Fluid Replacement for Active Individuals to Avoid Dehydration

Healthy woman drinking water
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Fluid replacement for active individuals and athletes is under constant review for improvement. In order to perform at your best, maintaining adequate hydration is essential. Unfortunately, many athletes and those physically active are competing and exercising without proper fluid balance.

The 2017 National Athletic Trainer’s Association (NATA) position statement on fluid replacement indicated more than 50% of athletes participating in professional sports, collegiate athletics, high school, and youth sports come to workouts lacking sufficient water intake. Fortunately, this can be managed with the right fluid replacement strategies in place.

Understanding Water Fluid Balance

Water intake is essential for the human body to function at optimal levels. Water is also a major component of the body with about 79% found in your muscle tissue. It’s also distributed within and around your cells, and the fluid part of your blood. Water has an important job of keeping your body in balance (homeostasis) and is considered the most important nutrient in sports nutrition.

Fluid balance is maintained within a very small margin (+1% to -1%). When your body water is at 1%, you would be in a state of hyperhydration or excessive water intake. When your body fluid levels are at -2%, you’re lacking adequate fluid replacement (hypohydration). Many active individuals exercise while hypohydrated, which may cause decreased athletic performance and increased health risks. 

Proper fluid replacement promotes the ability for you to remain within a normal body fluid range. The right fluid balance helps to:

It's important to keep in mind that what works best for you will be different for someone else since body fluid losses and needs are individual. This is also the reason why general fluid replacement guidelines may not be applicable to you as an athlete or an active adult. The American College of Sports Medicine (ACSM) states that active individuals should not rely on thirst alone for their fluid replacement needs and that other factors for rehydration should be taken into account.

What Are the Different Types of Hydration?

There are several conditions and varying states of hydration potentially affecting your body. Use the following terms and definitions for fluid replacement, balance, and hydration to stay informed:


Having an optimal total body water content is regulated by the brain. The body systems function most efficiently in a state of euhydration.


Hyperhydration means there is excessive total body water content or that you've consumed too much water. The body normally excretes excess fluids but is unable to perform this function in this state.

Exercise-Aassociated Hyponatremia (EAH)

Hyponatremia is a fluid-electrolyte condition caused by a decrease in sodium levels, typically associated with persistent water intake, during prolonged physical activity. Exercise-Associated Hyponatremia (EAH) is potentially life-threatening.


This refers to the process of losing body water. Body water losses typically occur from sweating, urine, respiration, feces, or vomiting. 


Hypohydration is a body water deficit caused by acute or chronic dehydration. This condition is determined by an assessment of athletic level (mild to moderate hypohydration = 2% to 5% and severe hypohydration = >5% body mass deficit).

Athletes with a body water deficit greater than 5% may experience impaired performance, extreme thirst, headache, and other symptoms. Severe fluid deficits are difficult to replace, even with extended recovery time.

Drinking ad Libitum

Drinking ad libitum (ad lib) means “drinking at one's pleasure” or consuming fluids when desired and of the preferred concentration, flavor, consistency, temperature, etc.

Drinking to Thirst

Similar to ad libitum, drinking to thirst means that you consume fluids as your thirst dictates. This strategy involves consuming fluids when thirsty and drinking enough to limit the sensation of thirst before and throughout the activity. However, this may not be an effective strategy alone for some very active individuals.

Fluid Replacement: Benefits and Guidelines

The benefits of proper fluid replacement include maintaining athletic performance, regulating heat transfer, sustaining mental focus and mood, and supporting exercise recovery. Without adequate fluid intake, or even consuming too much water, you can compromise these benefits.

Athletic trainers, coaches, and exercisers should be able to recognize the basic signs and symptoms of dehydration (thirst, irritability, and general discomfort, followed by headache, weakness, dizziness, cramps, chills, vomiting, nausea, head or neck heat sensations, and decreased performance).

Follow these fluid replacement guidelines for athletic trainers, healthcare providers, and active individuals:

Basic Hydration Protocols

Established hydration protocols along with rehydration strategies should be specific to each individual. Hydration protocols should be designed according to the sweat rate, sport, and environmental conditions. Athletes and exercisers should begin all workouts well hydrated, and fluid replacement beverages should be accessible during training sessions.  

Pre-Exercise Hydration

Very active individuals should consume approximately 17 to 20 fl. oz. of water or sports drink 2 to 3 hours before exercise, and seven to 10 fl. oz. of water or sports drink 10 to 20 minutes before exercise.  

Post-Exercise Hydration

Post-exercise hydration to correct fluid losses during physical training or an event should contain water to restore hydration status, carbohydrates to replenish glycogen stores, and electrolytes to speed rehydration.

Fluid replacement should be based on individual sweat and urine losses maintaining hydration at less than 2% bodyweight reduction. This generally requires 7 to 10 fluid ounces every 10 to 20 minutes.

Fluid Replacement Beverages

Rehydration is recommended to be completed within 2 hours post-exercise. Fluid replacement beverages should be consumed at a cooler temperature (50-59 degrees F). Sodium chloride (salt) in fluid replacement beverages should be considered when physical training exceeds 4 hours, or when inadequate access to meals or no meals are consumed, or in hot environmental conditions.

