Water Balance & Hydration Flashcards
Total body water percentage in a baby, adult female and male
Baby: 75%
Female: 50%
Male: 60
Water content in muscle
- Blood plasma
- Interstitial fluid
- Intramuscular fluid
Blood plasma: 7.5% TBW
Interstitial fluid: 30% TBW
Intracellular fluid: 62.5%
Water Balance regulation
- Nervous
- Hormonal
Anti-diuretic hormone (ADH)
- Primary effect is to decrease urine volume
Aldosterone
- Stimulates the absorption of sodium by the kidney
Osmolarity
- What is osmolarity
- Sodium
- Rise or fall in osmolarity will alter kidney function
- The number of solute particles (milliosmoles)
Sodium - major electrolyte in extracellular fluid, 50% of plasma osmolarity (290 mOsmol/L)
Rise or fall in osmolarity will alter kidney function
- Water excretion
- Water conservation
Kidneys
- Thirst
Conserve water or electrolytes but they cannot restore fluid levels
Thirst
- Evoked by the detection of elevated plasma osmolarity and, to a lesser extent, by reductions in blood volume and pressure
- ↑Secretion of antidiuretic hormone (ADH)
- ↓ urine excretion
Hyponatremia
- Symptoms
- Plasma sodium concentration
- Very low sodium levels
Symptoms:
- Mental confusion
- Weakness
- Fainting
- Normal plasma sodium concentration: 140 to 144 mmol/L
- Symptomatic: 130 mmol/L or less
- Well below 120mmol/L - risk of brain seizure, coma, and death increases. The longer that it remains low, the greater the risk is of developing swelling of brain and accumulating extracellular fluid in the lungs
Thermoregulation
- Normal vs exercise
- Heat stroke
- Environmental heat stress
- Controlled by what
- Mechanism that prevents a rise in body temperature
- Normal (36 - 38 Celsius)
- Exercise (38 - 40 Celsius)
Heat stroke (due to rise in temp) - Life-threatening, characterized by lack of consciousness after exertion and clinical symptoms of damage to the brain, liver and kidney
Environmental heat stress
- Ambient temperature
- Relative humidity
- Wind velocity
- Solar radiation
Controlled by the hypothalamus
- increase blood flow to skin and increase sweat response to decrease core temp
Heat Transfer
- Convection (transfer of heat through fluid or gas)
- Conduction (Transfer of heat through direct contact)
- Evaporation (Heat loss through water vaporization from skin)
- Radiation (transfer of heat through electromagnetic waves)
When skin temp is higher then environment (heat loss)
- Evaporation
- Convection
- Conduction
Environment temp is higher than skin (heat gained)
- Convection
- Conduction
Thermoregulation and exercise
- Heat production during exercise
- What happens to the heat
- Hypothalamus
- Can we improve your thermoregulatory response?
Heat production during exercise
- 1L of oxygen consumed during exercise = 16kJ (4kcal) of heat is produced -> mechanical work
What happens to the heat
- Some lost from overlying skin
- Passed to body core through venous blood flow returning to the heart
Hypothalamus
- Thermoreceptors -> detect changes in core body temp
- Received sensory input from skin thermoreceptors
- Produces effector response
- Increase in skin blood flow
- Initiates sweating
Can we improve your thermoregulatory response?
