Hydration is a very important aspect of sports performance– when athletes are dehydrated, their sports performance suffers. And why is it that some athletes still experience dehydration, heat cramps, heat exhaustion, and heat stroke? It can’t be due to lack of availability of water, as water is free and readily available in the US. What it could be due to, is a lack of education on the importance of staying properly hydrated.
For my internship rotation this week, I got to pick a sports nutrition topic to speak to a sports team about, and I chose hydration. I spoke to about 40 athletes on the swimming team, and Roanna covered pre-workout snacks as well as breakfast for these swimmers who have 5:30am practice. Here are the key points from my speech on hydration.
What’s the big deal with water? Water is arguably the most important nutrient for athletes, and it’s not even a nutrient that provides any energy, or calories. The human body is generally 55-60% water, and your muscles are about 70% water. So any large fluctuations in body water storage can lead to a variety of health concerns as well as poor sports performance. Urine output typically contributes to 60% of water loss, with the remainder through sweat, waste, and respiration. However during exercise, sweating can contribute up to 90% of water loss. This amount depends on body size, exercise intensity & duration, and the physical environment. The only way to maintain hydration status on a daily basis is to make sure your daily water intake is equal to your daily water loss. The goal is for water balance.
What are the consequences of poor water balance? Failing to maintain that water balance can have negative effects on health and sports performance. When there is a net loss of body water, it can lead to increases in body temperature which in turn can lead to heat cramps, heat exhaustion, and heat stroke. Dehydration also leads to a loss in blood volume. When there is decreased blood volume, the heart is pumping less blood to the muscles, which means that muscles are getting less oxygen delivered to them. This basically means the muscles are unable to work as hard. Secondly, when the aerobic capabilities of the muscles are diminished, the muscles begin to rely more heavily on anaerobic metabolism. The more the body has to rely on anaerobic metabolism, the quicker lactic acid builds up in the muscles, the higher the perceived rate of exertion, and the faster fatigue will set on. All of this can lead to less than optimal sports performance!
As little as a 2-3% decrease in body weight caused by dehydration (150# athlete losing 3-4.5# body water during exercise) can result in those increases in body temperature and heart rate even though the intensity level of the exercise remains the same. Symptoms of a 2-3% decrease in body weight due to dehydration include: increased thirst, loss of appetite, discomfort, increased heart rate, impatience, and decreased blood volume.
How much fluid do individuals need on a daily basis? The adequate intake for fluid for males (ages 19+) is 3.7 liters per day and for females, 2.7 liters per day. However these numbers include the fluid that we consume through solid food intake, such as fruits and vegetables. Therefore the adequate intake for fluid/beverage intake is 3.0 liters(13 cups) per day for males and 2.2 liters (9 cups) per day for females. Athletes may to need switch around and modify these recommendations based on their activity levels and the physical environment around them. Another way to determine your daily fluid needs would be to drink 1 mL of fluid per 1 calorie consumed. So an athlete on a 2000 calorie/day diet would need to consume 2000 mL or 2 L (8.33 cups) per day.
On a daily basis, the goals would be to drink enough water to produce clear or pale yellow urine. Optimal hydration is going to stimulate urine every couple of hours. And caffeinated beverages can be included in fluid intake, but keep in mind that caffeine has a slight diuretic effect. For every 1 mg of caffeine, there is a 1 mL fluid loss. So if someone has a 240 mL cup of coffee, that contains 80 mg of caffeine. Meaning 80 mL of that 240 mL is going to be lost through that diuretic, transient effect. So a 240 mL cup of coffee really only provides about 160 mL of fluid gain.
What is the role of pre-exercise hydration? The goal of hydration before exercise is to really set the stage for optimal sports performance. Athletes who avoid fluids before training or competition tend to fatigue quickly, experience dizziness or fainting, have increased body temperature, increased heart rate and perceived level of exertion, and consequently perform at a sub-optimal level. However, athletes probably don’t want to over-hydrate either, as frequent bathroom breaks can disturb practice time (keep in mind though, that slight over-hydration is better than slight dehydration, performance-wise). The recommendation is to consume generous amounts of water 24 hours before the event/training. Be well hydrated the day before! Then, about 4 hours before exercise, drink 13-20 oz. If the urine remains darker than that pale yellow or clear color, drink about 8-13 oz 2 hours before exercise. Then, 10-20 minutes before exercise, drink 7-10 oz. It’s best to stick to water rather than sports drinks at this point, because sports drinks are really designed as a fluid replacement to be used during practices– save the Gatorade for after a long practice.
