Chapter 11 - Hydration

Question 1

water in the body

Answer 1

• the body is 60% water by weight
• blood is 90% water
• 2/3 of body water is found inside cells (intercellular fluid) - 1/3 is found outside cells (extracellular fluid)

Question 2

cerebrospinal fluid

Answer 2

fluid that surrounds the brain and spinal cord

Question 3

interstitial fluid

Answer 3

fluid located between cells

makes up 1/3 of total body water, the other 2/3 are inside cells

Question 4

fluid balance

euhydration

Answer 4

conditions where water intake and water loss are matched, the body remains in a state of fluid balance

Question 5

fluid balance

hyperhydration

Answer 5

a sustained increase in total body water

Question 6

fluid balance

hypohydration

Answer 6

A sustained decrease in total body water

Question 7

fluid balance

dehydration

Answer 7

the process of water loss

Question 8

what 3 factors contribute to total water balance in the body

Answer 8

1. ingested fluids
2. food (mainly fruits and vegetables)
3. the breakdown of macronutrients to create energy results in the formation of water, which provides approximately 14% of daily water requirements.

Question 9

water output

Answer 9

1. feces and urine (1,300 mL per day)
2. evaporated through the skin (we weat out around 600mL per day)
3. exhaled as water vapor (300mL per day)

The body cycles at least 2.2 L of water per day, NOT ACCOUNTING for exercise water loss

Question 11

fluid balance during exercise

thermoregulatory sweating

Answer 11

The process of sweating to reduce core body temperature.

whole-body sweat rates can range between 0.25 to 3.0 L/h and can vary greatly among athletes

Question 12

sweat loss in athletes

Answer 12

there is large variability in whole-body sweat rate among athletes, which ranges from 0.25 to 3.0 L/h. Furthermore, these data also demonstrate clear differences between sports (highest in American football)

Question 13

micronutrients in sweat

Answer 13

sodium
pottasium
magnesium
calcium

Question 14

sweat sodium

Answer 14

sweat sodium losses are also highly variable and range from 10 to 150 mmol/h. Knowledge of sweat sodium concentrations, however, has limited utility in isolation and must be combined with the athlete’s sweat rate information to determine the absolute amount of sodium lost through sweat. For example, an athlete may have low sweat sodium concentrations but still exhibit large sodium losses due to their high sweat rate. In contrast, if high sweat sodium concentrations are accompanied by low sweat rates, then total sodium losses may be relatively low.

Question 15

molecular weight

Answer 15

the weight of a given molecule

Question 16

Effects of Dehydration on Performance

hypovolemia

Answer 16

**A reduction in blood volume
**
Insufficient water intake or excess water loss through sweat can lead to hypohydration, which results in decreases in blood volume

results in depleted caridac volume

Such symptoms increase physiological strain on the body in accordance with the level of dehydration. The reduction in blood volume, alongside a reduction in plasma volume, increases the viscosity of the blood and subsequently reduces the amount of blood returning to the heart due to the drop in central venous pressure.

Question 17

plasma volume

Answer 17

The total volume of blood plasma or fluid

Question 18

viscocity

Answer 18

the state of being thick

Question 19

central venous pressure

Answer 19

Blood pressure within the venous compartment

Question 20

diastolic pressure

Answer 20

The phase of the heartbeat when the heart relaxes and allows the chambers to fill with blood

Question 21

endurance sports

hypohydration in endurance exercise

Answer 21

• a decrease in blood volume and reduced cardiac output
• thus reducing oxygen delivery to working muscle tissue as noted earlier
• hypohydration is also associated with an increased rate of glycogen breakdown within skeletal muscle, which may contribute to the onset of fatigue during prolonged exercise.

Again, the general consensus is that hypohydration of 2% of body mass is sufficient to impair endurance performance across a range of exercise modes

Question 22

hypohydration and cognitive function

Answer 22

it is thought that the symptoms of hypohydration—such as thirst, headaches, and negative mood states—may distract from the task at hand and subsequently impair performance.

For example, reductions in reaction speed, vigilance, memory, and decision making have all been observed as a result of hypohydration, although the impact of such changes on skill-based performance outcomes remains equivocal

Question 23

hypohydration in strength and power

Answer 23

In relation to muscle strength, hypohydration appeared to have a greater impact on upper body strength assessments, which declined by an average of 6.3% compared to a 3.7% decline in the lower body

Interestingly, observed declines in muscle performance due to hypohydration appear to be greater in untrained individuals compared to those who are better trained

Question 24

A drop in what percentage of body mass is sufficient to begin to see impairments in sports performance?

