Hydration and Sports Drinks Heat Removal • Exercise increases core temperature. For every L of O2 consumed during exercise ~5 kcal is produced but only 1kcal is used for mechanical work – the rest is heat • Increases in core temperature: – Increase blood flow to the skin – Initiate sweating Sweating and Fluid Loss • Mild to moderate work and routine physical training typically result in whole-body sweat losses of about ~0.8-1.4 L/h. • Evaporation of 1L of water from the skin will remove 573 kcal of heat from the body. • Heat loss via evaporation of sweat is largely dependent on the humidity (proximate to the skin) in which the athlete is working. • Individual sweat rates and fluid losses vary widely between athletes and across sports. Dehydration and Performance • If sweating is not compensated for with fluid intake performance is affected. – Dehydration may explain some of the fatigue at the end of a long sporting event. • Exercise performance is impaired by a fluid loss of 2% (this is 1.5L in a 155lb male athlete), Losses in excess of 5% can decrease work capacity by 30% (water weight loss of ~8lbs) In cool laboratory conditions, VO2max has been shown to decrease with fluid losses > 2% BW... In the heat, sweat rates increase even more such that fluid intake must be even more closely monitored. Exercise Capacity 100% 80% 60% 0 1 2 3 Body weight loss (%) 4 5 How does sweating (fluid loss) work to decrease performance? increase in plasma osmolarity (higher concentration of solute in solution) release of vasopressin (ADH) from the posterior pituitary gland. ADH causes the kidney to re-absorb water Urine volume goes DOWN dramatically to preserve blood osmolarity, volume and pressure As exercise progresses, the transfer of body water into the plasma cannot keep up with sweat losses so...performance decreases. How can I tell how much I’m sweating? Pre exercise weight Post-exercise weight Volume of fluid consumed during exercise Exercise duration 55 kg 53.5 kg 1 kg 2h Calculations • Fluid deficit (L) = 55 kg – 53.5kg = 1.5 kg • Total sweat loss (L) = 1.5 kg + 1 kg = 2.5 kg • Sweat rate (L/h) = 2.5 kg / 2hr = 1.25 L/h Hydration & Rehydration 1 2 3 4 5 6 7 8 • Urine Color Chart • Assess Hydration • 1, 2, or 3: Well Hydrated • 7 or Darker: Dehydrated Daily Water Balance Athletes need to be fully hydrated before training/competition The average sedentary person excretes about 2700 milliliters of water/day (1400 from urine, 1100 sweat/breath) To replace that 2700 ml, get: • 300-400 ml from metabolism, • 1000 ml from food and • 1300-1400 ml from beverages 2700 ml Athletes and Daily Water Balance Athletes and Fluid Intake • Athletes have to consider their daily water balance and sweat loss during exercise when they construct a hydration plan. – Choices to maintain/increase fluid intake: • • • • Water CHO drinks Choc Milk Coca-Cola • The maximum amount of fluid that empties from the stomach during exercise is ~0.81.2 L/h. – Remember, sweating during exercise can cause fluid losses of 0.8-1.4l/hr • Up to 10% CHO solution empties from the stomach at the same rate as pure water (Coke is 11%) • Glucose and sodium both stimulate the absorption of fluid across the membrane of the small intestine. • Athletes should consume enough water throughout exercise that their weight remains constant (if possible) • Guidelines for fluid intake are VERY general due to the variability of sweat rates among individuals. – Good rule of thumb is to consume something every fifteen minutes (8-12 oz.) Before ACSM NATA AIS Gatorade NCAA 500 ml : 2 hours 500-600 ml : 2-3 hours Ind 17 - 20 oz : 2 to 3 hours 17 - 18 oz : 2 hours 200-300 ml : 10-20 min 7-10 oz : 10 - 15 pre warm-up Regular Intervals 200-300 every 10-20 min Ind 7-10 oz every 10-15 min 8 oz every 10-15 min After Equal to loss 150% of weight lost Ind 20-24 oz / lb 20-24 oz / lb Temp 59o - 72o F 50o - 59o F Ind Cooled 50o - 59o F CHO and Sodium CHO and Electrolytres Ind CHO (6-7%) and Sodium - During Contents After Exercise • Drink 150% of water weight loss to achieve normal hydration 6hrs post-exercise (this accounts for reduced urine output) • Pure water may not be the ideal recovery drink: – Causes rapid fall in plasma sodium and thus plasma osmolarity which reduce the stimulation to drink and also increases urine output. This can delay the rehydration process • What to drink then? – Plasma volume is rapidly restored if some sodium chloride is added (77mol or 0.45g/L) Sodium: – Helps maintain thirst, delays urine production Potassium: – Thought to promote intracellular hydration (little evidence to support this, but it sounds good) CHO (glucose, glucose polymers) – More likely to continue drinking fluid if beverage is sweetened (taste) vs. pure water – Presence of glucose stimulates fluid absorption – We know it helps with muscle glycogen re-synthesis CHO Sports Drinks • The goal of the carbohydrate content is to provide the appropriate CHO concentration while preventing gastrointestinal disturbances. – At 6-8% carbohydrate concentration, sports drinks have can be absorbed 30% faster than water. • The composition of the carbohydrates in sports drinks is another variable that affects the effectiveness of the drink The 3 things a sports drink should accomplish: • Hydrate effectively. • Replenish electrolytes. • Provide energy for working muscles to enhance performance and speed recovery. Gatorade • Gatorade – 6% Carbohydrateelectrolyte solution. – 14 g of CHO (sugar) in 8 fl oz. – 110 mg of Na+ in 8 fl oz. – 30 mg of K+ in 8 fl oz. – 90 mg of Cl- in 8 fl oz. – Retail Price $1-2. Powerade • PowerAde – 7% Carbohydrateelectrolyte drink. – 18 g of CHO in 8 fl oz with 15 g as sugar. – 53 mg of Na+ in 8 fl oz. – 34 mg of K+ in 8 fl oz. – Retail Price $1-2. Flavored Water • Propel Fitness Water – – – – – – – – – – Calories 10 in 8 fl oz. Sodium 35 mg Potassium 40 mg Total Carbohydrate 3 g Sugars 2g Vitamin C 10% Vitamin E 10% Niacin 25% Pantothenic Acid 25% Vitamin B12 4% Vitamin B6 Retail Price $1.25 per bottle. • From the textbook to the track: – Don’t wait until thirsty... Thirst signal is the result of being slightly dehydrated. – Monitor urine output and weight before and after exercise (approximate fluid loss) – In hot weather athletes need to consume more fluid during/after exercise compared to colder weather. – For recovery, supplement with a carbohydrate drink that contains some sodium to aid in replenishment of glycogen stores and electrolytes. (remember the protein)... Gatorade, Choc milk or coke?