Module 6 - Fluids and Hydration Flashcards
How much of your body is made up by water?
- Total body water is ~60% of body mass (Range = 50-70%)
Why is total body water important?
Waste excretion, blood volume and pressure regulation, transport of oxygen and nutrients, heat transfer
How much water is lost per pound during acute weight loss in sport?
- Acute weight loss in sport due to water loss NOT body fat
- For every pound of weight lost = 500mL of water lost and not replaced
Define euhydration?
“Normal” body water content within the homeostatic range
Define dehyration
The process of dynamic loss of body water - e.g. the transition from euhydration to hypohydration
Define rehydration
The process of dynamic gain of body water (via fluid intake) - e.g. the transition from hypohydration to euhydration
Define hypohydration
State of body water deficit that causes functional limitation in body
Define over- or hyperhydration
State of body water excess
Do dehydration and hypohydration mean the same thing?
- No, in practice people often use them synonymously but they mean different things
- Dehydration is the process of losing body water whereas hypohydration is when you are in a state of body water deficit
At what percentage is someone considered hyperhydrated or hypohydration?
- +2% total body water is hyperhydration or overhydration
- -2% is hypohydration and can lead to decreases in sport performance
How can hydration impact performance?
- Impacts cognition (processing slow/difficult)
- Team sports
- Aerobic exercise
- Muscle endurance, strength, and anaerobic power
- Hypohydration can impair performance especially if exceeds 2-3% body mass loss and in hot/humid conditions
Start to make little mistakes in sport, can’t control their body in a way they normally could. Individuals usually notice first.
What is humidex?
- High temperatures and humidity have greater effects on the body
- Harder to cool because no evaporation can happen (cooling is when sweat evaporates)
- Easier to recognize heat when it is dry compared to humidity
Why should you hydrate?
Hydrate to support…
- Cardiovascular function (changes blood volume/pressure which changes mechanics of CV system and renal system)
→ More hypohydrated = more profound effects
- Body temperature regulation
- Sport performance
What factors may influence hydration?
- Training status and intensity - well trained are more efficient at cooling/perspiration. Intensity increases temperature so more fluid lost at high intensity
- Humidity
- Temperature
- Environment and equipment - increased equipment harder for sweat to evaportate or dryfit temperatures harder to tell if you are sweating.
Sweating can be a cue for drinking. Dry fit = can’t tell sweating and may not drink as much water
How does sweat rate increase with hot and humid environments and running speed?
- Increased intensity will increase sweat rate
- Hot and humid will increase sweat rate further compared to cool and dry
Define sweat rate
Amount of fluid you are losing per hour
What are the four phases of hydration?
- Intake
- Absorption
- Distribution
- Retention
Different issues can impact hydration status at each of these phases
What is the role of sodium in fluid balance?
- Stimulates thirst - leading to increased fluid intake and better maintenance or restoration of euhydration
- Helps maintain proper fluid and electrolyte balance among fluid compartments
- Supports cardiovascular function during exercise via better maintenance of plasma volume
- Promotes whole-body rehydration by stimulating renal fluid retention (decreased urine loss)
Should athletes be consuming salt?
General population needs to reduce intake but need to have some for athletes! Electrolyte drinks important
What occurs to physiology during hypohydration?
- Hypohydration - total body water deficit >2% →
- Hypovolemia - decreased ECF (plasma) volume →
- **Hyperosmolarity **- increased plasma osmolality (concentration of dissolved solutes, mostly sodium, in the blood) →
- Increased cardiovascular strain - lower stroke volume and higher heart rate
- Increased body core temperature - decreased ability to dissipate body heat through sweating and skin blood flow (cannot sweat anymore)
- Increased fatigue - early onset of fatigue leading to reduced performance
How can athletes prevent hypohydration?
- Need to be drinking throughout entire day in off time. Cannot drink enough acutely in exercise for your body to make up for it
→ Setting themselves up for hypohydration if do not hydrate throughout the day!
