Fluids, Hydration and Sport Performance Flashcards
“normal” body watercontent within the homeostatic range
* The in and out of water are aligned
Euhydration
What is the range in euhydration is sustained?
± 2%
How much water makes up body mass?
~60% of body mass (range = 50-70%)
What happens to water with weight loss?
weight loss = acute fluid loss
* 1lb lost = ~ 500mL (not replaced)
* heat and water are factors of fluid loss
What does hydration support in sport?
- cardiovascular function (blood pressure)
- body temperature regulation
- sport performance
What is water important for?
- waste excretion
- blood volume & pressure regulation
- transport of oxygen & nutrients
- heat transfer
What are some factors that influence hydration?
- training status and intensity (well trained = more efficient at cooling so less loss)
- humidity
- temperature
- environment and equipment (venting of clothing)
The proces of dynamic loss of body water- e.g., the transition from euhydration to hypohydration
* losing
dehydration
The process of dynamic gain of body water (via fluid intake) - e.g., the transitionfromhypohydration ot euhydration
* adding
Rehydration
state of body water deficit
hypohydration
state of body water excess
over- or hyperhydration
prevalence of hypohydration and what happens
hypo is more common than hyper and can impair performance especially if it excees 2-3% body mass loss and in hot/ humid conditions
* cognition: cloudy thinking
* team sports: missing, tripping, balance
* aerobic performance: slower, sluggish
* muscle endurance, strength and anaerobic power impaired
What is sweat rate?
fluid loss/ hour
What influences fluid losses?
The climate - temperature and humidity - around and athlete influences fluid losses at all paces and intensities
What are the phases of hydration
Want as minimal losses as possible (ideally <1% body weight) and different issues can impact hydration at each of these phases
1. intake
2. absorption
3. distribution
4. retention
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 cardiovascualr function during exercise via better maintenace of plasma volume
- promotes whole-body rehydration by stimulating fluid retention (decreased urine loss)
general population vs. athletes sodium intake
general population want to decrease sodium intake, but athletes are an exception especially endurance since it replaces what is lost in sweat
Physiology of hypohydration?
hypohydration → hypovolemia & hyperosmolality → ↑cardiovascular strain & ↑body core temperature → ↑ fatigue
decreased ECF (plasma) volume
hypovolemia
increased plasma osmolality (concentration of dissolved solutes, mostly sodium, in the blood)
hyperosmolality
what happens with ↑ CV strain?
lower stroke volume and higher heart rate
What happens with ↑ body core temperature
dereased ability to dissipate body heat through sweatring and skin blood flow
* cant cool off - no sweat, hot to the touch and can worsen of not treated
What does hypohydration impair?
Impairs the ability of the body to remove heat leading to
* CV strain
* increase glycogen use
* altered metabolic and CNS function
* decreased fluid absorption
* risk of heat illness
result of >2% fluid loss
hypohydration
* Impaired cognitive function and aerobic performance
result of 3-5% fluid loss
Decreased anaerobic/high-intensity performance, sport-specific skills, cool-weather aerobic performance
* some people goiing because of competitiveness but dangerous
How common is hypohydration in sport?
very common and most are below sweat rate goal (not matching in and out) but most athletes end a workout in a state of dehydration that will eventually be corrected by drinking and eating post-exercise
A low blood sodium concentration ([Na+]) that develops during or immediately following physical activity (sport or recreation).
Exercise-associated hyponatremia (EAH)
What is the diagnostic threshold for hyponatremia?
any blood [Na+] below 135 mmol/L regardless of the presence or absence of signs and symptoms.
* Women may be at greater risk than men.
Highest risk for EAH
ultra-endurance athletes who practice overzealous fluid consumption coupled with low sodium intakes before, during, and after sport.
