7. Hydration and exercise

what is the most abundant substance in the body

water

how much of the body is made up of water?

45-75%

distribution of water in the body depends on what 3 things?

• age

• sex

• body composition

how does age impact water in the body

% of total body water decreases with age 

how does sex impact water in the body

males typically have more body water than females (higher FFM)

how does body comp impact water in the body

muscle has more water than fat

muscle is ______% water

65%

fat is _% water

10-40%

what are the 4 functions of water in the body?

1. universal solvent

2. transport

3. lubricant

4. regulation of body temperature

water as universal solvent (what does it do, this mean?)

critical for majority of bodily processes including digestion, pH balance, and enzymatic reactions

water as transport for what (function)

water is the medium for the transport of oxygen, nutrients, and hormones to cells throughout the body.

water is also critical for what bodily function

removal of waste 

water as a lubricant (what body parts)

joints, eyes, mouth, intestinal tract

how does water function in body regulation (key word)

water is critical for regulating body temperature through sweating

how does water help regulate body temp? (3 steps)

1. Water in blood carries heat to the capillaries at skin surface

2. The heat is released at the skin surface. Evaporation of sweat cools the skin.

3. Cooled body returns to the body core

what 3 things contribute to water intake?

metabolism, food, fluid 

how much does it contribute to water intake? (ml)

• metabolism

• food

• metabolism

• metabolism= 300 ml

• food= 700 ml

• beverages= 1,500 ml

total—> 2,550 ml

what organs contributes to water output (4)

intestines, lungs, kidneys, skin

amount of water released (ml)

• intestines (stool)

• lungs (breathing)

• kidneys (urine)

• skin (sweat)

• intestines (stool): 100 ml

• lungs (breathing): 350 ml

• kidneys (urine): 1,500 ml

• skin (sweat): 600 ml

what is the most variable output of water?

sweat

define hyperhydration

fluid intake > fluid loss

define euhydration

fluid intake = fluid loss

define hypohydration 

fluid intake < fluid loss 

define dehydration

process of losing body water

define rehydration

process of replacing or regaining body water

define hydration**

 is process that starts with the ingestion of fluid, followed by emptying from stomach and absorption through intestines, then distribution of the fluid throughout body and finally retention or excretion by kidneys

4 steps of hydration:

1. fluid intake

2. fluid absorption

3. fluid distribution

4. fluid retention

fluid intake is __% from beverages?

70-80%

fluid intake is __% from foods

20-30%

what types of foods contribute a lot of water?

fruits and vegetables

define hypovolemia

decrease in the amount of water in the blood

when is physiological thirst stimulated?

by decrease in the amount of water in the blood (hypovolemia) and increase in plasma osmolality

during exercise, what occurs (relating to water content)

both hypovolemia and increased plasma osmolality occur during dehydration due to sweating

it is very important to note that physiological thirst occurs once

body is already dehydrated

threshold for thirst and body hydration

Threshold for thirst lags behind body hydration changes

how does thirst occur? (5 steps)

1. sweat loss decreases plasma volume, increasing plasma osmolality (increase Na and Cl)

2. baroreceptors sense changes and stimulate ADH (vasopressin)

3. kidneys conserve water and sodium

4. thirst centers triggered 

5. drinking helps restore levels 

what does sweat loss do to blood?

↓ plasma volume, ↑ plasma osmolality (plasma Na+ and Cl- ↑↑)

what senses changes in plasma volume and osmolality?

baroreceptors

what do baroreceptors do?

release ADH (vasopressin)

as a result to ADH, what occurs 

kidneys conserve water and sodium 

conservation of water and sodium from the kidneys causes what

thirst centers to be triggered causing thirst

what helps restore plasma levels?

drinking fluids

what is mild dehydration (% weight loss)

< 2% weight loss

mild dehydration effects on performance

 typically has no deleterious effects

what conditions may dehydrate athlete by >2-3% of body weight

prolonged vigorous intensity exercise ( > 2 hours) in warm temperatures (> 85 F)

prolonged vigorous exercise in warm temps (>85F) effect on performance?

can significantly impair performance

prolonged vigorous exercise in warm temps (>85F) impairs performance due to? (2)

increase H2O and electrolyte loss

what is considered significant dehydration (% weight loss) 

>2%

Significant dehydration (> 2% body weight losses) has been found to impair

performance in the heat

in what conditions has significant dehydration (3-4% body weight loss) seen to  impair aerobic performance, as well as cognitive performance and technical skill in certain team sports

cooler conditions…

at what temps is performance seen to be impaired?

>85F

Exercise in warm weather ( > 85 F) impact on fluid?

increases fluid losses (x 50)

how should fluid goals for athletes be set

ALWAYS individualized (not one amount for everyone)

fluid needs differ based on (5)

genetics, body size, body composition, exercise habits, and environmental conditions

DRI reccs for water in (AI)

• men

• woman

• Adequate intake (AI) in men 3.7 L/day (16 cups per day)

• Adequate intake (AI) in women 2.7 L/day (12 cups per day)

what is important to note regarding fluid intake 

these values can be met from a variety of foods and fluids (not just fluid)

for athletes, guidelines for fluid before exercise?

