Water Balance and Exercise Performance

Developed By: AQ Khan

“While it is possible to live for several weeks or even months without food, our bodies can feel the effects of water deprivation within as little as 30 minutes.”

Water Balance

Water comprises 60-70% of body weight

• Gives structure to cells• Body Fluids:

– saliva, blood, digestive juices, etc.• Solvent for nutrients and waste products;

transport of these• Padding/lubrication:

– joints, spinal cord, GI tract• Thermoregulation

• Intracellular water (~2/3)– inside cells

• Extracellular water (~1/3)– interstitial (between and around cells)– in blood

Water weight varies with body composition:

• 1g protein (lean tissue) is associated with • 3g water• 1g glycogen – • 1g fat –

So lower body fat and higher muscle/glycogen

•Low kcal/low CHO diet • decreased glycogen stores (metabolized for

energy)

• decreased body protein (metabolized for energy or gluconeogenesis)

• weight loss from decreased body water

Water Balance• Water “in”

– water in food, beverages, and water produced during metabolism of food

• Water “out” – skin, urine, feces, lungs

During heavy exercise: losses up to 4 lb/hour possible

Thermoregulation is affected after:

Electrolytes• Charged atoms (ions) that conduct electrical current• Involved with fluid balance:

– Sodium (Na+) extracellular fluid– Potassium (K+) intracellular fluid: important in:

• the generation of electrical impulses to nerves• muscle contraction• transport of glucose into the muscle cells • glycogen storage

Electrolytes

• Chloride (Cl-) major negative ion in both body fluids and in foods.

• Works w/Na+ in the regulation of both acid-base balance and fluid balance.

Water dissolves salts and follows electrolytes

Regulation of Body Water

• Osmotic pressure:– membrane with solution on either side (intra- and

extracellular water)– Water can pass through freely, but not solutes– The concentration differs according to the # of

particles per unit volume– Water is drawn from the compartment with low

concentration to the one w/ high concentration

Factors affecting water balance

• Diuretic: substance that causes the body to excrete water– – –

Factors Affecting Water Balance• ADH: Anti-diuretic Hormone

– Secreted when blood concentration of ions rises–

• Thirst:

RDA for Water

• 1 ml/ kcalorie expended– (your kcals = your ml water recommended via

food and liquids)

Thermoregulation

• Water absorbs heat from muscles blood to skin blood cooled by evaporation of sweat.– humidity: less evaporation of sweat/higher body

temp.– hot, dry climate: more sweat/water loss

• Excessive body temperature: – nausea, dizziness, cramps (heat exhaustion)– can heat stroke (can be fatal)

Exercise and Water Balance• During exercise: water lost through breathing and

sweat• Effects of a 1% body weight water loss:

– – – – – risk of injury

Signs of DehydrationMild Dehydration

• Thirst• Sudden wt. Loss• Dry mouth, throat,

body linings• Rapid pulse B.P.• Weakness• Dark, infrequent

urination

Severe Dehydration• Pale skin• Bluish lips and

fingertips• Confusion• Rapid, shallow

breathing• Weak, rapid, irregular

pulse• Shock; seizures• Coma; death

• During exercise, sodium and chloride are lost in sweat

• But, kidneys respond by reabsorbing more Na+ and Cl-

• Unnecessary to supplement in most cases (too much K+ can be dangerous)

• Losses of Na, K, calcium magnesium and phosphorus are easily replaced in the diet

• Sports drinks supply electrolytes in the event of heavy losses

Preventing dehydration:

• Consume adequate fluids daily– clear urine every 2-4 hours– dark colored, infrequent urination indicates

dehydration

Preventing dehydration: • Before exercise:

– 7ml/kg (~1 oz/10lb) water or sports drink about 2 hours before exercise

• More for profuse sweaters: weigh pre- and post- training session

– kidneys need 90 min to process fluids– then 1-2 cups a few minutes prior to exercise– cold beverages are absorbed more quickly

• During exercise– Don’t rely on thirst alone (mechanism blunted during

ex)– Drink early and regularly– Fluid replacement enhances performance

–

– 1 - 1.5 cups fluid every 15 to 20 minutes during endurance activity to keep gastric emptying up.

Sports Drink

• contain CHO to help maintain glycogen• more than 8-10% CHO

– water drawn osmotically into the intestine – bloating, cramping, and diarrhea (osmosis)

Sports Drink

• 6-8% CHO solution is best (most sports drinks)– encourages more consumption and is

absorbed quickly (12-20g CHO/cup)– fruit juice diluted 1:2 with water

• Glucose polymers in sports drinks are quickly absorbed

• Exercise >60 min, CHO drinks enhance endurance

After exercise:– CHO repletion after exercise to replete glycogen:

1g/Kg within first 2 hours, then high CHO diet thereafter (65-70%)

– Post exercise fluids should be high glycemic index fluids (low fructose)

– Protein-CHO combination may increase glycogen re-synthesis (3g CHO:1g prot)

– Salt supplement tablets are not generally recommended (gastric irritation and excess fluid retention)

Acclimatization

• Exercising in a different climate over 5-10 days – –

• Regular exercise also produces acclimatization-type effects:–

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