Answer 24

2%

Question 25

estimating hydration status

WUT method

Answer 25

1. morning scale weight
2. thirst perception
3. urine color

Losses of >1% of body weight, persistent thirst or dark colored urine may indicate possible dehydration. If any two of these signs occur in the morning, dehydration is likely. If all three occur, dehydration is very likely

Question 26

rehydration strategy

Answer 26

achieved by consuming fluid at a rate of 150% body mass losses, adding sodium to reduce urine output, and monitoring symptoms regularly and consistently

Question 27

hydration status

urine color

Answer 27

when combined with alterations in body weight and the perception of thirst, can provide an indication of their hydration status

Question 28

hydration status

thirst

Answer 28

A conscious desire for water occurs during periods of body water deficit. Although the absence of thirst does not indicate euhydration, the desire for water does coincide with dehydration and should be combined with body weight and urine to provide an indication of fluid balance

When working with athletes, a simple Likert scale can be used to provide an objective thirst score

Question 29

sweat testing protocol

Answer 29

Question 30

athlete fluid intake recommendations

Answer 30

Current consensus recommends that good hydration practices include: (1) beginning exercise in a state of euhydration, (2) preventing excessive hypohydration during exercise, and (3) replacing fluid losses following exercise prior to the next exercise bout

sweat and hydration rates are highly individual

Question 31

pre-exercise hydration

Answer 31

Athletes should aim to commence exercise in a euhydrated state to minimize the potential adverse effects of fluid losses during exercise

consuming a sodium-rich meal can also contribute to stimulating thirst before a contest, which will help with the desire to replace lost fluids

Question 32

peri exercise hydration

Answer 32

As fluid losses during exercise are highly individual and can be influenced by a multitude of factors, fluid intake recommendations should be tailored to each individual athlete

Given that body weight losses of greater than 2% during exercise can impair both health and performance, athletes should drink sufficient amounts to replace sweat losses and limit body mass losses to 2%

Question 33

hyponatremia

Answer 33

Low sodium concentration in the blood.

Question 34

post-exercise hydration

Answer 34

Replacing fluids during the recovery period after exercise is an important consideration for all athletes. The two key factors that influence the effectiveness of the post-exercise hydration strategy are
1. volume
2. composition of the fluid consumed.

Question 35

fluid volume

Answer 35

It may seem logical to match post-exercise fluid intake with that lost during exercise, as calculated from the athlete’s sweat rate assessment. This amount, however, is insufficient because it does not account for further urine losses that occur in the hours following exercise

current guidelines recommend that athletes consume 150% of fluid losses during the recovery period to replace fluids lost during exercise

Question 36

fluid composition

Answer 36

ingestion of water alone results in a decrease in sodium concentrations within the body and results in a reduced perception of thirst and increased urine output. When combined together, these two factors will only serve to delay the rehydration process.

With this in mind, the addition of sodium into the rehydration drink plays an important role by increasing the desire to drink while also ensuring the fluid being consumed is retained within the body and not simply lost through urine

Question 37

sweat loss equation

Answer 37

Whole body sweat losses can be calculated using the following equations:

Equation 1: Sweat loss (L) = (Pre-exercise BM – (Post-exercise BM – fluid intake + urine output)

Equation 2: Sweat rate (L/h) = Sweat loss (from equation 1) / exercise duration

Question 38

calculating total fluid intake required

Answer 38

If an athlete has a predicted sweat rate of 1.25 L per hour after sweat testing, a planned hydration strategy would aim to provide fluid intake recommendations to prevent 2% dehydration. Across a three-hour event, this would equate to a total fluid loss of 3.75 L or 5.7% of BM. As such, the athlete’s hydration plan would prescribe fluid intake that aims to prevent dehydration above 2%.

This can be achieved by calculating fluid losses required for a 2% loss of body mass and subtracting this from the predicted fluid losses at 5.7% BM. In this example, a fluid intake of 2.45 L (0.82 L/hour) would be required to prevent dehydration above 2% body mass.

Event details: Three hours in duration

Estimated total sweat loss: 3.75 L (1.25 L/hour)

Estimated body mass loss: 3.75 kg

% BM loss at 65 kg: 5.7% (3.75 / 65) * 100

Fluid losses required for 2% BM loss: 1.3 L

Total fluid intake required: 2.45 L (0.82 L/hour)