Hydration and exercise Flashcards
How much of a human’s total body mass does water make up?
~60%
What are the fluid compartments of the body and typical volumes?
> Extracellular fluid (14 L)
- plasma (3 L)
- interstitial fluid (11 L)
> Intercellular fluid (28 L)
Describe INTRAcellular dehydration
- 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
What are the physiological responses to INTRAcellular dehydration?
> AVP released, causing renal water retention and increased urine conc
thirst
Describe EXTRAcellular dehydration
- 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
What are the physiological responses to EXTRAcellular dehydration?
> renal water retention
renal sodium retention
peripheral and renal vasoconstriction
thirst
What is the most common (best) haematological method of assessing intracellular hydration?
plasma osmolality
What range of plasma osmolality is indicative of euhydration?
280 -290 mOsmol/kg
What increase in plasma osmolality is associated with a reduction in body mass of 1-2%?
5-7 mOsmol/kg
- (Popowski et al, 2001)
Is plasma osmolality fast or slow responding to fluid loss and recovery upon fluid intake?
fast
What is an issue with using plasma osmolality to assess whole body hydration?
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)
What are two urinary methods of assessing intracellular dehydration?
> urine osmolality
> urine specific gravity
Are urinary methods of assessing intracellular hydration fast or slow responding to fluid loss and recovery upon fluid intake?
slow
- (Popowskwi et al, 2001)
What is the effect of dehydration on solute concentration in the urine?
increased conc
What urine osmolality values are indicative of euhydration and ~2% dehydration?
euhydration = <700 mOsmol/kg
~2% dehydration = >900 mOsmol/kg
- (Casa, 2005)
What urine specific gravity value would indicate euhydration?
<1.020 g/mL
Are uniary indices’ valid and reliable?
you bet ya
What are the effects of dehydration on…
a) Stroke volume
b) Heart rate
c) RPE
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)
Describe how adding heat stress to dehydration is bad
creates competition between the central (continued function) and peripheral (managing heat loss) circulation for limited blood volume.
How is warmer skin associated with body temperature regulation?
warmer skin = higher blood flow
maximises sweat loss
How common is pre-exercise dehydration?
~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)
Does dehydration affect performance in an endurance capacity, and if so, in what conditions?
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)
Does dehydration affect strength and power performance?
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)
How may dehydration benefit performance?
where the body mass has to be moved against gravity the lower body mass may counteract the effect of dehydration
- (Maughan & Shirreffs, 2010)
Have studies found dehydration being beneficial to speed and power outputs?
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.
How much of a crutch is dehydration to endurance performance?
low fluid ingestion during a time to exhaustion at 88% VO2 max test resulted in impairements to time by 30%
- (Ebert et al, 2007)
What comes under the term cognition?
all mental processes allowing humans to perceive, think and remember, but also to feel emotions and exert control over their environment
What did early studies find in terms of dehydration’s effects on cognitive function?
Soldiers dehydrated through exercise in extreme heat.
significant impairments to cognitive function (speed and accuracy) were observed at 2% dehydration.
- (Gopinathan et al, 1988)
What is the consensus of modern research into dehydration’s effect on cognition?
recent studies have found more modest findings or have found no support of cognitive impairment due to dehydration.
- (Masento et al, 2014)
How is mood state impacted by dehydration?
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)
Through what mechanism is mood and cognitive function impaired when dehydrated?
> 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)