* swelling in the brain
* Non-osmotic AVP stimulation is also a factor
Physiology of overhydration
- Overconsumption of low or no-sodium fluids; leads to
- Overhydration; leads to
- Exercise Associated Hyponatremia (EAH); leads to
- Water flux into the ICF
body mass gain because of a fluid surplus
overhydration
Addition risk factors of overhydration with increased fluid intake
- prolonged exercise (>4 hours)
- smaller individual (low baseline total body water)
- excessive sodium loss (sweat)
dilution of plasma sodium concentration to < 135 mmol/L
EAH
What happens with Water flux into the ICF
cell swelling such as the brain
* the severity of symptoms related to brain cell swelling depends on how much and how fast plasma sodium [Na+] decreases
Types of EAH in Athletes
- Hypervolemic Hyponatremia
- Hypovolemic Hyponatremia
What drives Hypervolemic Hyponatremia
Driven by fluid overload
What drives Hypovolemic Hyponatremia
Driven by inadequate sodium intakes + excessive sodium losses +
hypohydration/dehydration
* excessive sweating
* excessive heat
Total body water and sodium content are decreased and the relative decrease in total body sodium is greater than the decrease in total body water
Hypovolemic Hyponatremia
Fluid condition that typically results in weight gain during activity
Hypervolemic Hyponatremia
Fluid condition that typically results in weight loss during activity
Hypovolemic Hyponatremia
Sodium difference between hypo- and hyper- volemic hyponatremia
- hypovolemic hyponatremia: sodium depletion
- hypervolemic hyponatremia: sodium dilution
Consequences of EAH in Athletes
Ultimately cerebral edema which has many symptoms
* brain swelling
* also hands and feet
Prevention of EAH in Athletes
- Training diet adequate, but not excessive, in sodium.
- Moderate fluid intake during preparation and competition (Sipping rather than chugging)
- Goal is very pale, coloured, yellow urine – not absolutely clear urine
- Use of a fluid replacement beverage that contains sodium during sport lasting > 1 hour (H2O, CHO, electrolytes; not energy drinks)
- Practice fluid replacement regime during training.
- Weigh in before and after to assess weight changes
- Look for signs of fluid retention driven by AVP stimulation
- Swollen hands/fingers and feet
AVP
arginine vasopressin OR anti-diuretic hormone (ADH)
Water DRIs
- The values do NOT consider extraordinary amounts of physical activity.
- Water to support physical activity is ABOVE the DRI recommendations.
Treatment of EAH
- stop water drinking
- add sodium
- need medical help
Risk factos of EAH in athletes
- females increased risk of ADH effects altered
- short stature cant lose as much sweat
Sources of body water losses include:
- Urine (Greatest source of losses (1-2 L/day)
- Feces
- Perspiration (Sweat)
- Respiration
average total loss of water
Average total losses = ~2.5 L/day from all sources under “normal,” conditions.
What happens to water balance and losses with strenuous work?
- loss through urine decreases
- loss through sweat increases
What does normal water balance look like?
Water output of normal vs. exercise
Water Intake: Normal vs Exercise
Effect of Physical Activity on Fluid Losses
- Physical Activity increases fluid losses: In general as the duration OR intensity of activity increases, so to does the amount of fluid lost.
- Exercise increases metabolic rate by 5 to 20 times above resting conditions: Increases in metabolic rate generate heat that must be dissipated in order to maintain normal body temperature of ~37°C
Effect of Physical Activity on Sweat Production and Fluid Losses
- Environmental Conditions (Temperature, humidity, Humidex, wind speed, radiant load)
- Clothing and Equipment
- Exercise Intensity and Duration
- Athlete’s Level of Physical Conditioning
- Age and Gender
Thirst and fluid factors
- physiological thirst (sensation)
- percieved thirst (perception)
- beverage
association of Thirst, hydration, and ADH
The threshold for thirst lags behind body hydration changes and therefore, it lags behind an athletes’ true fluid needs.
* feel thirst too late
Impact of dehydration on pace
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.
When is drink to thirst okay?