What is the role of hydration during exercise? The goal of hydration during exercise is to maintain plasma volume and electrolyte balance for optimal sports performance. The fluid and electrolytes lost during exercise can vary greatly from individual to individual. It all depends on body size, exercise intensity, exercise duration, and physical environment (temperature, humidity, wind velocity). For some, fluid losses may be no more than 16-20 oz per hour. For others with more intense workouts in warmer and more humid climates, fluid losses may be closer to 2-3 L per hour.
For short-duration activities, your normal intake of electrolytes may be adequate to replenish losses in sweat. That is, if all you’re doing at a track meet is 3 attempts at a high jump, water will work just fine. For athletes competing and training for longer durations (>45 minutes) at higher intensities (say, a 10k race), electrolyte replacements via sports drinks will be critical for sports performance and to prevent low sodium in the blood.
Athletes should aim for matching their sweat and urine output (fluid losses) with fluid consumption. The goal is to maintain hydration at less than a 2% reduction in body weight. Now, unless an athlete is weighing themselves religiously before, during, and after every practice, how will they know if they’ve lost 2% of their body weight in water? In addition to paying attention to the signs and symptoms of dehydration, athletes should know that for most individuals, 7-10 oz of water every 10-20 minutes during exercise should provide adequate hydration during exercise. Aiming for an 8 oz cup of water every 15 minutes is a good goal to have. If an athlete is using sports drinks during prolonged exercise (ie: 60-90 minutes), keep in mind that beverages should be no more than 8% carbohydrate solution. If an athlete drinks a fluid containing more than 8% carbohydrate solution, it will pull water into the intestines and can cause bloating, cramps, and diarrhea. How do you figure out the % carb solution? Take a look at the nutrition facts. Take the grams of carbs per 8-oz serving, and divide by 240 mL. Multiply by 100 to get the percent carbs. For example, a sports drink that contains 15 grams of carbs per 8 oz (240 mL) serving would be a 6.25% carbohydrate solution. An 8% solution would have no more than 19.2g of carbs per 8 oz serving. Fruit juice is typically around 15%! If you want a fruit juice, try watering it down to get to that 8%.
So things to remember during exercise: know where the fluid is; it should be readily available. Bring a water bottle, know where the beverage station is, or be aware of where water fountains are. Consume fluids early in practice. It’s going to take about 10-20 minutes for any water ingested to reach the blood stream, so fluid should be consumed continuously and gradually during practice and competitions rather than all 32 oz at once. Additionally, sports drinks are not necessary unless the exercise session lasts longer than 60-90 minutes. These longer duration exercises need carbohydrate and electrolyte replacements, but for shorter duration exercises, plain water is recommended.
What is the role of post-exercise hydration? After exercise, water plays an important role in speeding up the recovery process. Athletes should replace water lost as soon as possible, within 2 hours. Drinking slowly and consistently is recommended, and urine should return to that pale yellow/clear color. If you did weigh yourself before you exercised, your weight after exercising should be within 1% of your original, pre-exercise body weight. That means for a 150# athlete, they should weigh no less than 148.5# after rehydrating. The rule of thumb is to drink 2-3 cups (16-24 oz) of fluid for each pound lost during exercise. And again, for long-duration (60-90 minute) physical activities, sports drinks afterwards will provide the electrolytes that were lost from sweating, as well as speed up the replenishing of fluid and energy reserves.
*Remember* Hydration Training! Get into a hydration routine during training and practices. If you all of a sudden amp up your fluid intake during a competition, it could cause gastrointestinal distress because that level of hydration is unfamiliar to your body. If you get into a proper routine now, they’ll be no surprises during competitions…just excellent performance.
Source: Practical Applications in Sports Nutrition, 3rd Ed., by Fink, Mikesky, & Burgoon
Emily Todhunter, WVU Graduate Dietetic Intern 