Why you need a hydration plan

Meyken Houppermans, PhD. CrossFit Level 3 Trainer.
Head Coach and Founder
Do you need to drink during Fran*? Probably not, unless you’re choking on your own tears of course. But for athletes who regularly do longer intense workouts, a personal hydration plan is a necessity to optimize performance and health.

At CrossFit Eudokia we teach our athletes to focus on the task ahead and withstand the temptation of taking unnecessary rest, by sipping water for example, because that can compromise the desired high intensity of the workout. You probably do not need water during a short workout. But during longer intense workouts over one hour fluids are necessary. The choice and amount of fluids as well as the timing of the intake strongly affect performance and recovery during and after the workout. Water is not the best option.

Why are fluids so important, what and how much should you drink?

The highlights of this article

·       Adequate fluid intake before, during and after a workout is crucial for performance.

·       A sweat loss of 1 to 2% body weight already affects performance and health.

·       Don't drink water. Isotonic drinks, beer and chocolate milk seem better.

·       Urine and body weight give insight into your hydration state.

·       Men should drink 3 liters and women 2,2 liters per day.

·       A hydration plan is a necessity for athletes who work-out regularly.

·       We explain how to develop your personal hydration plan.

The importance of fluids for performance and health

Humans are homeotherms. This means the body tries to maintain a stable core temperature around 37°C via several physiological and behavioral mechanisms. Physiological mechanisms are for example sweating during exercise to cool down. Behavioral mechanisms are for example drinking hot beverages to warm up when it is cold. A too high body temperature, above 38°C,as well as a too low body temperature, below 35°C, can affect performance and health.  

Sweating is the most dominant mechanism to control body temperature during exercise. Besides containing water, sweat also contains electrolytes. Electrolytes are important for bodily functions such as sending signals from cell to cell for muscle contractions. Not adequately replacing electrolytes during and after exercise, by only drinking water for example, can lead to a water and electrolytes imbalance. This can result in health problems such as dehydration and hyponatremia

A sweat loss of 1 to 2 % bodyweight can already affect performance. For a 70 kg athletes, this means a loss of 0.7 to 1.4 liters during exercise. It can lead cardiovascular problems such as a higher heart rate and reduced cardiac output (the amount of blood pumped by the heart). The risk increases in endurance athletes and athletes working out in a hot environment. [1]  


Dehydration occurs when the loss of fluids is larger than the intake, and the body cannot execute normal functions anymore. Symptoms are thirst, less frequent urination, dark colored pee, fatigue and dizziness.

Dehydration can lead to complications such as heat injury which ranges from heat cramps to a heat stroke; urinary and kidney problems; rhabdomyolysis, low blood volume shock (a drop in blood pressure and oxygen level in the body); and seizure due to imbalance of electrolytes causing involuntary muscle contractions and sometimes a loss of consciousness.[2]

Dehydration of more than 2% bodyweight decreases aerobic, cognitive and mental performance due to increased core temperature, increased cardiovascular strain, increased glycogen utilization (muscle glycogen use is greater in a state of dehydration), altered metabolic function, and altered central nervous system function.[3] 


Rhabdomyolysis, in CrossFit known as ‘rhabdo’, is a syndrome causing release of skeletal muscle contents due to the death of muscle fibers and release of their contents in the blood stream. Although it is a rare condition, it is a risk for certain athletes who take on a very intense long workout, often with movements that require ongoing effort in both the concentric and eccentric phase (such as thrusters).  

Athletes at risk are novel and/ or deconditioned athletes; athletes who push themselves over the edge for a long duration; athletes who progressively scale workouts; athletes who re-entering a sport after a long break thinking they can pick up where left off; athletes with an underlying medical condition; and athletes who start a workout dehydrated and/or in a hot environment.  

Symptoms are dark colored pee (Coca Cola), decreased urination, muscle cramps, swollen body parts, nausea or vomiting, high heart rate and symptoms of dehydration. Rhabdo can lead to kidney failure and even death.[4]  


Hyponatremia occurs when the concentration of the electrolyte sodium in the blood is too low. Sodium helps to regulate water in and around body cells. Hyponatremia can be the result of drinking too much and/or water or a hypotonic or hypertonic sports drink during and after intense exercise. (Hypotonic: the drink contains a lower concentration of salt and sugar than the body. Hypertonic: the drink contains a higher concentration of salt and sugar than the body.) Sodium becomes diluted, water levels rise, and body cells start to swell. This can lead to vomiting, confusion, fatigue, muscle weakness of cramps, seizures and even coma.[5]  

The problem with water and some sports drinks

During exercise and other conditions in which the body gets dehydrated, fluid balance is disturbed and osmolarity of the blood increases. In short: blood gets thicker. To restore fluid balance, the kidneys start to limit urine output and the brain sends signals of thirst, making you drink. The limited urine output and drinking help to restore fluid balance.  