5-7 ml/kg 2-4 hours before execise

fluid intake during exercise depends on

sweat rate

general guideline for fluids during exercise

0.4-0.8 L/h

guidelines recommend ingestion of what with water 

sodium (to reduce sweat losses) 

after exercise guidelines?

1.25-1.5 L fluid for every 1 kg lost during exercise

fluid intake during exercise has the goal to **

limit dehydration to 2% of body mass

after exercise, you want to replace fluid losses by (%) if dehydration is severe/rapid hydration needed

120-150% of body mass loss

beneficial response to adequate fluid intake durig intake (4)

1. ↓ Heart rate

2. ↑ stroke volume and cardiac output

3. ↑ skin blood flow and ↓ core temperature

4. ↑↑↑ performance

benefits for fluid intake during exercise are seen when

dehydration is minimized

minimal dehydration is defined as

<2% decrease in body weight

fluid intake choices 4 hours prior to exercise?

Gatorade, Powerade, water, fruit juice

when may coffee serve as good pre-exercise fluid 

1 hr before (studies show a bit of caffeine can improve performance)

what can be used to determine hydration status prior to exercise/ start of exercise (2)

urine color OR urine specific gravity test

athletes should have _____________ fluid intake plans

customized

simple approach for fluid needs is to do what?

record body weight before and after exercise

weight loss means (in terms of fluid needs)

inadequate drinking 

weight gain means (in terms of fluid needs)

excessive drinking 

advanced approach for fluid needs involved what 3 things

make calculations based on weight, fluid intake, urine output

calculating fluid needs math

Charlotte cycles for 3 hours in Houston in summer. Her pre-exercise body weight is 65 kg and her post-exercise body weight is 63 kg. She drank 500 ml of fluids during her ride and did not go to the bathroom. What was her hourly sweat rate?

1. ∆ body weight = 65 kg − 63 kg = 2 kg

2. 2,000 g + 500 ml of fluids = 2,500 ml of sweat lost during the ride

3. 2,500 ml / 3 hours = 833 ml per hour or 13.9 ml/min

during exercise drinks (for most athletes)

Powerade, Gatorade, water is just fine (90% of time)

when exercise is >2.5 hrs, what drinks can be useful

60-90g of multiple transporter carbs containing fluid

symptoms of dehydration?

• Increased thirst and presence of dry mouth

• Little or no urine output

• Dark, concentrated urine

• Fatigue, confusion, headaches

• Muscle cramps

• Chills → can be a sign of heat stroke

post exercise, we want to replenish fluid losses to how much 

120-150% 

post exercise fluid needs math

post exercise fluid choices

water, Gatorade, Powerade, milk

why is milk a good post exercise fluid?

contains protein, fat, and electrolytes

what are electrolytes ** (what minerals) 

sodium, chloride, potassium, calcium and magnesium

functions of electrolytes (4)

regulating fluids in the blood plasma, blood pH, enabling muscle contractions, nerve conduction

sweating effects which electrolytes

sodium and chloride (rest is minimal loss)

electrolyte loss due to sweating can lead to what?

severe muscle cramping and hyponatremia

what is hyponatremia

Low sodium levels in the blood (< 135 mEg/L)

symptoms of hyponatremia

Fatigue, headache, confusion, nausea + vomiting, muscle cramps and spasms

hyponatremia has similar symtoms to what?

dehydration (which makes it hard to know / detect)

what causes hyponatremia in athletes?

Syndrome of inappropriate anti-diuretic hormone (SIADH) (high levels of ADH) combined with intake of too much water or fluids

what general things cause hyponatremia 

 medications (diuretics), severe diarrhea or vomiting

athlete-related risk factors for hyponatremia include (6)

• Excessive drinking

• Weight gain during exercise

• Low body weight

• Female sex

• Slow running pace

• Inexperienced runners

event related risk factors for hyponatremia include (4)

• High availability of drinking fluids

• > 4 hour exercise duration

• Unusually hot conditions

• Extreme cold temperatures

what is recommended for athletes at risk for hyponatremia (before exercise)

do not overconsume fluids 

what is recommended for athletes at risk for hyponatremia (during exercise)

 Drink to thirst. Beverages containing sodium at aid stations

what is recommended for athletes at risk for hyponatremia (after exercise)

Hypertonic saline solutions to ↓ risk of symptomatic hyponatremia following exercise

what should be a focus post exercise to reduce risk of hyponatremia?

electrolyte replacement sources —> food and beverages containing sodium

for marathon races in hot climates, what is recommended pre, during, and after race?

1. Pre-race nutrition and hydration should be optimal

2. Probably need 0.8 – 1.0 L/hour of fluids during the race with additional sodium

3. 60 – 90 g of CHO per hour in the form of single and multiple transportable CHOs

what is key when exercise will take place in a hot climate that athlete is not used to?

heat acclimation

heat acclimation will require how many days of training in that environment

7-14 days