- Short duration activities < 60 to 90 min
- Cooler conditions
- Lower intensity
When should planned drinking be used?
- Longer duration activities > 90 min (but use in short if high comp.)
- Particularly in the heat
- High intensity
- High sweat rates
- When performance is a concern
- When carbohydrate intake of 1 g/min
What should planned drinking look like?
drink consistently every 10-15 min for long endurance activites
* do training trial first with fluid and electrolyte replacements
Where is voluntary dehydration might occur?
Restriction fluids to reduce weight
* A common (and risky) practice in body-building, jockeying, and other weight-class sports
Effects of dehydration
2% is the cut-off for euhydration
Heat related disorders associated with dehydration
- heat cramps (least severe)
- heat exhaustion
- heat stroke (extreme - no more sweat)
Planned overconsumption of water
Voluntary hyper-hydration
What might the goal of Voluntary hyper-hydration be?
prevent dehydration
* Sometimes practiced in conjunction with supplemental Glycerol to hold on to it
What might the goal of Voluntary hyper-hydration be?
prevent dehydration
* Sometimes practiced in conjunction with supplemental Glycerol to hold on to it
What does glycerol retain water?
Glycerol-containing beverages create an osmotic gradient in the circulation favouring fluid retention which has been purported to facilitate hyperhydration and protect against dehydration.
GIH
Glycerol-Induced Hyperhydration
Risks of GIH
Associated with risks and side effects that must be considered!
* Nausea
* gastrointestinal discomfort
* light-headedness.
* Potential effect on pace/speed r/t carrying excess BW
Does WADA allow GIH?
Hemodilution associated with glycerol-induced fluid retention in the vascular space can mask illegal doping practices. As a result, glycerol is listed as a prohibited substance by the World Anti-Doping Agency (WADA).
FACTORS IN GASTRIC EMPTYING
- Gastric volume
- Carbohydrate type (simple/ complex)
- Body position (slow in laying down)
- Beverage osmolality
- Energy content
- Electrolyte content
- Exercise intensity (intense = slow)
- Beverage pH
Ideal energy density of a beverage
6-8% CHO (energy drink is 30%)
What influences fluid absorption?
Gastric Emptying Time and Volume
* The goal is to have beverages move through the stomach and be absorbed as quickly as possible
* large amounts all at once decrease emptying
* complex CHO dont clear fast
When to Add Carbohydrate and how much
If an athlete is training or competing for 60 minutes or longer with a performance goal
* Add 30-60 g/h carbohydrate, resulting in no more than a 6% solution (6% = 14 g/250 mL)
* Choose quickly oxidized carbohydrates to provide energy and minimize GI upset
FLUID RETENTION & THE IMPORTANCE OF SODIUM
Fluid Volume and Rehydration
Use body weight as guide
* Replace 150% of fluid loss if Sweat Rate is not calculated
* 1200-1500 ml/kg body weight
* Sodium critical for complete rehydration
intestinal water absorption
Why is Exercise Associated Muscle Cramps a hot topic?
The cause and treatment of exercise- associated muscle cramps (different from whole-body cramping) is not well understood
* Some cramps may be associated with disturbances of water and salt balance, but not all
* When water and salt losses are high, drinks containing electrolytes, especially sodium, should be used rather than plain water
Sources of fluid
- Water
- Fluid Replacement Beverages
approximate fluid loss during and after sport
- ~1000 ml/kg lost during
- ~1200-1500 ml/kg lost after
hydration reccomendations
- Before: Drink ~5-7 mL/kg of fluids with sodium ~4 h prior and another 3-5 mL/kg ~2 h prior if athlete cannot urinate or the urine is dark
- During: Amount of fluid based on sweat rate
- After: 1200-1500ml/kglost
Which fluid and when?
- PA <1 hour: plain cool water
- PA >1 hour or repeated bouts of <1h multiple time a day: trial fluid replacement that has H2O+CHO+electrolytes (gatorade/powerade)
