Hydration Flashcards
What is euhydration?
- A normal state of body water
- Deviations from this norm result in compensatory responses
What is hyperhydration?
A sustained increase in body water (although often transient). You can extend hyper hydration with glycerol or salt.
What is hypohydration?
A sustained decrease in body water ie. sweat more than you drink
What is dehydration?
- The process of losing water
- Not a state of low body water
How is body water controlled?
Tightly controlled through thirst and the kidney regulation of urine
What is the daily variation of body mass?
less or equal to 1%
What are the things that affect the loss of water balance?
- Sweat
- Urine
- Respiratory
- Faecal
What are the things that affect the gain of water balance?
- Metabolic water production (contracting muscles produces water)
- Food
- Drink
What are the important time points for hydration?
- Pre exercise
- During exercise
- Post exercise
What are the measures of pre exercise hydration?
- Urine osmolality
- Serum osmolality
- Urine specific gravity
- Urine colour
What is urine osmolality?
- Euhydrated <700 mOsmol/kg
- Accuracy needs first void sample
- Expensive
What is serum osmolality?
- Euhydrated ~285 mOsmol/kg
- Accuracy gold standard
- Expensive
What is urine specific gravity?
- Euhydrated <1.020 mg/cm^3
- Relatively cheap and quick results
- Accuracy needs first void sample
What is urine colour chart?
- Euhydrated <3 on scale
- Very cheap and quick results
- Good education tool
- Accuracy needs first void sample
- Affected by other dietary components
What does research on hydration status tell us?
Realise that there is huge variation in hydration status so there is never a on size fits all approach
Are there effects of starting hypohydrated?
Some association with being hypo hydrated and finding the training harder (huge variation though)
What are the pre-exercise guidelines?
- Start exercise in a euhydrated state
- Slowly drink 5-7ml/kg at least 4h before exercise
- If urine still dark, drink a further 3-5ml/kg 2h before exercise
- Think about urination - drink composition?
- Sodium helps with fluid retention
- Drink temperature is important in the heat
What are the effects of dehydration?
- Depends on the event
- Decrease in skill performance
- Decrease in mental performance
- Opening of the blood brain barrier (effects your cognitive performance)
- Increased perception of effort
What dehydration levels have successful athletes shown to have?
5-8%
How to measure sweat loss?
- Sweat loss = Body mass + fluid intake
- Sweat loss (l/h) = (Body mass + fluid intake x 60) / time (mins)
How to measure dehydration?
Dehydration = (body mass loss / initial body mass ) x 100
Note: if you can weight you are not dehydrated
What are athletes perception of fluid balance?
- They are losing a lot more water than they think they are
- Athletes and adults engaging in exercise underestimate sweat losses by around 40-50%
What is overhydration?
- Increase in body mass
- Urination
- Dilution of blood sodium concentrations
- Hyponatremia?
What is hyponatremia?
- Usual serum Na concentration is 135-145 mmol/L
- Severe health consequences
- Symptoms include: fatigue, lethargy, brain aneurisms and death
- Incident in endurance events 10-40%
What are the risk factors of hyponatremia?
- Exercise duration >4h
- Slow speeds
- Females
- Low body weight
- Excessive fluid intakes
- Non-steroidal anti-inflammatories
- Extreme environments
What are the ACSM drink guidelines?
- Try to limit dehydration to <1-2% loss in body mass
- In hot environments this may not be feasible, in this case try to minimize dehydration
- Avoid gaining weight
What is the reported loss of starting weight in a marathon?
9.8%
What is the main electrolyte lost in sweat?
Sodium: 20-80mmol/L
How do you calculate salt losses?
Sodium loss = sweat concentration x sweat loss
Why include sodium in the diet?
- Improve palatability
- Maintain extracellular volume
- Might attenuate the decline in blood sodium
Why is palatability important?
- Increasing palatability could increase fluid intake thereby delaying onset of dehydration
- But large amounts of salt decrease palatability
- Fluid intakes are greatest with 30mmol/L NaCl concentration
What did the study of saltiness and exercise find?
- That when you are exercising, the preference of saltiness increases
How does sodium ingestion promote fluid intake?
- Increasing thirst
- Delaying dehydration
How does sodium effect the body?
Sodium is important for intestinal absorption, however, the inclusion of sodium in a drink does not have a large effect on gastric emptying or intestinal absorption
Are sports drinks or salt capsules better?
Sports drinks contain 20-40mmol/L. Salt capsules would negate the problem of taste but some actually contain less sodium than sports drinks
What are the recovery guidelines?
- Rehydration: restore electrolyte and fluid balance. 1.5*body mass loss
- Repair: muscle repair and regeneration. 20-30g protein
- Restore: muscle and liver glycogen levels to those pre-exercise. ~1-1.2g/kg/h CHO during first 4-6hours
Is larger or smaller volumes of fluid best?
Sipping retains more in the body than drinking a lot in one go. Smaller, regular volumes work best because otherwise you end up overloading your system
What factors influence fluid balance?
- The volume you are drinking
- How quickly you drink
- The contents of the drink
What does the addition of CHO to rehydration drinks do?
Enhances fluid retention if the concentration of CHO (6-10%) and volume of fluid (150%BM loss) ingested are sufficiently high
