At the end of this unit, you will understand the importance of hydration for athletes and be able to provide general and specific recommendations for fluid intake as it relates to level and type of physical activity.
Other than climate factors, the amount of body water lost through sweat can also be affected by these other factors shown on the slide. When working with athletes you need to consider these factors when making fluid recommendations.
When we sweat as a result of vigorous training the response is a lower blood volume and a higher blood concentration of some nutrients. The kidneys respond by decreasing urine output, and retaining water and sodium. This makes the athlete feel thirsty, raises body temperature, and increases heart rate.
Shown here is the sequence of events that lead to poor physical performance as a result of dehydration or low blood volume.
Sodium is the electrolyte lost in greatest amount through sweat. Some chlorine is lost along with it. There are very small losses of potassium and even smaller losses of calcium in sweat.
Athletes should aim to replace fluid losses within 24 hours. This allows the athlete to start the next training session fully hydrated. General guideline to assure hydration at the start of training are to drink 2-3 cups of fluids 2-3 hours before training. This allow time for fluid to absorb and any extra to be excreted. Then drink another 8 – 12 ounces just before activity.
Sports drinks can also be taken before activity but are really intended for during activity. Some athletes will use caffeinated drinks as a physical performance booster. But too much caffeine can backfire. I personally prefer a dopio espresso before a long ride.Drinking soda is a somewhat common practice among athletes for hydration but it is not recommended. The fizz can cause discomfort, sugar concentration can cause GI issues, and it does not entice athletes to drink adequate amounts of fluid.
Hydration during exercise replaces lost water & and electrolytes. The hotter the temperature and higher humidity, the more fluid will be needed. Athletes who may train in one climate but compete in another will need recommendations from you for both conditions.
To personalize hydration recommendations, you can calculate a sweat rate. Take the athletes weight before and after training. Multiply this by 16 ounces to convert the weight into oz. Then add any amount of fluid in ounces that the athlete consumed during training. This tells you the total amount of fluid lost. In the example shown, the athlete has 2 pound change in weight but drank 16 oz. during the training. Had the athlete not drank anything during training, they would have shown a 3 pound loss. So 2 pounds would be equal to 4 cups or 32 ounce plus the ounces the athlete drank would be 48 oz in 2 hours. The athletes sweat rate is then 24 oz per hour to prevent a decrease in body weight during training. This can further be broken down to 8 oz every 20 minutes. In this case a 24 oz re-usable sports bottle will work great. Athletes do not want to count ounces all the time so if they know they should aim to drink one bottle in one hour, it makes it easier to comply. You can also tell them to count gulps. One gulp is about 1 oz.
Another reason for telling athletes to gulp or take in about 8 oz at a time is to increase gastric emptying. The higher the volume, the faster the emptying and less sloshing around. Also CHO in a sports drink helps with emptying and absorption. A full stomach will slow the athlete down.Sweat rates may change as the athlete becomes better trained or acclimatized to training conditions. After about 2 weeks you should re-evaluate.
To determine the CHO concentration of any beverage, use this formula = grams of CHO per cup divided by 240 ml. Then multiply by 100 to get a %.
When choosing a sports drink, these are some things you may want to avoid or risk serious GI distress.
In summary, hydration is a key factor in sports performance and essential for maintaining normal blood volume. The type of fluid an athlete should drink will depend mainly on length of training or competitive event and climate conditions. As the sports RD you can calculate the athletes sweat rate in order to provide individualized guidance and encourage the athlete to monitor their own hydration using urine color as an indicator. Lastly for each pound lost during training, 2-3 cups of fluid is needed for rehydration.
Fluids and Sodium Lecture
FLUIDS: WHAT & HOW MUCH TODRINK? Lona Sandon, M.Ed., R.D., L.D. Assistant Professor
OBJECTIVES Discuss the importance of hydration Explain the consequences of dehydration Differentiate dehydration and hyponatremia Estimate fluid requirements of athletes Make recommendations for meeting fluid needs Discuss the importance of hydration before, during, and after exercise
WATER Arguably the most essential nutrient Restriction can lead to death in days Just 1-2% slight dehydration decreases training performance
BODY WATER Makes up ~60% of body weight Types of body water Intracellular(inside cells) – 2/3rds of body water Extracellular (outside cells) One-thirdof body water Lymph, blood plasma, etc. Muscle tissue holds more water than fat tissue Lean athletes likely to hold more H2O
FUNCTIONS OF WATER Provides cell structure Delivers nutrients & removes waste Medium for chemical reactions Cools the body Brings water to the surface of the skin - sweat evaporation
FUNCTIONS OF WATER Major component of blood volume 3-5% dehydration inhibits cardiovascular function Helps balance pH & buffer effects of lactic acid from intense exercise Hemoglobin Sodium bicarbonate
SOURCES OF WATER ~ 60-80% from beverages Milk, sports drinks, juices, other beverages Caffeinated drinks can count Bottled water < 30% from foods Fruits, vegetables 10% from H2O formed during metabolism of macronutrients
HOW IS BODY WATER LOST? Urination loss during rest Up to 60% losses Sweating during exercise Up to 90% of losses Some athletes can lose 1-2 L/hour Feces Insensible perspiration Breathing Drier air = more H2O loss Training in high altitude increases water loss
FACTORS AFFECTING SWEAT LOSSES Temperature Humidity Wind velocity Intensity of exercise Duration of exercise Size of athlete – smaller athletes typically lose less sweat due to body surface area
SWEAT LOSSES RESULT IN: Decrease in blood volume Increased plasma osmolality Decreased urine output Increase water & sodium retention via renin- angiotensin system Stimulates thirst Increased core body temperature Increased heart rate
WATER BALANCEWater intake < Water Loss DehydrationWater intake = Water Loss BalanceWater intake > Water Loss Hyperhydration Water balance is normally regulated quite well in most people within 0.2% of total body weight on a day to day basis. Many experts argue that carrying around water bottles all day long is really quite silly. Drinking with meals is sufficient for most. However, sweat losses can derail this delicate balancing act.
