How to Stay Hydrated | Your Guide to Rehydration in Exercise

On average the human body consists of 60% water but can vary between 45 and 75% depending on age, height, weight, gender and body composition (Dunford and Doyle 2008).

As its summer the temperature is increasing, this alongside an exercise regime, puts an increasing importance on staying hydrated.

What Is Hydration?

The level of hydration somebody can experience usually consists of 3 different levels:


When the body has an excess amount of water.


This should be the target level, this is when the amount of water in the body is appropriate to meet all of the bodies needs.

Hypohydration or Dehydration

When there is an insufficient amount of water within the body.

Both Hyper and Hypo hydration are two levels that can be dangerous in the human body.

The body has a very effective system of keeping the Osmoralities (Concentrations) as they should be, when sodium is lost through sweating the body is able to maintain homeostasis (Sawka, Wenger & Pandolf 1996 In Campbell & Spano 2011)

Fluid Balance during exercise

benefits of hydration

As mentioned there are two extremes in relation to hydration. The least common is Hyperhydration. The main negative effect of this is Hyponatremia.


This is when the body has a low concentration of Sodium. This can be caused by excessive sodium loss through sweat and overconsumption of low Sodium beverages such as water. Signs and symptoms of Hypodnatremia include (Montain 2008 IN Seebohar 2011):

Symptoms of Hyponatremia Untreated Hyponatremia
Muscle Weakness
Brain Swelling
Pulmonary Edema
Cardio respiratory Arrest

The more common extreme that people witness is dehydration. As you know an increase in core temperature when exercising causes the body to produce sweat to help cool down. Everybody reacts differently to exercise giving a varied amount of water and electrolyte losses. An extensive loss of water and electrolytes will result in dehydration.

Many things can affect how quickly an individual becomes dehydrated. These include: Age, body composition, clothing or equipment worn, the environment and the individuals metabolic rate (Mcardle, Katch, & Katch 2006; Godek, Bartolozzi, Burkholder, Sugarman & Peduzzi 2008).

Symptoms of Dehydration | (NHS 2015)

Moderate Dehydration Severe Dehydration
Dizziness or light-headedness
Dry mouth, lips and eyes
Passing small amounts of urine infrequently (less than three or four times a day)
Feeling unusually tired (lethargic) or confused, and you think you may be dehydrated.
Dizziness when you stand up that doesn’t go away after a few seconds.
Not passing urine for eight hours
Weak pulse
Rapid pulse
Low level of consciousness

Effects of Dehydration

Being dehydrated and experiencing the above mentioned conditions can be huge problem and has many detrimental effects, it increases risk of life threatening conditions such as heat injuries and heatstroke (Noakes 2003), it also has a large effect on performance.


With it being the summer, people are often more active, you should be more careful in the heat and focus on your levels of hydration, the heat prompts greater performance losses compared to performance in cooler conditions due to the added stress that this has on the body during heat exposure (Murray 2007).

A loss of just 2% bodyweight when exercising can reduce performance in both normal and hot temperatures (Maughan and Sherrif 2008).

Dehydration has also been shown to:

Reduce strength by 2%

✓ Reduce power by 3%

✓ Reduce high intensity endurance exercise by 10% (Judelson, Maresh, Anderson, Armstrong, Casa, Kraemer & Volek 2007).

This effect that dehydration can have on performance is key, for not only athletes but for anybody who is trying to improve their performance. Endurance performance has been shown to drop due to bodyweight losses of 2-7%, specifically in environments above 30°c (Cheuvront, Carter III & Sawka 2003), demonstrating that dehydration can have a premature effect on fatigue, due to thermoregulatory changes, cardiovascular strain and rapid glycogen depletion resulting in negative muscular metabolism (Murray 2007).


#1 Importance of hydration

A study by Peyreigne, Bouix, Fedou, & Mercier (2001), found that exercise induced Growth hormone response was reduced when exercise was performed without the intake of water. This shows the importance of hydration as a valid part of a nutrition plan, specifically when trying to add muscle mass. When developing muscle and strength, hydration has shown to be essential in enabling the most positive benefits of training.

However, dehydration has been shown to have detrimental effects on training adaptations, by increasing the concentrations of catabolic hormones cortisol and norepinephrine, reducing the effects of anabolic hormone release such as testosterone, but also interestingly altered metabolic function, by increasing the release of insulin due to the increase in glucose, this reducing the effects of fat metabolism (Judelson, Maresh, Yamamoto, Farrell, Armstrong, Kraemer & Anderson 2008).

#2 Hydration in Soccer

Edwards, Mann, Marfell-Jones, Rankin, Noakes & Shillington (2007) demonstrated that a loss of 2% bodyweight significantly reduces performance in soccer performance. They also demonstrated that performance, with groups who were denied water or allowed simply a mouth rinse, was significantly reduced by 13% and 15% compared to group re-hydrating.

Another study showed that when soccer players lost around 2.2% of their bodyweight during exercise in heats of around 34°c, when both water and electrolytes were supplied using water and sports drinks, a water sodium deficit can still occur, showing that heat has an adverse effect on water loss and promotes the idea of a specific rehydration process required (Kurdak, Shirreffs, Maughan, Ozgünen, Zeren, Korkmaz & Dvorak 2010).

