3. hydration Flashcards
importance of hydration (4)
- maintains blood volume and osmolarity
- remove wastes and toxins (filtration in kidneys)
- ensures proper neural conduction for muscle function
- regulates body temp
dehydration is associated with (2)
- result
- compensation
- increased core temp
- decreased blood volume (decreased stroke volume)
- decreased muscular endurance and strength
- HR increases in attempt to compensate
dehydration and % body mass loss
- 1-2%
- decrease temp control
- increase HR
dehydration and % body mass loss
3%
- 10% decrease in muscle performance
* not clinical problem but strong effect
dehydration and % body mass loss
4-6%
- decrease muscle strength and hand eye coordination
dehydration and % body mass loss
+6%
decrease blood volume
increase respiration rate
nausea and confusion
dehydration and % body mass loss
+10%
heat stroke
fainting
exhaustion
purpose of sweating
decrease core body temp
if not rehydrating when sweating
decrease in body fluids
leads to decrease in blood volume
further increases core body temp
volume of fluid that can be lost per hour of exercise
- terms of body mass
1-2 leters
~2-3% body mass/hour (assuming 67kg athlete)
factors that affect dehydration
- environmental
- individual
environment
- hot and humid conditions
- clothing/equipment
- lack of rehydration
individual
- effort
- training level
- sweat rate (genetic)
physiological impact of dehydration (8)
- increased (5) and decreased (3)
increased
- plasma osmolarity
- HR
- skin and core temp
- RPE (rating of perceived exhaustion)
- CHO oxidation (glycogen stores deplete faster)
decreased
- plasma volume
- cardiac filling
- sweat rate and skin blood flow
study results
- hydration status and what athletes voluntarily drink
- running time vs core temperature
60 mins of running
- athletes “voluntarily” drink less than 50% of their body fluid loss during exercise
*water ad libitum (voluntary drinking)
critical temp for experiencing central fatigue
~39C
water ad libitum
voluntary drinking during exercise
- what we choose to drink
study result
- 10 well trained cyclists
- 5k hill climb
- either euhydrated (EUH - normal hydration) or dehydrated (DEH - 1% of body mass)
EUH - faster (5.8%)
DEH - higher core temp, RPE (rating of perceived exhaustion), decreased sweat rate
measuring sweat loss volume
total sweat volume loss
pre-exercise mass) - (post exercise mass) + (fluid intake) + (urine output
goals in preventing dehydration during exercise (4)
- drink fluids at least 80% of sweat volume loss
- aim for 60-90min
- heat increases CHO use
problems with over drinking
hyponatremia
- low blood sodium
benefits of CHO in fluids
- shown to enhance performance in exercise greater than 60-90min
- heat increases CHO use
- CHO used 2-4 times faster with intermittent sprints (stop and go sports)
- enhances recovery
study results
- endurance trained men exercising at 69% VO2max
- 8% carb vs placebo drink
time to exhaustion increased 30%
- plasma glucose remained above resting while placebo initial increase before fast decline
study results
- hockey players on ice scrimmage
- no fluid (NF) vs CHO/electrolyte soln
no fluid
- approx 2% body mass decrease
- slightly higher sweat rate
- higher core temp during
- impaired drill performance
benefits of sport drinks
flavour encourages drinking
contains 2-6% extra energy
- extra energy in muscle and brain
- maintains blood glucose levels
similar absorptive capacity as water
contains electrolytes
- Na, Cl, K
- replace salt loss in sweat
- retain fluid in body and blood
CHO mouth rinsing mechanism
- not swallowing
mental/cognitive stimulation of CNS by oral receptor exposure to CHO with
study results
- CHO mouth rinsing
- 2 performance trials with carb rinse (6.4%) and placebo
- rinse 5sec every few mins
- approximately 1hr of exercise
CHO rinse significantly improved performance
- results highly variable
controversy and question with CHO mouth rinsing
- possible benefits
- studies 1hr and stop/go events)
- duration of rinse
- frequency
- muscle and liver glycogen stores
- duration of fasting before trial
- type of activity
benefits?
- may not like stomach full of fluid
- may alter sensitivity of receptors
*
recommended fluid intake before exercise
- how quickly dehydrated subjects return to hydrated state
600-700mL of water or sport drink approximately 60-90mins prior
- all dehydrated subjects returned to hydrated status in 45mins
- hydration status assessed by measuring urine specific gravity
optimal fluid intake goals ‘after’ training
goal
- replace lost fluid and electrolyte stores
- within 2hrs following
- need to also help body re-synthesize liver and muscle glycogen stores
