Lecture 6 - Fluid & Electrolytes Flashcards
proportion of water in humans
the adult body is about 60% (male) or 50% (female) water by weight
- individuals with obesity are about 40% water weight
- athletes are about 70% water weight
where is water located in the body (on a cellular level)?
- 2/3 of the body water is found inside the cell (intracellular water)
- 1/3 of body water is found outside cell (extracellular fluid), this includes blood plasma, lymph, cerebrospinal fluid, interstitial fluid, urine, and fluid inside the joints and eyes.
- fat is essentially anhydrous, having only a 5-10% water content
functions of water
- transports nutrients in solution
- blood transport nutrients and oxygen and waste tissue
- provides protection (lubrication, cleansing, cushioning)
- participates in biochemical reactions and provides medium in which these reactions take place
- helps regulate body temp
what is normal body temp? what happens when we exceed this number
- normal body temp is 36-38 celcius but may increase to 38 to 40 deg during exercise
- when body temp rises towards 39.5, central fatigue ensues
- further increases are commonly associated with heat exhaustion and occasionally with heat stroke
thermoreceptors
- sensory information about body temp is perceived and sent to central controller by nerves emanating from both deep-body and peripheral (Skin) thermoreceptors
- central thermoreceptors, located in hipothalamus are sensitive to changes in internal temp
- the “thermostat” is located in the preoptic anterior hypothalamus
how can fluid loss via sweat be a double edged sword
- it cools you down but in the exercise is prolonged, body temp increases and excessive sweating can lead to progressive dehydration and loss of electrolytes
- some ppl lose up to 2-3 L per hour of sweat during strenuous exercise
what happens (physiologically) with heat injuries
- heat injury is most common during exhaustive exercise in a hot, humid environment, particularly if you’re dehydrated
- rises in sympathetic nervous activity causes skin and gut blood vessels to constrict
- cellular hypoxia (lack of O2) leads to the production of reactive oxygen species (ROS) which lead to membrane damage
Endotoxemia
- the ROS (reactive oxygen species) causes perioxidation of lipids in cellular membranes, making them leaky
- in the GI tract, this action allows the passage of bacterial toxins (endotoxins) from the gut into the systemic circulation, leading to endotoxemia (blood poisoning) and a drastic fall in BP
- this can lead to tissue injury
how does training improves thermoregulation
- to obtain thermoregulatory benefits from training, people must adequately stimulate thermoregulatory effector responses, exercise must be at a sufficiently high intensity (70-100%VO2)
- acclimation to warm environments requires exercising in a hot environment, not just resting in that environment
what are the recommendations for heat acclimation
- athletes planning to compete in hot ambient conditions should heat acclimatize to obtain biological adaptations lovering physiological straning and improving exercise capacity in heat
- heat acclimatization sessions should lasst at least 60mins
- athletes should train in the same environment as the copetitions venue
- early adaptations are obtained within the first few days but the main physiological adaptations are not complete until around a week. Ideally, the heat acc. period should pass 2 weeks
relate dehydration to exercise performance
dehydrations during physical activity in the heat provokes greater performance decrements that similar activity in cooler conditions
- this difference is thought to be mostly caused by greater cardiovascular and thermoregulatory strain associated with heat exposure
preexercise hydration recomendations
relying on feeling thirsty is unreliable because dehydration can occur before the desire for fluid intake is evident
Absolute recommendations: drink approx 500ml of cluid 2hrs before exertion and another 500ml about 15mins before prolonged exercise
Relative recommendation: drink about 6-8ml of fluid per kg/BW about 2hrs before to allow sufficient time for fluid absorption
Pre-Exercise Hyperhydration benefits
hyperhydration (greater than normal body-water content) can improve thermoregulation by expanding BV and reducing plasma osmolarity, thereby improving heat dissipation and exercise performance
glycerol-induced hyperhydration
greater fluid retention is achieved if glycerol is added to fluids consumed before exercise
- when glycerol is consumed orally, it is rapidly absorbed primarily in the small intestine
- with supplemental glycerol ingestion, an incrrease in the osmotic gradient in the kidney nephrons occurs, resulting in better maintenance of hyperhydration
hydration during exercise
- where rehydration is the main priority, the solution should contain some carbs as glucose, glucose polymers, and sodium and should not exceed isotonicity (~300 mOsmol/L)
- too much added carbs, although provided fuel, decreases the amount of water that can be absorbed
- with hypertonic (see sl. 27 for chart) drinks, water is drawn out of interstitial fluid and plasma due to osmosis
- hypertonic solutions delay the restoration of plasma volume due to osmotic gradient
