Hydration: What You Need to Know

– From the Desk of Ready’s Chief Science Officer, Kim Beals –

Chances are, you may be one of the 75% of youth athletes (8-18 years) who show up to practice in a dehydrated state and not even know it.  Chances are, you do know that dehydration or a reduction in the amount of water in the body, may have a negative effect on sport performance and health.  The best way to improve your hydration status is to develop a personalized hydration plan.  Keep reading to see how to customize your hydration plan!

How Does Hydration Effect Athletic Performance? 

Water typically accounts for approximately 60% of the body mass and plays an important role in maintaining body temperature and delivering important nutrients to muscles during exercise.

Hydration status is determined by the balance between water intake and water loss.  Dehydration occurs when fluid intake is insufficient to replenish water loss, primarily from sweating and is common among youth athletes. Here are some of the ways that dehydration impacts performance:

  • Reduces blood volume which decreases the body’s sweat rate
  • A lower sweat rate does not allow body heat to escape, increasing body temperature
  • Decreases the rate fluid leaves the stomach, delaying fluid replacement
  • Increases stomach cramping and nausea
  • Increases the body’s use of carbohydrates as a fuel source, making the fuel empty quicker
  • Decreases power output and speed
  • Decreases endurance capacity and increases early onset fatigue.It can also affect sexual health. HealthyMD STD testing can also help you to maintain sexual wellness.
  • Decreases brain function, decision making, attention and focus
  • Decreases ability to perform sports specific skills

What are the Main Causes of Dehydration?

During exercise the body converts energy from food to energy muscles use to produce power, speed and endurance.   This process increases body heat production and the heat produced must be released so that the body temperature does not rise to dangerous levels.  The main way the body dissipates heat during exercise is through sweating.  The evaporation of sweat releases up to 75% of the heat produced during exercise and is an important process that allows body temperature to stay in a normal range.  Sweating is necessary because it helps to rid the body of heat, but in doing so, leads to a loss in body fluids.  Sweat loss can range on average 0.5-2.0 L, up to 3 L or more depending on the duration and intensity of exercise and the weather conditions.  For example, a moderate intensity workout may produce 0.5-1.5 L sweat loss over a 1-hour period. Sweating not only leads to losses of body fluids, but also losses in electrolytes which may significantly impair performance and health if all are not replenished.

What are the Signs and Symptoms of Dehydration?

  • Decreased urine output, urine color dark yellow or darker
  • Rapid heartbeat
  • Flushed skin
  • Lethargy, excessive fatigue
  • Dizziness, lightheadedness or headache
  • Thirst (not always)
  • Gastrointestinal cramping, nausea, diarrhea, or vomiting
  • Heat sensations or chills
  • General discomfort
  • Disinterest in the game, inability to run as fast or play as well as usual

Develop Personalized Hydration Plan

Although sweating is essential in maintaining a safe body temperature during exercise, it is important to replace lost body fluids and electrolytes to optimize your performance and reduce risk of heat related illness.  One way to do this is to develop your own personalized hydration plan.  Follow the steps outlined below to assess your hydration status and develop fluid and electrolyte replacement strategies to optimize hydration.

Hydration Assessment

Three out of 4 youth athletes arrive at practice in a dehydrated state, that means your body fluids before you start to exercise are already low.  This greatly increases your risk for heat related problems such as muscle cramping, heat exhaustion or possibly even heat stroke and definitely interferes with your ability to practice hard and perform well.  Using one of the methods below will give you an estimate of your current hydration status so that you can adjust daily fluid consumption to best meet your needs.  These methods can indicate changes in hydration status but should not be used to diagnose dehydration.