Drinking only water has the opposite effect: Water dilutes the blood and decreases blood osmolarity. In short: blood gets thinner. This creates a fluid imbalance. In response, the kidneys increase urine output and the brain does not send signals of thirst. The increased urine output and reduced intake of fluids (you do not feel thirsty), will lead to an ongoing fluid imbalance and a slower rehydration. Therefor, water is not the best option for adequate rehydration. Hypotonic sports drinks have the same effect. 

Hypertonic drinks are also not the best option. In hyponatremia, the risk from (over)drinking hypertonic drinks might be greater than (over)drinking water or hypotonic drinks, since hypertonic drinks bind water in the body, keeping water levels (too) high.[6] 

Isotonic drinks, beer and chocolate milk

Isotonic sports drinks are a good choice for rehydration. Isotonic means the drink contains the same amount of sugar and salt (sodium) as the body. These drinks do not lead to dilution of blood or changes in blood osmolarity. Urine output will be low and the thirst signal from the brain will be active.


Sugar is necessary for energy provision. If the body lacks energy (sugar), performance and recovery decrease, in the short and in the longer run. It can even attribute to injuries, because muscle function is impaired with a lack of muscle glucose.  

The amount of sugar is relevant: 4 to 8%, or 4 to 8 grams per 100 ml of water. This supports the absorption of water in the gut. If the amount of sugar is too high (hypertonic), absorption is hindered.

For (intense) workouts longer than one hour, carbohydrate intake of 30 to 60 grams per hour is adviced to delay fatigue. The greatest rates of carbohydrate delivery are achieved with a mixture of sugars such as glucose, sucrose, fructose and maltodextrine. (All assuming the athlete is well fed and glucose levels are sufficient before starting a workout). 


Sodium is necessary for several bodily functions such as the function of muscle and nerve cells. Sodium also supports the absorption of water, carbs and protein in the gut and helps to feel thirsty which supports the intake of fluids. Since sodium is the dominant electrolyte in sweat, it should be an important component of a sports drink. 

Ideally the intake of sodium should be the same as the amount of sodium lost in sweat. But that would mean a high intake of salt (around 3 grams of salt per liter water), which increases the risk of health problems. Furthermore, it would not taste great. Most commercial sports drinks contain 20 to 50 mg sodium per 100 ml and 2 to 5 mg potassium, for some (endurance) athletes the absolute minimum.

The ideal daily intake of sodium is 1,5 grams per day with a max of 2,3 grams. The advised amount in a long intense workout of two hours or more is 300 to 600 mg per hour. Assuming recreational athletes exercise on average one to two hours, and have regular proper meals during the day, a commercial sports drink might offer a sufficient amount of sodium and sugar. 

Beer and chocolate milk

Alcohol free beer contains a sufficient amount of sugar to refuel after exercise. Adding some salty snacks helps to restore electrolyte levels. Alcohol is not adviced for numerous reasons, for one the diuretic effect.  

Chocolate milk contains a sufficient amount of sugar and sodium. Yet, the protein and fat in the milk delay rehydration. If quick rehydration is not the primary goal, but recovery from strength training for example is, then chocolate milk can be a good option. [7] 

At CrossFit Eudokia we do not promote alcohol or alcohol- free drinks in relation to sports or a sports environment. The Dutch Health Council advices to not drink alcohol at all, considering the negative health effects. Although alcohol- free drinks might not have the same harmful health effects, for some individuals these drinks can trigger a craving for alcohol. Also, chocolate milk would not be something we advice for the recreational athlete because is it calorie dense and has a low nutritional value.  

Determine your current hydration state

Dehydration before starting a workout can be the result of several factors. Such as a short interval between two workouts and not being fully rehydrated; drinking only water; following a restrictive diet; or taking medication with diuretic effects. Starting a workout dehydrated affects performance and health and should be avoided. Therefor, regularly checking your hydration state is advised. Hydration state can be medically assessed via several biomarkers and requires a medical test. An easier option is to check first morning urine and nude body weight.  

First morning urine

The color of first morning urine is an indicator for hydration state. Pale urine corresponds to normal hydration, and yellow or orange urine reflects dehydration. Color can also be misleading:

Food effects the color of urine. Beets for example give urine a darker color. Also supplements or medication can color urine. Furthermore, drinking tons of water or a hypotonic drink while being dehydrated, can lead to very light-colored urine, long before hydrated state has been reestablished. This implies that indications about hydration state should be based on a long-term and not a one-time check of first morning urine color.  

Nude body weight

Fluctuations of nude body weight is a second indicator for hydration state. Nude body weight is body weight without clothes directly after waking up and urinating. If a person is in energy balance (not on a restrictive diet), and has steady nutritional and bowel habits, a well-hydrated state is assumed if nude body weight is stable with a margin up to 1%,for three or more days in a row. For women this is more than three days, because menstrual cycle effects body weight.  

