Hydration and exercise

Question 1

How much of a human’s total body mass does water make up?

Answer 1

~60%

Question 2

What are the fluid compartments of the body and typical volumes?

Answer 2

> Extracellular fluid (14 L)

• plasma (3 L)
• interstitial fluid (11 L)

> Intercellular fluid (28 L)

Question 3

Describe INTRAcellular dehydration

Answer 3

• fluid loss is hypo-osmotic to plasma
• water loss > osmolyte loss
• increased plasma osmolality
• water loss shared between ICF and ECF due to osmotic gradient
• associated with sweat loss due to exercise heat stress

Question 4

What are the physiological responses to INTRAcellular dehydration?

Answer 4

> AVP released, causing renal water retention and increased urine conc
thirst

Question 5

Describe EXTRAcellular dehydration

Answer 5

• fluid loss is iso-osmotic with plasma
• water loss = osmolyte loss
• regular plasma osmolality, therefore, no osmotic gradient to pull water from large ICF resevoir
• associated with fluid losses induced by diuretics, diarrhoea, cold and altitude

Question 6

What are the physiological responses to EXTRAcellular dehydration?

Answer 6

> renal water retention
renal sodium retention
peripheral and renal vasoconstriction
thirst

Question 7

What is the most common (best) haematological method of assessing intracellular hydration?

Answer 7

plasma osmolality

Question 8

What range of plasma osmolality is indicative of euhydration?

Answer 8

280 -290 mOsmol/kg

Question 9

What increase in plasma osmolality is associated with a reduction in body mass of 1-2%?

Answer 9

5-7 mOsmol/kg

- (Popowski et al, 2001)

Question 10

Is plasma osmolality fast or slow responding to fluid loss and recovery upon fluid intake?

Answer 10

fast

Question 11

What is an issue with using plasma osmolality to assess whole body hydration?

Answer 11

plasma variables not affected by dehydration until a certain level of body water loss, therefore, may not be representative of whole body hydration when fluid compartments are constantly fluctuating.
- (Armstrong et al, 2007)

Question 12

What are two urinary methods of assessing intracellular dehydration?

Answer 12

> urine osmolality

> urine specific gravity

Question 13

Are urinary methods of assessing intracellular hydration fast or slow responding to fluid loss and recovery upon fluid intake?

Answer 13

slow

- (Popowskwi et al, 2001)

Question 14

What is the effect of dehydration on solute concentration in the urine?

Answer 14

increased conc

Question 15

What urine osmolality values are indicative of euhydration and ~2% dehydration?

Answer 15

euhydration = <700 mOsmol/kg
~2% dehydration = >900 mOsmol/kg
- (Casa, 2005)

Question 16

What urine specific gravity value would indicate euhydration?

Answer 16

<1.020 g/mL

Question 17

Are uniary indices’ valid and reliable?

Answer 17

you bet ya

Question 18

What are the effects of dehydration on…

a) Stroke volume
b) Heart rate
c) RPE

Answer 18

a) lowered SV due to fluid loss
b) increased HR to maintain CV
c) increased RPE

greater dehydration and for longer duration makes effects more profound.
- (Montain & Coyle, 1992)

Question 19

Describe how adding heat stress to dehydration is bad

Answer 19

creates competition between the central (continued function) and peripheral (managing heat loss) circulation for limited blood volume.

Question 20

How is warmer skin associated with body temperature regulation?

Answer 20

warmer skin = higher blood flow

maximises sweat loss

Question 21

How common is pre-exercise dehydration?

Answer 21

~2/3 of athletes had urine specific gravity values above euhydrated boundries when spot tested prior to training.
- (Volpe et al, 2009)

37% of usual gym going adults tested with urine osmolality above >900 mOsmol/kg
- (Peacock et al, 2011)

Question 22

Does dehydration affect performance in an endurance capacity, and if so, in what conditions?

Answer 22

Dehydration of >2% body mass loss consistently decreases endurance performance when exercise duration is >90 minutes and in temperatures of >30 degrees.
- (Cheuvront et al, 2003)

Question 23

Does dehydration affect strength and power performance?

Answer 23

Across multiple levels of dehydration (2-7%) the research is not conclusive for strength/power detriments as it is for endurance detriments.
- (Cheuvront & Kenefick, 2014)

Dehydration found not to affect vert jump performance and only had significantly detrimental effects on sets 2 and 3 of 6 in a back squat.
- (Judelson et al, 2017)

Question 24

How may dehydration benefit performance?

Answer 24

where the body mass has to be moved against gravity the lower body mass may counteract the effect of dehydration
- (Maughan & Shirreffs, 2010)

Question 25

Have studies found dehydration being beneficial to speed and power outputs?

Answer 25

no,
Watson et al (2005) tested 6 elite sprinters in 50, 200 and 400m sprints and a vert jump when either 2.5% dehydrated or euhydrated.
There were no significant differences in the results between the two trials.

Question 26

How much of a crutch is dehydration to endurance performance?

Answer 26

low fluid ingestion during a time to exhaustion at 88% VO2 max test resulted in impairements to time by 30%
- (Ebert et al, 2007)

Question 27

What comes under the term cognition?

Answer 27

all mental processes allowing humans to perceive, think and remember, but also to feel emotions and exert control over their environment

Question 28

What did early studies find in terms of dehydration’s effects on cognitive function?

Answer 28

Soldiers dehydrated through exercise in extreme heat.
significant impairments to cognitive function (speed and accuracy) were observed at 2% dehydration.
- (Gopinathan et al, 1988)

Question 29

What is the consensus of modern research into dehydration’s effect on cognition?

Answer 29

recent studies have found more modest findings or have found no support of cognitive impairment due to dehydration.
- (Masento et al, 2014)

Question 30

How is mood state impacted by dehydration?

Answer 30

studies measuring self-reported change in mental state have consistently found associations between dehydration and mood states.
- (Masento et al, 2014)

Reduced reported concentration and increased headaches with fluid restriction over a period of 37 hours
- (Shirreffs et al, 2004)

Question 31

Through what mechanism is mood and cognitive function impaired when dehydrated?

Answer 31

> dehydration increases activation in regions of the brain associated with emotion/behaviour
a shift in neural resources with dehydration means that higher levels of neural activity are required to complete the same task, explaining slower reaction times observed with dehydration.
- (Peacock et al, 2010)