- Yes by training at high intensities
- Intensity 70-100% VO2 max
- Increase body temp above 39 degrees
Adaptation of exercise
- Earlier onset of sweat secretion
- Increases total amount of sweat
- Increases the sensitivity of the relationship between core temp and swear rate (threshold for sweat decreases)
- Hypertrophy of sweat glands without increasing total number
- No adaptation with dehydration
Dehydration
- What is dehydration
- Body’s response to dehydration
- Thermoregulation and Exercise
- At what level of Dehydration is performance affected
- Fluid loss (%)
- Effects of Dehydration
- Reduction in body’s water intake
Response
- For every liter of water lost
- Increased HR by 8 bpm
- Decrease cardiac output by 1 L/min
- Increase core temperature by 0.3 degrees C
Thermoregulation and Exercise
- If dehydrated during exercise
- Body temperature to rise faster
- Elicit higher HR
At what level of Dehydration is performance affected
- Fluid loss of 2% of body mass
1% - Thirst threshold, and threshold impairment thermoregulation - ↓ in performance
2% - Stronger thirst, vague discomfort, not as hungry
3% - Dry mouth, ↓ in urine output
4% - 20-30% ↓ in performance
5% - Concentration goes, headache, impatience, sleepiness
6% - Serious health problems
Effects of Dehydration
- Reduction in blood volume
- Decreased skin blood flow
- Decreased sweat rate
- Decreased heat dissipation
- Increased core temperature
- Increased rate of muscle glycogen use
Pre-exercise Hyperhydration
- Hyperhydration and effects
- Temporary hyperhydration
- Dehydration Recommendation
Hyperhydration: maximize total body water content
- Improve thermoregulation
- Expanding blood volume
- Reducing plasma osmolality
- Improving heat dissipation and exercise performance
- Reducing the thermal and cardiovascular strain of exercise
Temporary hyperhydration
- Large volumes of water or water-electrolyte solutions
- 1-3 hrs prior to exercise
- GI discomfort
- Much of the fluid overload is excreted
- Greater fluid retention is achieved by adding glycerol (WADA prohibited list in 2010 but was removed)
Dehydration Recommendation
- 5-10ml/kg BW 2 to 4 hours prior exercise
Fluid intake during exercise
- Fluid intake & fluid loss
- Sweat rate
- Fluid intake during strenuous exercise of less than 30 minutes offers NO ADVANTAGE
- Exercise that lasts longer than 1 hour or for exercise in hot or humid condition, consumption of carbohydrate - electrolyte sports drink is warranted
- Regular water intake during prolonged exercise
- Improves performance & exercise capacity
Dehydration can be avoided by matching fluid intake with fluid loss (sweat)
- Very difficult because
- Strenuous exercise sweat rates can be 2-3 L/h
- Difficult to know specific amount
Sweat rate
- Environmental conditions
- Intensity
- Individual differences
- Duration
- Warm environment - 2-3 L/hr
- Low ambient temp (12 C) - 1 L/hr
- Water replacement more important than electrolyte replacement
Fluid intake during exercise
- Hot condition
- Hypertonic, Hypotonic & isotonic
- Fuel intake
- Sports drink
- Sodium & electrolytes in sports drinks
- Typical ingestion rate
Sweat rate almost 2 x greater when exercise is performed in hot and humid conditions
Hypertonic
- More solute -> water will move out of cell
Hypotonic
- Less solute -> water will move into cell
Isotonic
- Same solute -> concentration is equal - net movement is zero
Fuel intake (simple CHO) - Too high: negative affect on water absorption as water will be drawn out of the interstitial fluid and plasma and into the intestine to aid in digestion of CHO is this is known as a hypertonic solution
Sports drink
- Are either hypotonic or isotonic
Sodium and electrolytes are added to sport drinks to:
- Increase palatability
- Maintain thirst (and therefore promote drinking)
- Prevent hyponatremia (low serum sodium concentrations, which can occur if you consume too much water)
- Increase the rate of water uptake
- Increase the retention of fluid
Ingestion rates
- 0.4 - 0.8 L/hr
- CHO 6 - 8% hypotonic solution
Rehydration after exercise
- Factors that influence the effectiveness of post-exercise rehydration
- Volume as a percentage
- Guidelines
Factors that influence the effectiveness of post-exercise rehydration
- Volume of fluid
- Fall in plasma sodium levels and plasma osmolality
- Reduce the sensation to drink
- Increases urine output = delay in the rehydration process
- Consumption of fluid
- Sodium added to water helps
- Promotes rapid fluid absorption in the small intestine
- Plasma sodium levels remain elevated - helps maintain thirst while delaying the stimulation of urine production
- Optimal rehydration: sodium lost in sweat is replaced along with water
Volume as a percentage
- Just matching water content that was lost (100%) is not as beneficial as drinking more (150-200%)
Guidelines
- 125 to 150% of the fluid lost at a moderate rate
- Include sodium