Do not rely on thirst

Thirst is not always a good indicator for hydration state. Many people do not feel thirsty until they are already dehydrated. Furthermore, the sensation of thirst declines fast after drinking a large amount of fluids despite still being (significantly) dehydrated.[8] 

Advised daily intake

The human body contains approximately 60% water. Under normal circumstances, water balance fluctuates around 0,2% bodyweight per 24 hours, due to loss via skin, respiration, feces, and urine. The average daily urine loss is 1,5 to 2 liters. The advised total daily intake for well hydrated men is 3 liters per day and for women 2,2 liters of fluids per day. This can bewater, soda, dairy products, fruit juices, coffee, and tea.[9]  

If you do not meet the advised daily intake yet, and urine and nude body weight indicate dehydration, the first step is to increase fluid intake as part of your daily nutritional plan.

Develop your personal hydration plan

A hydration plan contains entails the intake of adequate adequate amounts of fluids before, during and after a workout.

Pre-hydrate before the workout

To stay well hydrated, athletes should start pre- hydrating in addition to their regular eating and drinking habits, at least several hours before the workout. The intake of drinks with sodium (and potassium) or eating some salty snacks with the consumption of regular drinks, can stimulate drinking and support retaining of fluids in the body. The advised amount is 6 to 8 ml of fluid per kilogram bodyweight about two hours before the workout.

Prevent dehydration during the workout

The goal of drinking during a longer workout is to prevent dehydration. Regularly drinking an isotonic sports drink in small sips during the workout is advised. Based on the individual sweat rate, an athlete can estimate the required fluid intake during a workout. In a nutshell the content of isotonic sports drink suitable for workouts around one hour:

-       4 to 8 grams of carbohydrates per 100ml

-       20 to 50 mg of sodium per 100ml

-       2 to 5 mg of potassium per 100nl

The adequate fluid intake during a workout depends on the total sweat loss during that workout and hydration state after. It is highly individual and depends on several factors such as body composition, sex and age, type and duration of exercise, hormonal status and environmental conditions.

Calculation required fluid intake during a workout

An easy way to determine adequate fluid intake is to determine total sweat loss during a workout. For workouts of less than three hours in duration this is the difference in bodyweight before and after the workout, corrected for fluid intake and urine loss during the workout. This calculation assumes a well hydrated state before the workout. Ideally the calculation is based on nude body weights, to avoid corrections for sweat absorbed by clothes.

In short: Total sweat loss=  (bodyweight before - bodyweight after the workout) + fluid intake - minus urine lost. One gram of bodyweight = 1 ml of sweat loss.


Calculation of sweat loss:

·       Nude body weight before - nude body weight after = 85 kg- 84.2 kg= 0.8 kg

·       Fluid intake during workout = 0.5 liter

·       Estimated urine loss during toilet visit = 0.3liter

·       Total sweat loss: 0.8 + 0.5 - 0.3 = 1.0 liter(1000ml)

Calculation of sweat rate:

·       The workout takes 50 minutes. The sweat rate is 1,2 liters/hour.

Assuming this rate is representative for the athlete’s sweating behavior under the same environmental conditions, this rate can be helpful to develop a hydration plan for upcoming similar workouts.

Hydration state:

Hydration state  after the workout can be determined by calculating what percentage of bodyweight is lost to sweating during the workout of 50 minutes.  

·       (1 liter sweat loss / 85kg bodyweight) * 100 =1.18% bodyweight lost to sweat


·       This athlete is dehydrated and did not drink enough fluids during the workout. One liter of fluid intake could have prevented this.

Rehydrate after the workout

The goal of rehydration after a longer workout is to replace lost fluids and electrolytes. In general, eating regular meals with a sufficient amount of sodium combined with drinking water after a workout allows for full recovery.

In case of dehydration, such as in the example above, the advice is to drink 1,5 liters of isotonic fluid for every kilogram bodyweight lost. This means 150% of fluid loss should be taken in, considering an increased urine output. Consumption should be in smaller amounts instead of a once. The rehydration advice is an intake of 500 to 700 mg of sodium per liter of water if the workout lasted longer than one hour.  Adding a little salt to meals can also be helpful.[10]


A hydration plan is just as important as a training plan, since hydration can affect performance and health significantly.

Athletes who work-out multiple times per week, at high intensity and/ or for longer duration at a time, should develop a personal hydration plan to prevent dehydration.

Since thirst is not a good indicator for hydration state, and drinking a large amount of fluids declines feelings of thirst despite still being dehydrated, athletes should rely on more objective indicators and determine their own adequate fluid intake.

Athletes should consistently check their hydration state before during and after working out, and develop a hydration plan. Isotonic drinks containing a sufficient amount of carbs and electrolytes, combined with a healthy nutritional foundation can prevent dehydration and enhance performance and health.

Create your own health!©



*CrossFit Benchmark workout Fran: 21-15-19 Thrusters (43kg/29kgbarbell) and pullups. The average time in The CrossFit Open 2016 for men was 4min 48 seconds and for women 5 min 53 seconds.[11]

** CrossFit hero workout Chad: For time 1000 box stepups (20inch box) wearing a ruck pack (20kg/15kg). It takes many athletes over one hourto finish.[12] 


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