As this research suggests, whether playing competitive sport, developing strength, power or increasing muscle mass, hydration levels and specifically dehydration can have a significant effect on performance.

How To Stay Hydrated

symptoms of dehydration

One of the main problems with maintaining a well hydrated status, is that many people start exercise already dehydrated (Maughan & Shirreffs 2008).

If you have any of the mentioned symptoms, there are a few simple ways to see if you are dehydrated. Assessing how much you urinate, the colour and bodyweight changes are easy methods to quickly assess if you are becoming dehydrated.

✓ Passing small amounts or no urine, dark urine and losing bodyweight are markers to look for.

People who exercise in particular have an increasingly high chance of becoming both dehydrated and hyponatremic. It is essential to get the correct blend of electrolytes and water in order to rehydrate and keep hydrated.

When rehydrating, you should not consume so much that you gain weight past your starting weight, electrolytes, in particularly sodium if sweat loss is high. It is essential that rehydration consists of both water and electrolyte uptake (Burke 2003).

Recommended Guidelines for Rehydration

(Manore, Barr & Butterfield 2000 & Sawka, Burke, Eichner, Maughan, Montain & Stachenfeld 2007)

Hydration Before Exercise

You should drink enough fluid to fluid to balance fluid losses. 2 hours before it is ideal to drink between 400-600ml (14 – 21oz) of fluid or 5-7ml per kg of bodyweight. Sodium can be consumed to help retain fluid and increase thirst, this should be consumed at a rate of 460-1150mg per litre.

Hydration During Exercise

The aim is to replace fluid lost during exercise. You should aim to consume between 90 to 350ml (3-12oz) every 15-20 minutes of exercise, specifically in exercise lasting more than 90 minutes. Consuming carbohydrates of 6 – 8% concentration can also be advised.

Hydration After Exercise

You need to drink enough to adequately replace sweat losses. This should mean consuming between 450 – 720ml (16-24oz) for every pound (0.5kg) of bodyweight lost during exercise. Water is substantial for rehydration, however it is advised that a beverage or food containing electrolytes such as sodium and chloride are the most beneficial and offer the best rates of rehydration.

Dunford (2006) suggests that if an individual is looking for quick levels of rehydration then, cafeine and alcohol should be avoided during the rehydration period.

So what should you look for?

When choosing a beverage there are some things to consider the concentration it consists of, Isotonic would be the ideal drink:


Less osmolarity than the body thus emptied from the stomach quickly


Higher osmolarity than the body thus emptied from the stomach more slowly


Concentration equal to blood thus resulting in optimal absorption of fluids.


Electrolytes are substances that have the capacity to conduct electricity.  Electrolytes are essential for normal function of cells and organs. The brain, nervous system and muscle function require electrical signals to communicate and work effectively. The four main electrolytes are Sodium, Chloride, Potassium and Calcium.

What do electrolytes do and how can I get them?


Sodium and Chloride

Sodium stimulates water uptake in the small intestine, maintaining fluid levels and the drive to drink. Chloride is often paired with Sodium making sodium chloride, or table salt. The combination of the two help to maintain fluid balance.

Eating regular but small amounts of sodium and chloride specifically after exercise will help to maintain fluid balance.


Potassium builds proteins, breaks down and utilises carbohydrates, build muscle and control acid balance.


Magnesium helps to form bone and teeth and for normal muscle and nerve function alongside the protection against high blood pressure.


The main uses of calcium are for bone and teeth strength development. However it also has many other crucial roles such as call signally, muscle contraction, nerve function and also helps to maintain regular heartbeat.

Foods Rich In Electrolytes

Sodium and Chloride Potassium Magnesium Calcium
– Sports Beverages
– Rehydration Beverages
– Table Salt
– Beef
– Olives
– Cheese
– Sardines
– Spinach
– Turnip
– Kale
– Collard Greens
– Oranges
– Tomatoes
– Oranges
– Melons
– Beans
– Prunes
– Leafy greens
– Nuts
– Beans
– Tomatoes
– Brown Rice
– Wholemeal Bread
– Pumpkin Seeds
– Avacado
– Milk
– Meat
– Fish
– Eggs
– Beans
– Apricots
– Figs
– Asparagus

Take Home Points

Sufficient levels of hydration are key for optimal health

Dehydration can cause headaches, tiredness, fits/seizures and ultimately in extreme cases, death

Dehydration specifically in the heat can reduce sports performance from 2-10%

2 hours before it is ideal to drink between 400-600ml (14 – 21oz) of fluid or 5-7ml per kg of bodyweight

During exercise between 90 to 350ml (3-12oz) should be consumed every 15-20 minutes of exercise, specifically in exercise lasting more than 90 minutes

Post exercise you should mean consuming between 450 – 720ml (16-24oz) for every pound (0.5kg) of bodyweight lost during exercise

Isotonic beverages are the best type to rehydrate as they are optimally absorbed by the body

Rehydration could be achieved through the consumption of both fluid and food products



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