Hydration Flashcards
(24 cards)
Adult body water content
50-60% body mass
lean body tissue = ~75% water
fat mass = ~5-10%
Functions water
temp regulation
nutrient transport (blood/plasma)
protection (tears to protect eyes)
biochemical reactions (end product metabolism/hydrolysis)
medium for reactions
Euhydration
fluid water balance
fluid loss = fluid gain
Dehydration
body water deficit greater than normal daily fluctuation
negative fluid water balance
due to inadequate fluid intake relative to fluid losses (sweat)
Net body water balance
difference between fluid water gain (intake + production) and fluid loss
maintained on day to day basis
challenged during periods of high sweat rates
During exercise sweat rates
environ - hot/humid = increase temp = sweat
muscle contract = create heat = sweat
lose water
Assessment tools to determine hydration status
plasma osmolality
body mass change
urine specific gravity
urine density relative to water
euhydrated at 1.003-1.035
> 2% acute body mass reduction
exercise-associated dehydration
90% chance body water deficits sufficient to be classed as dehydration
Osmolality
measure of the total dissolved particle conc
ions
275-295 mOsm/kg
Why do we sweat?
body’s principal means of preventing excessive body temp during exercise
heat production during exercise
L O2 = 4kcal heat produced
pass to body core
hypothalamus sense increase in body temp
increase blood flow to skin = initiate sweat response
Evaporative cooling
1L sweat evaportated = remove 573kcal heat from body
Sweat
water loss from water component of blood (plasma) = reduced plasma and blood volume
sweat hypotonic = plasma osmolality reduces
lower blood volume = increase vascular strain due to heart working harder
Mechanism control body temp
sweating
evaporative heat loss
Dehydration on aerobic performance
29 degree celcius threshold
increase temp (1 degree) = performance decrease (1.6%)
blinded dehydration impair endurance performance
Mechanisms of impaired aerobic performance in warm-hot conditions
Cardiovascular – blood pressure and blood flow, oxygen delivery, metabolite removal
Central nervous system – brain metabolism, brain temperature
Peripheral muscular factors – temperature, metabolic, afferent feedback
Psychological – thermal comfort, perceived exertion
Respiration – breathing sensations
Pre exercise
2-4h = 5-10ml fluid/kg body weight
more fluid if no/dark urine
fluid retention add sodium/salt
During exercise
limit body mass change through loss of fluid to <2%
limit excessive electrolyte imbalance (risk of hyponatremia)
0.4-0.8 L/h
>2h - add sodium (salty sweaters)
>1h - add CHO
Post-exercise
rapid recovery (<12h) = 1.25-1.5L kg/BM loss
+ sodium
more recovery time: resume dietary practices + extra plain water
restoration of sodium and fluid balance
Sweat rate calculation
L/h
weight before - after = weight loss
bottle weight before - after = volume consumed
weight loss + volume consumed - urine loss / duration of exercise (h)
Sodium during exercise
critical for electrolyte balance for functions in body
CHO-E solution
supply CHO as major energy source
effective in maintain hydration status
80-350 kcal/L
sodium = 20-50 mmol/L
Hyponatremia
low blood sodium (<135 mmol/L)
arise from over drinking fluids more than fluid lossses (high sweat sodium losses + low sodium beverages)
recreational athletes/women at risk
dangerous, immediate medical attention
Hyponatremia sytmptoms
changes in personality (confusion or short temper)
fatigue
convulsions or seizures
feeling weak
loss or consciousness/coma
low BP
nauseous/vomiting
Sodium post exercise
dilute conc = consume 50% not reach normal level
ongoing urine release = net balance remain neg
high conc = 125% (reach break even levels)
closer to body water balance in short time
more sodium helps with retention/reabsorption in kidney
