Water Balance and Exercise Performance NFSC 303 Nutrition and Fitness

“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 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 w/ 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 Dehydration Mild 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

– – 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: – – – –