Methods to Assess Hydration Status and Fluid Needs

  1. Urine Color
    • Upon waking, examine the color of your first urine void of the day.
    • Compare the color of your urine to a urine color chart, like the one below.
    • Your urine color should fall in the very good to fair categories.
    • If your urine indicates light to severe dehydration, you will need to make a conscious effort to drink more throughout the day.
    • Note, the concentration (color) of urine is affected not only by fluid loss, but also by diet, vitamin and mineral supplementation, food dyes (watch food dyes in some popular commercial sports drinks), and certain medications.
  2. Thirst
    • Thirst in athletes, is generally not a good way to determine if you are drinking enough fluids, especially during exercise.
    • However, there is some evidence that suggests first morning thirst in strongly related to lower body water stores. So, take note if you wake up feeling thirsty as it may mean you are not drinking enough fluids throughout the day.
  3. Change in Body Weight
    • Immediately before exercise, urinate before getting weighed on a reliable scale. It is recommended to weigh in minimal clothing (spandex exercise shorts and sports bra (for girls).
    • Weigh again (on the same scale) immediately upon completion of exercise, wearing the same clothes worn during the pre-exercise weight.
    • The difference in body weight reflects the approximate fluid loss incurred during the exercise bout. The goal is to adjust during exercise fluid intake to minimize fluid losses via sweat.
    • Fluid losses will vary depending upon the duration and intensity of the training, weather conditions (high heat and cold temperatures= greater fluids losses), equipment worn during practice, so you may need to repeat this process for these different scenarios to get a good understanding of your fluid losses over the range of training you do.
  4. Calculate Your Sweat Rate
    • Use the Calculating Your Sweat Rate Table below to determine your own individual sweat rate during exercise training and competition.

Determine Fluid Needs

Identifying how much fluid is lost during exercise is important in planning how much fluid you need to consume to stay hydrated.  Think about drinking fluids as a daily total and to supplement fluid losses before, during and after exercise.


Over half the human body is composed of water so it is vital to drink enough water daily so that body functions are not compromised.  Total water intake includes drinking water, water in other beverages (such as fruit juice, sports drinks, tea) and water that is found in food.  The Dietary Reference Intakes recommends an adequate intake (AI) of water daily acknowledging that there is great variability in the amount of water needed for adequate hydration and health amongst people (See table below).   Another reason why it is so important to monitor your own hydration status and adjust your daily fluid intake.

Before Exercise

Ensuring your daily fluid intake is sufficient is important, as it increases the chances you will start exercise in a normal hydration state.   Thus, the goal before exercise is to start training or competition well hydrated.  In sport activities that involve heavy sweating, drink 8-24 ounces of fluid 4 hours before the event, this allows enough time for the fluid to be absorbed and the excess lost as urine.  However, if urine output is still low and/or dark in color, drink another 8 ounces of fluid 2 hours before the event.  Remember more is not better!  There is no benefit to drink excessive amounts of fluid before exercise as it will only increase body weight and the potential need to urinate during exercise.

During Exercise

Better hydration means better performance.  Athletes should be encouraged to drink during training and competition and if and when they are thirsty.  It is especially important if the exercise duration and intensity are high, hydration status is compromised at the onset of exercise and ambient temperature is hot and humid.  General guidelines suggest younger athletes (9-12 y) should aim to drink 3-5 ounces of fluid and athletes (>13 y) drink 5-8 ounces every 15-20 mins during games and practice and be encouraged to drink whenever thirsty.  A gulp of fluid is approximately 1 ounce.  Calculating your own sweat rate (See Calculating Your Sweat Rate Box above), allows you to customize fluid intake during exercise.

After Exercise

Lastly, remember to replace fluid losses following exercise by drinking 16-24 oz fluid per pound lost during training or competition.  If you are unable to weigh yourself, aim to replace fluid losses by drinking 2 ml fluid per pound of body weight.  For example, a 145-pound athlete should drink approximately ~290 mls (145 pounds x 2 ml=290

Choosing the Right Beverage to Drink During Exercise

The best beverage to drink during exercise depends on the duration of the event or workout and the climate.  Use the table below to guide you in selecting the best type of beverage to consume.

A final consideration, research has shown that youth athletes given only water do not drink enough to replace fluid and electrolyte losses as completely as they do when they drink sports drinks or other flavored beverages.  Offering beverages, like sports drinks, that taste good, encourage athletes to drink and have the right blend of carbs, sodium, chloride and potassium help to achieve an optimal hydration status, keeping athletes safe and performing their best!