KINE305 Chapter 9: Water Requirements and Fluid Balance

What are the three main functions of water in the body?

1. it is necessary for chemical reactions

2. vapor pressure for thermoregulation

3. outstanding lubrication

What kind of nutrient is water?

macronutrient, also the most unstable of all nutrients

What is the gold standard for determining hydration status?

there is NO gold standard

intake of B vitamins could change urine color OR kidneys concentrate urine when it doesn’t sense sufficient water

Why do you need the right balance of salt and water in your blood?

osmotic pressure is based on water/salt levels 

if balance of tissue or blood is off, the flow could flow too strongly in one direction

What are ways to monitor hydration status?

1. skin elasticity

2. BW before and after exercising (BEST)

3. urine color

What can lack of water cause?

deficiency symptoms and failure to drink water for more than a few days can result in death

How much of body mass does water account for?

50-60% depending on variations due to body fat

How much water does lean body tissues and adipose tissue contain?

lean body mass contains about 75% water by mass, adipose tissue contains only about 5% water by mass

What can happen to body-temperature if exercise is prolonged?

increase which leads to progressive dehydration and loss of electrolytes

you can train to the point of reabsorbing sodium

How many liters of sweat can people lose during strenuous activity in a hot environment?

2-3 L of sweat per hour, about 4% BW loss

What percent of BW loss does performance start declining?

decline at 2%

medical problem at 4%

In what environment might someone be dehydrated without realizing?

in really dry environments because of the evaporation gradient

How much sweat can be lost at low ambient temperatures (about 10 degrees Celsius)?

it can exceed 1L per hour

How does dehydration cause cardiovascular issues?

less water —> less blood volume = heart has to pump harder

How does dehydration cause central nervous system issues?

brain temperature determines body function or even shut-down

At what temperature does stroke occur?

at 105 degrees core temp or higher

How can stroke be treated?

cold water submersion while swirling water
- you have 30 minutes to get them in water before brain damage occurs
- they can be taken out once their core temp drops to 103 degrees

What is the normal range of body temperatures?

36-38 degrees C (96.8-100.4 degrees F) at rest and 38-40 degrees C (100.4-104 degrees F) during exercise

At what temperature does central fatigue ensue?

39.5 degrees C (103 degrees F)

fatigue protects against damage since it shuts down further function

Where are central thermoreceptors located?

in the preoptic anterior hypothalamus

What takes priority for further output decisions in extreme temperatures?

HOT = maintaining brain temperature takes priority
COLD = skin temperature takes priority

Which hormones/cytokines are capable of influencing thermoregulatory responses?

estrogen, interleukin-1, and interleukin-6

What is the function of interleukin-1 and interleukin-6?

they are what drives a fever

What happens if you try to cool your body off at high body temperatures?

environmental instances: the body will cool off

protected instances (such as fever): the body will try even harder to keep itself heated up

What components lead to heat stroke?

high osmolality and high brain temp

How can training improve thermoregulation?

thermoregulatory effector responses must be adequately stimulated (i.e. sweating and increased skin blood flow)

this is done by exercising at a sufficiently high intensity (70-100% VO2 max) and increase body temperature above 39 degrees C (102.2 degrees F)

What are heat-shock proteins?

they protect proteins from denaturing; you can gain more the more you exercise/train

What are changes/adaptations for heat and hypoxia that occur from training?

1. lower resting body temperature

2. lower sweating and shivering threshold

3. increase in total amount of sweat production

4. increased size of existing sweat glands

5. increase in total blood volume and maximal cardiac output

6. maintaining constant body temperature

What are recommendations for heat acclimation?

1. heat acclimation sessions should last at least 60 minutes per day and induce an increase in body core/skin temperatures as well as stimulate sweating

2. train in the same environment as the competition venue or indoors in a hot room

3. 10 days of extreme exposures to adapt

How can you be better adapted to dehydration?

there are no adaptations to dehydration or accumulating water; exposure to dehydration does NOT make you better at being dehydrated

Ideally, how long should the heat acclimatization period last to maximize all benefits?

at least 2 weeks; full acclimatization can take months to years

What can minimizing heat exposure lead to?

it can make you even more vulnerable to heat, preventing acclimatization

What causes the difference in performance during physical activity?

dehydration causes greater cardiovascular and thermoregulatory strain

What is the BW loss percentage threshold for strength training?

5%

What is the BW loss percentage threshold for endurance training?

2%

Why does dehydration impair performance?

1. reduced blood volume and increased blood viscosity

2. reduced max. cardiac output and VO2 max

3. decreased skin blood flow, less convective heat loss

4. decreased sweat rate, less evaporative heat loss

5. decreased heat dissipation

6. increased core temperature and central fatigue

7. increased rate of muscle glycogen use, more rapid glycogen depletion

What is heat stress?

rises in sympathetic nervous activity causes skin and gut blood vessels to constrict; cellular hypoxia leads to the production of reactive oxygen species (ROS), which can lead to membrane damage

What is endotoxemia?

Reactive Oxygen Species causes peroxidation of lipids in cellular membranes, making them leaky

in the GI tract, this allows the passage of bacterial toxins from the gut into systemic circulation, leading to endotoxemia and a drastic fall in BP

What are the benefits of oral fluid ingestion?

1. helps restore plasma volume to near pre-exercise levels

2. prevents adverse effects of dehydration on muscle strength, endurance, and coordination

3. improves performance and endurance capacity in the heat

Why is relying on feeling thirsty as the signal to drink water unreliable?

a considerable degree of dehydration can occur before the desire for fluid intake is evident

What should you drink during exercise?

a solution with carbs as glucose (20-60g/L) and sodium (20-60mmol/L) and should not exceed isotonicity (290mOsmol/L)

Why should drinks NOT be hypertonic?

too much added carbs in a sports drink decreases the amount of water that can be absorbed

water is drawn out of the interstitial fluid and plasma into the lumen of the small intestine by osmosis

delays the restoration of plasma volume during exercise compared with the ingestion of a more dilute hypotonic drink

What are the benefits of adding sodium to drinks?

1. increase palatability

2. maintain thirst and promote drinking

3. prevent hyponatremia

4. increase rate of water absorption

5. increase retention of fluid

6. offsets sodium losses in sweat

What happens is there are falls in plasma volume?

reduced muscle blood flow

How does the ingestion of cool fluids help with heat capacity?

additional volume of fluid in the body adds to the body’s heat-storage capacity

the cool fluids absorb heat, preventing the need to sweat as much

What is the problem of hyponatremia?

an electrolyte imbalance caused by excessive water consumption; leads to mental confusion, weakness, and fainting

When can symptomatic hyponatremia occur?

when the plasma sodium concentration rapidly drops to 130mmol/L or less

the longer it remains low, the greater the risk is of developing swelling of the brain and accumulating extracellular fluid in the lungs

What are the main factors influencing the effectiveness of postexercise rehydration?

the volume and the composition of the fluid consumed

Why is plain water not ideal for postexercise rehydration?

it can cause a rapid fall in plasma sodium concentration and in plasma osmolarity

these changes reduce the stimulation to drink and increase urine output, both of which delay rehydration

How can optimal rehydration after exercise be achieved?

only if sodium lost in sweat is replaced along with water

plasma volume is more rapidly and completely restored in the postexercise period if some sodium chloride is added to the water consumed

What volume of fluid should be consumed to ensure complete rehydration?

a volume equivalent to at least 1.5 times the sweat loss