated by a body mass loss >2%.

Question 9

How can exercise-associated dehydration be defined?

Answer 9

This can be defined/indicated as an acute body mass loss of >2%.

Question 10

What is the best static physiological index of hydration status?

Answer 10

the measurement of plasma osmolality (a measure of the total dissolved particle concentration)
- Typically 275-395 mOsm/kg
- Increase in this suggests dehydration.

Question 11

Examples of dynamic assessments of hydration status before and after an exercise bout.

Answer 11

• 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)

Question 12

How is the sweating response initiated during exercise in hot temperatures?

Answer 12

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.

Question 13

For every L of oxygen consumed during exercise how many Kcal of heat is produced and where does this heat pass to?

Answer 13

4kcal and it passes to the body core

Question 14

What is evaporative cooling? For every 1L of sweat evaporated, how many kcal of heat is removed from the body?

Answer 14

Evaporative cooling is where we remove heat from the body via sweat evaporation.

573kcal of heat from the body

Question 15

Explain how water loss influences plasma and blood volume?

Answer 15

reduces plasma and blood volume because water loss is from the water component of blood (plasma).

Question 16

How does sweat influence plasma osmolality?

Answer 16

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.

Question 17

How may hypohydration impair performance when we have a BM loss of >2%?

Answer 17

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.

Question 18

What is the main mechanism by which hypohydration affects aerobic performance in warm/hot conditions?

Answer 18

Cardiovascular strain
- High skin blood flow
- Reduced blood volume
- Reduced oxygen delivery
- Reduced metabolite removal

Question 19

What are the ACSM guidelines for hydration 2-4h pre-event?

Answer 19

5-10ml fluid/kg body weight
- Sodium, salt snacks or small meals may help
- More fluid if no/dark urine

Question 20

Why is sodium beneficial…
a) pre-exercise
b) during exercise
c) post-exercise

Answer 20

a) Fluid retention
b) Limit electrolyte losses (risk of hyponatremia) and stimulate thirst
c) restoration of sodium and fluid balance

Question 21

Why may adding sodium to a drink help with fluid retention?

Answer 21

it helps to maintain osmolality and reabsorption of water from kidney

Question 22

What are the ACSM guidelines during exercise?

Answer 22

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

Question 23

What are the ACSM guidelines post-exercise (rapid recovery and more recovery time)?

Answer 23

Rapid recovery (<12h) - consume 1.25-1.5L for each kg BM loss + sodium.
More recovery time - resume dietary practices + extra plain water.

Question 24

How do you calculate sweat rate (liters per hour)?

Answer 24

Weight loss + volume consumed - urine loss / duration of exercise (hrs)

Weight loss = weight before - weight after
Volume consumed = bottle weight before - after

Question 25

What should CHO-E (carbohydrate-electrolyte) solutions do?

Answer 25

• 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)

Question 26

Hyponatremia
- What is it?
- What can it arise from?
- Who are at a greater risk?

Answer 26

• 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.

Question 27

How can we exacerbate hyponatremia?

Answer 27

exacerbated with high sweat
sodium losses + low sodium
beverages

Question 28

What assessment tools can be used to determine hydration status in the 2-4hrs before an athlete starts exercise?

Answer 28

plasma osmolality and urine colour

Question 29

Describe how you could develop an individualised plan for fluid consumption during exercise to minimise the risk of dehydration in an athlete.

Answer 29

Estimate sweat loss from pre-to-post exercise body mass change. Corrected for fluid consumed during exercise and urine produced.