DEHYDRATION AFFECTS PERFORMANCE Low blood volume Less blood going to working muscles Impaired muscle work Less oxygen delivery Reliance on anaerobic metabolism Lactic acid build- ’d perceived exertion Fatigue up Poor performance
HYPONATREMIA/H2O INTOXICATION Rare condition, associated with over- hydration Defined as blood sodium concentrations <130-135 mmol/L Na+ becomes critical after 3-4 hours of exercise The untrained & those acclimatizing to heat have greater fluid & Na+ losses
HYPONATREMIA/H2O INTOXICATION Caused by: Hyperhydration prior to exercise Athletes following a low salt or salt free diet Consuming fluid amounts greater than sweat rate Drinking only water during long duration exercise Exercising more than 4 hours Diuretic medications for hypertension Use of NSAID medications before or during exercise High sodium and chloride losses in heavy sweaters Most common in endurance & ultra-endurance events, and small females
HYPONATREMIA Sign & symptoms Intoxicated like actions Muscle weakness Poor muscle coordination Disorientation Seizure & coma if severe & not treated Prevention Drink sodium containing rehydration beverages (i.e. Gatorade) Eat salty snacks before or during exercise High salt losers may need to salt their foods
MONITORING HYDRATION LEVEL Monitor body weight changes Weigh pre- and post-workout Weigh at same time of day, ideally morning weights Consume 2 to 3 cups of fluid per pound lost during training Monitor urine color Pale lemonade = good hydration Dark, strong smell = dehydration Can be effected by multivitamin supplement Urine frequency ~ every 2 hours while awake
HYDRATION LEVEL AND URINECOLOR Should not go below this level, minim al dehydration.
RECOMMENDATIONS FOR DAILY FLUID INTAKE Adequate Intake (AI) for adults > 19 years Females – 2.7 L/d (~12 cups fluid) Males – 3.7 L/d (~16 cups fluid) 1 ml/kcal consumed Ex: 2000 kcal/d = 2000 ml or 8.33 cups fluid per day Athletes eat more kcals & therefore need more fluid Estimate daily fluid needs based on calorie intake Add 2-3 cups per pound weight loss during training
TIPS FOR ATHLETES ON HYDRATION Calculate individual Consume caffeinated needs. drinks in moderation. Ideal hydration leads Don’t overdo protein to urination every 1 to consumption. 2 hours. Be conscious of the Maintain pale urine. effects of medications Get daily fluids from a on hydration levels. variety of sources, not Avoid alcohol. just water.
