Hydration (Fluid and electrolyte requirements for exercise) Flashcards
Adult body = 50-60% water, how much of this is in lean body tissue, and how much in fat mass?
– Lean body tissues = ~75%water
– Fat mass=~5-10%water
Typically, what is total body-water volume?
42L or 60% of body mass
What is hypohydration?
The uncompensated loss of body water.
What is net body water balance?
The difference between fluid water gain (intake + production) and fluid loss.
Typically, well maintained on a day-to-day basis (within 1% of body mass).
When is net body water balance most challenged?
During periods of high sweat rates.
Define dehydration (hypohydration)
A body water deficit greater than normal daily fluctuation.
What is the most sensitive and simple measure to determine acute changes in body water?
Change in body mass.
Acutely: >2% body mass reduction = 90%
chance that body water deficits are sufficient to be classed as dehydration.
The best static physiological index of hydration status is the measurement of plasma osmolality.
What is osmolarity?
A measure of the total dissolved particle concentration (mOsm/kg)
– Typically 275-295 mOsm/kg
Dynamic dehydration assessment can be tracked well with..?
- Body mass change (in energy balance)
- Plasma osmolarity
- Urine specific gravity
Urine density relative to water (water = 1.00)
Euhydrated at 1.003–1.035 U (Eu)
Dehydration likelihood scale example:
If someone has a 90% probability, what is there dehydration likelihood?
More likely
Explain how heat production during exercise causes us to sweat.
For every L of O2 consumed, 4kcal of heat is produced and only about 1kcal is used to perform mechanical work (most heat is passed to body core).
Hypothalamus senses increase in body (and skin) temp, and responds to increase blood flow to skin and initiate sweating response.
Why do we sweat, and what are normal body temperatures?
Sweating is the body’s principal means of
preventing excessive rises in body temperature during exercise (hyperthermia).
Normal body temperature is 36-38 °C
During exercise is 38-40 °C
How many kcal of heat does 1L of sweat evaporating remove?
573kcal
Sweat is hypotonic as compared to plasma, therefore..?
Plasma osmolarity increases.
What impact does 1-2% BM loss have on performance?
Minimal impact
What impact does 2-3% BM loss have on performance?
May degrade aerobic performance (moreso in heat)
Deterioration of sport-specific skills
Minimal impact on sprint running
Minimal cognitive function impact (without heat stress)
Reduced cognitive function (with heat stress)
What impact does >3% BM loss have on performance?
Impaired cognitive function (even in temperate)
What impact does 3-4% BM loss have on strengthand power performance?
Minimal impact on muscle strength and power
What are the potential CV mechanisms of impaired aerobic performance in warm-hot conditions?
Blood pressure and blood flow, oxygen delivery, metabolite removal
What are the ACSM guidelines for 2-4 h pre-event?
5-10 ml fluid/kg body weight (sodium, salt snacks or small meals may help)
More fluid if no/dark urine
What are the ACSM guidelines for during exercise?
Sufficient fluid to limit body mass losses to <2% and limit excessive electrolyte imbalance (pre-post weighing can
help in estimation)** (typically 0.4 –0.8 L/h [cool, flavour])
➢>2 h (or salty sweaters) –add sodium
➢>1 h –may consider CHO addition
What are the ACSM guidelines for post- exercise?
Rapid recovery(<12 h): Consume1.25-1.5 L for each kg BM loss + sodium
More recovery time: resume dietary practices + extra plain water
What is the use of sodium pre exercise, during exercise, and post exercise?
pre - fluid retention
during - limit electrolyte losses (risk of hyponatremia), stimulate thirst
post - restoration of sodium & fluid balance
other electrolytes, though lost in sweat do not seem critical for hydration.
During exercise, you should intake sufficient fluid to limit body mass losses to <?%.
<2%
What should a CHO-E do?
– Supply CHO as the major energy source
– Be effective in maintaining hydration status
How much energy should a CHO-E provide?
80-350 kcal/L from CHO, ≥75% of
energy from CHOs that induce high
glycaemic response
e.g., glucose, glucose polymers, sucrose
How much sodium should a CHO-E provide?
Sodium: 20-50 mmol/L (460 – 1150 mg/L)
What is hyponatremia?
A condition where sodium levels in the blood are abnormally low.
What classifies ‘low blood sodium’?
<135 mmol/L
How can hyponatremia arise?
From over drinking fluids more than fluid losses (exacerbated with high sweat
sodium losses + low sodium beverages)
Recreational athletes and women at greater risk
