Hydration (Fluid and electrolyte requirements for exercise)

Question 1

Adult body = 50-60% water, how much of this is in lean body tissue, and how much in fat mass?

Answer 1

– Lean body tissues = ~75%water
– Fat mass=~5-10%water

Question 2

Typically, what is total body-water volume?

Answer 2

42L or 60% of body mass

Question 3

What is hypohydration?

Answer 3

The uncompensated loss of body water.

Question 4

What is net body water balance?

Answer 4

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

Typically, well maintained on a day-to-day basis (within 1% of body mass).

Question 5

When is net body water balance most challenged?

Answer 5

During periods of high sweat rates.

Question 6

Define dehydration (hypohydration)

Answer 6

A body water deficit greater than normal daily fluctuation.

Question 7

What is the most sensitive and simple measure to determine acute changes in body water?

Answer 7

Change in body mass.

Acutely: >2% body mass reduction = 90%
chance that body water deficits are sufficient to be classed as dehydration.

Question 8

The best static physiological index of hydration status is the measurement of plasma osmolality.

What is osmolarity?

Answer 8

A measure of the total dissolved particle concentration (mOsm/kg)
– Typically 275-295 mOsm/kg

Question 9

Dynamic dehydration assessment can be tracked well with..?

Answer 9

• Body mass change (in energy balance)
• Plasma osmolarity
• Urine specific gravity
   Urine density relative to water (water = 1.00)
   Euhydrated at 1.003–1.035 U (Eu)

Question 10

Dehydration likelihood scale example:

If someone has a 90% probability, what is there dehydration likelihood?

Answer 10

More likely

Question 11

Explain how heat production during exercise causes us to sweat.

Answer 11

For every L of O2 consumed, 4kcal of heat is produced and only about 1kcal is used to perform mechanical work (most heat is passed to body core).

Hypothalamus senses increase in body (and skin) temp, and responds to increase blood flow to skin and initiate sweating response.

Question 12

Why do we sweat, and what are normal body temperatures?

Answer 12

Sweating is the body’s principal means of
preventing excessive rises in body temperature during exercise (hyperthermia).

Normal body temperature is 36-38 °C
During exercise is 38-40 °C

Question 13

How many kcal of heat does 1L of sweat evaporating remove?

Answer 13

573kcal

Question 14

Sweat is hypotonic as compared to plasma, therefore..?

Answer 14

Plasma osmolarity increases.

Question 15

What impact does 1-2% BM loss have on performance?

Answer 15

Minimal impact

Question 16

What impact does 2-3% BM loss have on performance?

Answer 16

May degrade aerobic performance (moreso in heat)
Deterioration of sport-specific skills
Minimal impact on sprint running
Minimal cognitive function impact (without heat stress)
Reduced cognitive function (with heat stress)

Question 17

What impact does >3% BM loss have on performance?

Answer 17

Impaired cognitive function (even in temperate)

Question 18

What impact does 3-4% BM loss have on strengthand power performance?

Answer 18

Minimal impact on muscle strength and power

Question 19

What are the potential CV mechanisms of impaired aerobic performance in warm-hot conditions?

Answer 19

Blood pressure and blood flow, oxygen delivery, metabolite removal

Question 20

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

Answer 20

5-10 ml fluid/kg body weight (sodium, salt snacks or small meals may help)

More fluid if no/dark urine

Question 21

What are the ACSM guidelines for during exercise?

Answer 21

Sufficient fluid to 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])
➢>2 h (or salty sweaters) –add sodium
➢>1 h –may consider CHO addition

Question 22

What are the ACSM guidelines for post- exercise?

Answer 22

Rapid recovery(<12 h): Consume1.25-1.5 L for each kg BM loss + sodium
More recovery time: resume dietary practices + extra plain water

Question 23

What is the use of sodium pre exercise, during exercise, and post exercise?

Answer 23

pre - fluid retention
during - limit electrolyte losses (risk of hyponatremia), stimulate thirst
post - restoration of sodium & fluid balance

other electrolytes, though lost in sweat do not seem critical for hydration.

Question 24

During exercise, you should intake sufficient fluid to limit body mass losses to <?%.

Answer 24

<2%

Question 25

What should a CHO-E do?

Answer 25

– Supply CHO as the major energy source
– Be effective in maintaining hydration status

Question 26

How much energy should a CHO-E provide?

Answer 26

80-350 kcal/L from CHO, ≥75% of
energy from CHOs that induce high
glycaemic response
e.g., glucose, glucose polymers, sucrose

Question 27

How much sodium should a CHO-E provide?

Answer 27

Sodium: 20-50 mmol/L (460 – 1150 mg/L)

Question 28

What is hyponatremia?

Answer 28

A condition where sodium levels in the blood are abnormally low.

Question 29

What classifies ‘low blood sodium’?

Answer 29

<135 mmol/L

Question 30

How can hyponatremia arise?

Answer 30

From over drinking fluids more than fluid losses (exacerbated with high sweat
sodium losses + low sodium beverages)

Recreational athletes and women at greater risk