Water balance Lecture 15

Question 1

What quantity does water make up of a male, female and baby

Answer 1

Male = 60% 42L
Female = 50% (more fat) 30L
Baby = 75%

Question 2

How is fluid lost in the body and at what values?

Answer 2

Sweat/skin = 600mL
Urine = 1300mL
Respiration = 200mL
Feces = 100mL

Total = 2200mL

Question 3

How is fluid gained within the body?

Answer 3

Drink = 1200mL
Food = 700mL
Metabolic = 300 mL

Total = 2200mL

Question 4

How are water volumes maintained within the body?

Answer 4

Blood/plasma osmolarity and volume are monitored by the hypothalamus and other centers… regulates blood pressure and omsolarity around 290mOsmol/L

Renal function = excretion

Question 5

What stimulates loss of water by the kidney?

Answer 5

Low plasma osmolarity

Question 6

What does an increase in plasma omsolality do?

Answer 6

Stimulates thirst and decreases urine output

Question 7

Does absence of thirst mean osmolarity has been restored?

Answer 7

No, other mechanisms such as stomach distension can decrease thirst.

Question 8

How does water play a role in temperature regulation?

Answer 8

Sweat is the primary mechanism against hyperthermia

Question 9

How is heat lost from the body?

Answer 9

Convection
Conduction
Radiation (mostly-60%)
Evapouration

Question 10

During exercise what heat loss mechanism is primary?

Answer 10

Evaporation accounts for 80% heat loss

Question 11

How much heat absorption does sweat do?

Answer 11

1L of sweat can remove 2400kJ of heat

Question 12

What does secretion of sweat represent?

Answer 12

A loss of water and Salt from all compartments of the body

Question 13

Does dehydration impair performance?

Answer 13

Yes, as little as 2% body weight loss in water can impair performance

i.e 70kg male 2%= 1.4kg water loss

Question 14

Is everyone affected by water loss in the same way?

Answer 14

No it affects some people more than others.

Question 15

How does changing degrees of water loss affect performance?

Answer 15

As the water loss gets beyond 2% body mass, the decrease in performance (slope) greatly increases. i.e 5% body mass loss in water decreases optimal performance by 30%

Question 16

What are some physiological affects of dehydration?

Answer 16

Reduced blood volume
- Lower CO
- Increased viscosity
Decreased skin blood flow
= Decreased sweating rate
= Decreased heat dissipation
- Increased Core temperature
- Increased use of muscle glycogen as reduced flow to liver reduces its release

Question 17

How is dehydration quantified?

Answer 17

Get the subject to void their bladder and then weight them pre exercise. Weight them post exercise after urinating and dry.

Clothes off at all times

Weight change = fluid loss, which can be computed into % Body Mass

Question 18

What are three methods of quantifying dehydration?

Answer 18

Body mass change
Urine Colour
Urine Osmolarity (900mosmolL=Dehydrated) 100-300= adequately hydrated

Question 19

What does fluid intake help with for atheletes?

Answer 19

Fluid intake can help thermoregulatory responses and offset the negative effects of dehydration

Question 20

What fluid should an athlete drink during exercise?

Answer 20

Fluid intake should aim to prevent dehydration of a magnitude equivalent to 2% of body mass.

Question 21

Why is it difficult to consume fluid thats 2% body weight before or during exercise?

Answer 21

Large volume of water can create gastric distress. i.e stomach can hold only 1L water but sweat loss may be 2-3L hr

Difficult to determine sweat rates to compensate
Sometimes not thirsty till 2% body weight has been lost
May not be convenient to drink

Question 22

When athletes voluntarily drink during exercise on average how much of their fluid loss do they replace?

Answer 22

50%

Question 23

What else apart from fluid is lost in sweat?

Answer 23

electrolytes, - although only in a small amount as sweat is hypotonic,.

Electrolyte loss is normally compensated for in the diet.

Question 24

When else is added to sports drinks apart from water and why?

Answer 24

Electrolytes

• Increases palatibility
• Maintains thirst drive
• Increases rates of absorption
• Increases retention of fluid

Question 25

What can too much water intake lead to?

Answer 25

Hyponatremia

If exercising and losing salts then its called exercise associated hyponatremia

Question 26

What is a fluid replacement strategy?

Answer 26

Preevent take 500mL drink
During the event every 15-20min take 150mL drink
Post exercise consume 150% of fluid loss, the extra 50% is for urine losses.

Question 27

What does the ideal sports drink contain?

Answer 27

20-40mmol Na
5-6% CHO
Flavored and cold

Question 28

If fluid retention strategies were to be personalized, what would be taken into account?

Answer 28

• Environmental conditions
• Exercise intensity
• Drinking opportunities
  Field sports, Endurance events
• Beverage composition