Carbohydrate Intake

Active individuals should maintain proper carbohydrate intake as part of hydration and rehydration protocols before, during, and after exercise sessions or sporting events. 

Hydration Status

You can monitor your hydration status by calculating your sweat rate by weighing yourself prior to an intense one-hour exercise session and again upon completion of the session without hydrating or urinating within the one-hour period. 

Sweat Rate Calculator

Sweat rate = pre-exercise body weight - post-exercise body weight + fluid intake - urine volume/exercise time in hours.

Hot Weather Exercise

Heat can alter sweat rate and individual fluid-replacement needs. Increased sodium intake may be warranted. Coaches might monitor the hydration levels of an athlete exercising in a warm environment. Weight class-specific sports (e.g. judo, wrestling, bodybuilding, rowing) should mandate a hydration status check at weigh-in to ensure the athlete is not dehydrated. 


The practice of hyperhydration is not supported by health and fitness experts. Hyperhydration involves ingesting a pre-exercise glycerol and water beverage. Glycerol consumption side effects may include gastrointestinal distress and headache. 

Child Athletes

Parents and coaches of child athletes should understand both rehydration and the signs of dehydration. Similar to adults, children should minimize time spent exercising in the heat and maximize time for a fluid replacement. If your child exhibits signs or symptoms of dehydration they should be removed from the activity promptly.

When you understand the importance of fluid replacement as an essential part of physical fitness, you gain the ability to maintain both optimal health and athletic performance.

How to Maintain Euhydration

All physiological body functions are influenced by your hydration status. The body will attempt to balance altered fluids lost through increased internal temperature and sweat, for example. Fluid losses coming from sweat are the primary reason for dehydration in the exerciser.

Euhydration is having balanced total body water regulated by the brain and maintaining your body functions at optimal levels. This means you’re doing a great job monitoring your water and electrolyte intake before, during, and after exercise sessions.

If adequate fluid replacement is not consumed to offset the rate of water lost through sweat, progressive dehydration can occur. The goal as an active individual is to avoid dehydration and maintain a state of euhydration. Here are some essential euhydration tips to follow:

Calculate Your Sweat Rate

Knowing your sweat rate ( helps properly maintain hydration status and replenish fluid loss during physical activity.

Assess Your Hydration Status

Monitor any changes in your body weight, urine color, subjective feelings, and thirst, which provides cues for needing to rehydrate. 

Consume a Balanced Diet and Get Enough Fluids

Getting enough fuel and ensuring that you're properly hydrated is especially important during the 24 hours before an exercise session or event. Athletes should start physical training sessions or events well-hydrated.

Consuming 500 mL of fluid 2 hours before an event is recommended. When access to meals is limited, a carbohydrate (CHO)-electrolyte beverage can help maintain hydration status, energy, and electrolytes.

Rehydrate During Exercise

Athletes and exercisers should aim to drink fluid quantities equal to sweat and urine losses. A rehydration drink containing sodium, potassium, and CHOs may be helpful to maintain blood glucose, electrolyte balance, and athletic performance for training sessions lasting longer than 50 minutes.

Allow 5 to 10 days to Acclimate to Heat

Athletes and other active individuals who are heat acclimated have fewer fluid deficits associated with dehydration. Avoid excessive water drinking during prolonged workouts (4 hours) to prevent water intoxication (hyponatremia).

Drink a Sodium Rehydration Beverage

Fluid intake shouldn’t exceed sweat loss. Adding 0.3 to 0.7 g/L of salt to hydration beverages is considered safe and reduces the risk of medical events associated with electrolyte imbalances (e.g. muscle cramps, hyponatremia).

Rehydrate with Glucose and Fructose

Rehydration beverages that include glucose and fructose are ideal after exercise since they increase your fluid absorption rate. The amount of glucose in the beverage should be limited to about 2% to 3% (2 to 3 g/100 mL) to reduce the risk of gastrointestinal distress and maintain optimal absorption. 

Athletes and active individuals with medical conditions should consult their healthcare team about their specific hydration requirements to avoid dehydration, which could exacerbate their conditions. 

A Word From Verywell

Maintaining proper fluid balance means much more than simply drinking a glass of water, especially if you’re physically active. The bottom line is that athletes and exercisers should not lose more than 2% of their body mass loss during intense exercise.

Ideally, exercise-related body fluid losses should be replaced within a short time frame. Remember that while you can avoid fluid-balance problems by drinking when thirsty both during and after exercise and by following a healthy, balanced diet, there are other strategies to consider. If you have any questions and concerns regarding your level of physical activity and hydration status, ask your trainer or doctor for guidance.

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Article Sources
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  2. U.S. Department of the Interior. United States Geological Survey. The Water in You: Water and the Human Body.

  3. Thomas DT, Erdman KA, Burke LM. American college of sports medicine joint position statement. Nutrition and athletic performanceMed Sci Sports Exerc. 2016;48(3):543-568. doi:10.1249/MSS.0000000000000852

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