What does hypohydration lead to?
- Hypohydration impairs the ability of the body to remove heat
- Leading to:
→ Cardiovascular strain
→ Increased glycogen use
→ Altered metabolic and CNS function
→ Decreased fluid absorption
→ Risk of heat illness
What occurs at 2% hypohydration versus 3-5% hypohydration?
- > 2% = impaired cognitive function and aerobic performance
- 3-5% = decreased anaerobic/high-intensity performance, sport-specific skills, cool-weather aerobic performance
Is hypohydration common?
- Most athletes end a work out in a state of dehydration that will eventually be corrected by drinking and eating post-exercise
- Need to work on preventing hypohydration before sport occurs
What is exercise associated hyponatremia (EAH)?
- Exercise-associated hyponatremia (EAH) refers to low blood sodium concentration ([Na+]) that develops during or immediately following physical activity (sport or recreation)
→ Can have fluid movement into the brain or swelling - The diagnostic threshold for hyponatremia is any blood [Na+] below 135 mmol/L regardless of the presence or absence of signs and symptoms
Who is at greater risk of EAH?
- Women may be at greater risk than men
- Highest risk is in ultra-endurance athletes who practice overzealous fluid consumption coupled with low sodium intakes before, during, and after sport
→ Non-osmotic AVP stimulation is also af actor
What is the physiology seen with overhydration?
- Overconsumption of low or no-sodium fluid
-
Overhydration - body mass gain because of fluid surplus. Additional risk factors:
→ Prolonged exercise (>4 hours)
→ Smaller individual (low baseline total body water)
→ Excessive sodium loss (sweat) - Exercise Associate Hyponatremia (EAH) - dilution of plasma sodium concentration to <135 mmol/L
- Water flux into the ICF - the severity of symptoms related to brain cell swelling depends on how much and how fast plasma sodium [Na+] decreases
What are the two types of hyponatremia?
- Hypervolemic Hyponatremia
- Hypovolemic Hyponatremia
How are hypovolemic hyponatremia and hypervolemic hyponatremia related?
- Both lead to EAH
- Too much water can cause sodium dilution while too much sweat can cause sodium depletion
What are the consequences of EAH in athletes?
- Can have increased TBW, reduced urine output, sodium loss, and inadequate sodium intake
- Cerebral edema
- GI discomfort, Nausea and vomiting, Throbbing headache, Restlessness, Swollen hands and feet, Lethargy, Confusion, Wheezing, Seizures, Coma, Brainstem rupture, Death
What are the DRIs for total water per day?
- The values do NOT consider extraordinary amounts of physical activity
- Water to support physical activity is ABOVE the DRI recommendations
Values are meant to be across the entire day!
How does water balance in average adults vary under different conditions?
- increases with hot environment and strenous work
What does output and intake of water normally look like?
How does water output look different with exercise compared to normal conditions?
How does water intake look different with normal conditions versus exercise?
What are the types of thirst and the factors related to them?
Why should we not wait until we are thirsty to drink?
- The threshold for thirst lags behind body hydration changes and therefore, it lags behind an athletes’ true fluid needs
- Won’t notice thirst until it is too late. Need to encourage athletes to think about it and not the best indicator of fluid needs. Practice planned drinking!
- Plasma ADH will increase as plasma osmolality and thirst will increase
What will happen to racing pace when only listening to thirst cues?
- In general, the more dehydrated the athlete is, the slower their pace
- Insufficient drinking contributes to dehydration, if ad lib fluid ingestion, based on perception of thirst, is practiced
- Thirst is NOT the best indicator of fluid needs for all athlete groups
What are the effects of dehydration at different body weight losses?
What are the degrees of severity, signs and symptoms, and corrective actions of:
- Heat cramps
- Heat exhaustion
- Heat stroke
What percent should carbohydrate drinks be?
- 6% = too dilute
- 8% = concenrated and won’t leave stomach fast enough
How is sodium, glucose, fructose, and sucrose absorbed?
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