FACTORS AFFECTING HYDRATIONNEEDS Know the conditions the athlete is training under: Environmental temperature Acclimatization to heat of athlete Altitude Fitness level of athlete Body size Age Activity level Sweat losses
ELECTROLYTE LOSSES Na+ lost in greatest amounts in sweat lose ~1 000 mg/L of sweat (~1/2 tsp) Cl- lost with it Highly variable among individuals High losses associated with increased risk of muscle cramping, hyponatremia, heart problems Physically active people need higher NaCl intakes above the DRI recommendations K+ loss is very small Despite popular belief, K+ loss does not cause muscle cramping K+ – lose 76 – 152 mg/L of sweat (mild loss) Some Ca++ loss in sweat
PRE-EXERCISE HYDRATION 24 hours prior Meet estimated fluid needs 2 to 3 hours prior to training Drink ~2 to 3 cups fluid 10 to 20 minutes prior Drink ~1 – 1 ½ cups fluid
PRE-EXERCISE HYDRATION: WHAT TYPE? Best Choices Water Juices Provide vitamins, minerals, CHO, elect rolytes Test tolerability Milk Provides Ca, vitamin D, CHO, PRO, electrol ytes Test tolerability
PRE-EXERCISE HYDRATION: WHAT TYPE? Sports drinks Provides CHO, electrolytes Intended for during activity Caffeinated drinks Ergogenic May cause shakiness, GI distress Test tolerance Soda’s Not recommended Non-nutritional value Bloating from carbonation Do not encourage athletes to drink enough
HYDRATION DURING EXERCISE Purpose: Maintain blood volume Maintain electrolytes Maintain sweating for cooling 2-3% body water loss affects performance Thirst is not a good guide – indicates mild dehydration, too late Recommend 7-10 oz. every 10 to 20 minutes
HYDRATION DURING EXERCISE Replace H2O losses Moderate temps - ~2 – 2 ½ cups/hr (16-20 oz.) Hot, humid temps – up to 2 -3 L/hr Electrolyte replacement critical for: Long duration & high intensity training lasting more than 60 min. Hot, humid conditions, prevent hyponatremia
HYDRATION DURING EXERCISE Calculate sweat rate (#’s before exercise - # after exercise) x 16 oz. 1# = 2 cups of water loss Add oz. of any fluid consumed during exerciseEx: 150# pre-workout, 148# post-workout, drank 16 oz. over 2 hours of exercise [(150-148)x 16] + 16 = 48 oz. or 6 cups fluid loss/2 hrs Needs 3 cups/hour or 8 oz every 20 min. during exercise
HYDRATION DURING EXERCISE Volume & gastric emptying CHO enhances emptying & absorption Higher fluid volume stimulates emptying Tell athletes to gulp not sip – 1 gulp = ~1oz. Acclimatization Initial increase in fluid needs first 10-14 days training in higher temperatures Reassess after 2 weeks Altitude Increases dehydration risk, drier air, increased breathing rate
WHAT TO DRINK DURING EXERCISE? Adequacy of intake affected by: Temperature of fluid– colder usually better Palatability – must like it Digestibility Na+ & sweet (CHO) taste increase palatability & encourages athletes to drink more & adequately replace fluid losses Water only shuts off thirst mechanism before adequate fluid replacement
WHAT TO DRINK DURING EXERCISE? Water Good for short duration, moderate temperatures Sport beverages: - Recommend for practice or event lasting longer than 60 to 90 minutes
WHAT TO DRINK DURING EXERCISE? Benefits of sports drinks Provides needed easily digestible CHO, 1 L = 60-70 g CHO 6–8% CHO mix enhances gastric emptying & absorption Sweet taste gets athletes to drink more Provides electrolytes, mainly Na+ which drives the desire to drink & increases palatability Electrolyte deficiency leads to: Musclecramping Hyponatremia
% CHO CONCENTRATION Ex: 14 g of CHO per 8 oz. serving (240 ml) (14 g/240 ml) x 100 = 5.8%
WHAT TO AVOID IN A SPORTS DRINK Glucose polymers or fructose as the only CHO sources Artificial sweeteners – surgar alcohols Stimulants – caffeine, guarana, kola nut High amounts of vitamins/minerals Carbonation Juice – too concentrated High osmolality leads to GI distress
PRACTICAL GUIDELINES FORHYDRATION Fluids should be readily available. Fluids being consumed should be based on personal preference for taste. Regular and frequent breaks should be allowed. Start ingesting fluids early during exercise before getting thirsty. Drink cool fluids (50–59oF) rather than warm ones. Have athletes practice staying hydrated during training not just during competition.
POST-EXERCISE HYDRATION Begin rehydrating as soon as possible. Drinks and foods containing carbohydrates and sodium are good choices. Plan ahead and have drinks readily available. Avoid drinking large quantities of water in a short time, rapidly excreted. Drink 2 to 3 cups of fluid for every pound lost.
POST-EXERCISE HYDRATION Purpose: Replace fluid & electrolyte losses Replace CHO for muscle glycogen repletion & PRO for repair Types of fluids: Flavored milk, vegetable juices, sports drinks, soups, water with food Recovery beverages/supplements Consider Kcal, CHO, electrolytes, & excess vitamins/minerals Cost? Chocolate milk has been shown to work just as good or better than most products
SUMMARY Hydration impacts performance Water is good for moderate, 60 min exercise Sports drinks are needed for endurance events/tournament style intermittent sports >60- 90 & in hot, humid climates Athletes should know their sweat rate Athletes can self-monitor hydration status 2-3 cups needed for each pound lost Goal of hydration is to maintain blood volume & electrolyte balance
REFERENCESAmerican College of Sports Medicine. Exercise and fluid replacement. Medicine & Science in Sports & Exercise. 2007,9:377-390.Fink HH, Burgoon LA, Mikesky AE, eds. Practical Applications in Sports Nutrition. Sudbury, MA: Jones and Bartlett; 2006Murray B. Fluid, electrolytes, and exercise. In: Dunford M, ed. Sports Nutrition: A Practice Manual for Professionals, 4th ed. American Dietetic Association; 2006.