Week 4 - Hydration Flashcards
How much does water make up of the body?
Adult body = 50-60%
Lean body masses - 75%
Fat mass - 5-10%
What are the functions of hydration?
Nutrient Transport
Protection
Temperature Regulation
Biomechanical Reactions
Medium for Reactions
What is the total body water volume?
42L of 60% of body mass
How does sweat rates change at differing running intensities
As pace and heat stress conditions increase so does sweat rate
What is it known as when there is a negative water balance
Dehydration or hypohydration
What is net body water balance
The difference between total water intake and total water loss
What is dehydration
when body water volume is at a greater deficit than normal fluctuation
How can body mass changes indicate water balance changes?
Change in body mass indicates helps determine changes in body water. >2% body mass reduction = 90%
chance that body water deficits are sufficient
to be classed as dehydration
Why do we sweat
Response to an increase in body temperature in an attempt to cool down the body. Its done by the hypothalamus detecting increase in body temp this then results in increase blood flow to skin and initiates the sweating response
What is evaporative cooling
sweat evaporates from your skin, and as it does, it takes heat away with it, cooling you down. 1L sweat evaporated wil remove 573kcal from the body
During periods of high sweat rates drinking will often lead to body water deficit
Sweat loss
water loss from water component of blood (plasma) = decreased plasma volume and blood volume
Sweat is hypotonic compared to plasma, therefore plasma osmolality increases
What leads to dehydration?
Largely due to inadeuqate fluid intake relative to fluid losses, and during exercise fluid losses are largely attributable to sweating
What are the main mechanisms to control body temp?
Sweating and evaporative heat loss to help prevent the development of hyperthermia
How does hypohydration impair exercise?
1-2% minimal impact
2-3% may degrade aerobic performance, deteriation of sport specific skills, minimal impact on sprint running and cognitive function (without heat stress) and reduced cognitive function (with heat stress)
>3% impaired cognitive function
3-4% Minimal impact on muscle strenght and power
How does dehydration impact aerobic performance?
Once body temperature exceeds 29 degrees, each degree warmer performance decreases 1.6%
Impact of blinded dehydration on sport performance
Blinded dehydration impairs aerobic performance, similar performance decline with blinded and unblinded performance
Potential mechanism of impaired aerobic performance in warm conditions
Cardiovascular - blood flow and pressure, oxygen delivery and metabolite removal
Central nervous system - brain metabolism, brain temperature
Peripheral muscular factors - temperature, metabolic, afferent feedback
Psychological - thermal comfort, perceived exertion
Respiration - breathing sensations
Whats the most prominent mechansim by which hypohydrations impacts performance
Cardiovascular strain appears to play the greatest role
Environement also plays a large role in the impact of hypohydration
What are the effects of sodium ingestion pre, during and post exercise?
Pre - Fluid retention
During - Limit electrolyte losses (risk of hyponatremia) stimulate thirst
Post - restoration of sodium and fluid balance
How are carbohydrate - electrolyte solutions characterised
a CHO-E should:
Supply CHO as main energy source
Be effective in maintaining hydration status
What is hyponatremia?
Low blood sodium (<135mmol/L)
Can arise from overdrinking fluids more than fluid losses
(Can be exacerbated by high sweating and low sodium drinks)
Recreational athletes and women at greater risk
Dangerous and requires immediate medical attention
What are the ACSM guidelines pre exercise
5-10 ml fluid/kg (sodium, salt snacks)
More fluid if no/dark urine
What are the ACSM guidelines during exercise
Sufficient fluid to limit body mass loss and limit electrolyte imbalance (0.4-0.8 L/h)
> 2h - add sodium
>1h - may consider CHO addition
What are the ACSM guidelines post exercise
Rapid recovery <12h: Consume 1.25-1.5L for each kg/BM loss + sodium
More recovery time: resume dietary practices + extra plain water
Whats the role of sodium
Sodium plays a crucial role in ensuring effective maintenance or reassumption of fluid balance
