Week 4 - Hydration Flashcards
Describe the percentage of water in an adult body and its distribution in lean body tissues versus fat mass
Adult body is composed of 50-60% water, with lean body tissues containing 75% water and fat mass containing 5-10% water
Define dehydration or hypohydration
Dehydration or hypohydration refers to a body water deficit greater than normal daily fluctuation
Define net body water balance
Net body water balance is the difference between fluid water gain and fluid loss. It can be challenged during periods of high sweat rates
Describe the different assessments for determining dynamic hydration status before and after exercise
Plasma Osmolality (275-295 mOsm/kg)
Body Mass Change
Urine specific gravity (1.003-1.035)
What is the signifiance of a change in body mass in determining dehydration
A change in body mass provides a sensitive and simple measure to determine acute changes in body water, with >2% body mass reduction indicating a 90% chance of dehydration
Describe the role of sweating during exercise
Sweating is the body’s principal means of preventing hyperthermia during exercise by evaporative cooling, removing heat from the body
How does hypohydration impact performance during exercise
1-2%: Minimal imapct
2-3%: May degrade aerobic performance
>3% : Impaired cognitive function
3-4%: Minimal impact on muscle strength and power
Potential Mechanisms of Impaired Aerobic Performance
Cardiovascular (high skin blood flow + reduced blood volume primary factor)
Central nervous system
Peripheral muscular factors
Psychological
Respiration
What are the ACSM guidelines regarding hydration
2-4h pre-event: 5-10ml fluid/kg body weight (sodium or salt snacks may help)
During exercise: Sufficient fluid to limit body mass losses to <2% (0.4-0.8L/h) add sodium + CHO
Post-exercise (<12h): Rapid recovery (1.25-1.5L for each kg BM loss + sodium)
How can hyponatremia occur during exercise
Hyponatremia, low blood sodium levels, can arise from overdrinking fluids more than fluid losses, especially common among recreational athletes and women
What is CHO-E Solution
CHO-E solution is the combination of carbohydrate and sodium in maintaining hydration status.
CHO is >75% of energy that induces high glycaemic response, and 20-50 mmol/L of sodium
Importance of Sodium for hydration
Pre-exercise: fluid retention
During exercise: limit electrolyte losses & stimulate thirst
Post exercise: restoration of sodium & fluid balance
Calculating Sweat Rate
Weight before - weight after = weight loss
Bottle weight before - after = volume consumed
Sweat Rate = (weight loss + volume consumed - urine loss) / duration of exercise (hours)
How much heat is produced during exercise
For every 1L of oxygen consumed, 4kcal of heat is produced, only 1kcal is used to perform mechanical work
How effective is evaporative cooling
1L sweat evaporated will remove 573 kcal of heat from the body
What impact does dehydration have on aerobic perfomance
29C threshold, every 1C increase reduced performance by a further 1.6%
Blinded dehydration impairs endurance performance
What assessment tools can be used to determine hydration status 2-4 hours before exercise
Plasma osmolality
Urine colour
Describe how you could develop an individualised plan for fluid consumption during exercise to minimise the risk of developing dehydration in an athlete
Sweat loss estimated from pre to post-exercise body mass change, corrected for fluid consumed during exercise, and urine produced
How can the environment affect sweat rate losses
Hot & humid conditions can increase sweat rates much more than cold & dry conditions
Not uncommon for sweat rates to exceed 1L/h
