Whether you’re a serious athlete or simply exercise for recreation, it’s important to stay hydrated. Good hydration for optimal performance means getting the right amount of water before, during, and after exercise. As the weather starts to warm up again, it’s time to ditch the winter thermals and start re-focusing on your hydration needs during exercise. With so many drink options available and mixed messages about how much and when to drink during exercise, this article will look at the ‘why, what, when and how’ of hydration.



Water is the largest component in the human body. Water content varies from approximately 45 to 70% of total body mass. For example a man of about 75kg would have a body water content varying between 33 to 53 liters. Water content also varies according to stages of life.

water content in the body

water content in the body

Electrolytes in the body

The water content is divided into intra cellular fluid and extracellular fluid in the body. Water in the body not just plain water, it does contain wide range of electrolytes. Electrolytes are salts dissolved into the body’s fluid. We need electrolytes as much as we need water as they help regulate fluid balance inside the cells and outside the cells in the body, balance the acidity of blood (pH) and aid in muscle function. The main electrolyte that we look at in sports nutrition includes Sodium, Potassium, Calcium, Magnesium, Chloride and Bicarbonate. The water movement in the body is controlled by the concentration of electrolytes on either side of the cell membrane in the body. Sodium is what we need to concentrate on for hydration because water moves wherever the sodium concentration is more. If you eat a balanced varied diet you should be able to cover your electrolyte needs that the body requires.





Benefits of maintaining fluid balance during exercise helps sustain athletic performance through the following:

  • Attenuation of increases heart rate – if your heart rate goes too high, it helps bring it down.
  • Attenuation of increased core temperature – regulates it by sweating to keep it at optimal point
  • Improvement in stroke volume
  • Improvement in cardiac output – how well the heart pumps blood around the body
  • Improvement in skin blood flow – great help to cool your body
  • Attenuation of higher plasma sodium, osmolality and adrenaline
  • Reduction in net muscle glycogen usage – more glycogen to spend on exercise fuel



Here is a list of different terminology to help guide you when you are reading different articles related to hydration.

  • Euhydration – is the state of water balance in the body
  • Hyperhydration – stage of being in positive water balance that is water consumed is more than water excreted by the body. However, it only last for a short length of time
  • Hypohydration – stage of negative water balance that is where water excreted is more than water consumed resulting in dehydration.
  • Dehydration – excessive loss of fluid
  • Rehydration – fluid replacement

The different levels of hydration


Hyponatremia is also known as water intoxication. It is the dilution of solutes in extracellular fluid which can be detrimental to health.

Can occur in:

  • Drinking too much too quick prior to event
  • Poorly conditioned individuals
  • Consuming fluid in excess to losses
  • Use of diuretics
  • Lack of sodium in fluid intake during exercise


  • Muscle weakness
  • Muscle incoordination
  • Disorientation
  • Eventually seizures and coma if not treated




The table below is a general guideline for the average population and how much they should be taking through beverages and foods. Adapted from practical applications in sports nutrition 4th ed. H.H Fink & A.E Mikesky

Tea and coffee do have a mild diuretic effect which can actually dehydrate you. So remember to limit your tea and coffee intake to not more than 2 cups a day. A diet high in fruit and vegetable would mean that you are going to have a lot of water from these food sources that can amount to ½ liter of water. If you do not like to drink water, you can take your water from fruits and vegetables given you eat a fair amount. Here is a list to demonstrate to you how much water is in foods.

Water content in fruits and veg

Water content in fruits and veg



Sweat and exercise

Sweat and exercise

Any physical activity creates heat. We all know when we exercise we get warm; this is all due to the movement of our muscles. It is estimated that you can produce 20 times more heat during exercise than at rest in the body. When the body temperature gets too high, we get too warm, feel dizzy, slow down and get fatigued. So we do need to regulate our body temperature and this is done by heat getting dissipated throughout the body and eventually produces sweat. As the sweat evaporates from the surface of the body the temperature of our body is regulated, cooling us down. Failure to regulate body temperature can be detrimental. Some people find it a bit embarrassing if they sweat a lot during exercise and can put them off exercise, sweating should never be something to be ashamed of. It means we are keeping ourselves at a safe temperature. Bring in a towel. During exercise an average person can lose around 1 liter of water an hour. Most of us think we can replace that after exercise. But would you consume that much fluid at once? Athletes can lose up to 3 liters an hour during intense exercise.  Several factors affect the extent of fluid loss:

  • Temperature and humidity – higher the temperature the higher the sweat loss
  • Clothing – clothes that trap sweat and doesn’t allow the body to cool well forces a greater sweat production
  • Size – people with a large body surface area may have an enhanced sweat production
  • Level of fitness – well conditioned people have a higher sweat capacity. The fitter you are the more you sweat.




Losing water

The best way to estimate how much fluid you lose during exercise is to weigh yourself before and after an hour of exercise. For every 1 kg you lose of weight you lose, it means you have lost approximately 1 liter of fluid from your body. If you are conducting this experiment to find out how much fluid you lose avoid drinking water, check how much you have lost and you will know how much you actually need to drink during an exercise to avoid such drastic loss.








For every athlete, 1ml for every calorie consumed is the guideline. For instance, if your total calorie per day comes to 2500kcal, you will aim to consume at least 2500 ml excluding losses during a work-out. You will need to replace how much water you have lost during a workout based on your weight and replace. If your energy needs increase, you will have to increase your hydration as well for optimal performance.




Dehydration occurs when your body loses more fluid than it takes in. The body does not have enough fluid to carry out normal function. If not replaced, blood volume decreases, places extra strain on heart, lungs and circulatory system. Exercise becomes much harder and performance will drop. Dehydration, as low as 2%, can impair performance. Here is a table that shows the percentage of dehydration and what effects it can have in the body.



Kg lost

(for 68kg person)

Physical Effect
1% 0.7 Increased body temperature
2% 1.36 Impaired performance
5% 3.4 Gastro intestinal problems and heat exhaustion
7% 4.7 Hallucinations
10% 6.8 Circulatory collapse


The symptoms of dehydration includes the following:


A simple way to make sure you’re staying properly hydrated is to check your urine. If your urine is usually colorless or light yellow, you are most likely well hydrated. Dark yellow or amber-colored urine can be a sign of dehydration. Below is a hydration chart, this indicates dehydration through urine. However, it’s good to remember that multivitamins, b-complex or consumption of beets or asparagus can affect the colour of your urine. So, it is a just a general guideline at what we should aim for.




You want to ensure you are fully hydrated prior to exercise, prevention is better than cure. Aim to drink 5-7ml per kg of body weight at least 4 hours before session. Be careful not to overhydrate as that can result in hyponatremia. For instance: a 55kg athlete would need 275 to 385 ml and an 80 kg athlete would need 400 to 560 ml. If you working out in the morning, you can bring the water in bed and make sure you do drink enough water during the exercise to prevent dehydration in this case.


We want to drink fluids during exercise to replace losses from sweating and to provide us with source of energy during exercise. Addition of small amount of salt helps replace losses during exercise sustains ‘drive to drink’. That would be mainly for people who have been exercising for more than 60 minutes or more.  Always aim to replace 80% of losses whilst exercising.


Anyone that is exercising for 1 hour or more of intense exercise will likely experience some degree of dehydration. For those who work out and train every day, post exercise fluid consumption become an important part of the food regime. Post exercise rehydration is vital for regular exercises. Always have a drink close to hand when you complete your work out. Drink containing carbohydrates and sodium more effectively than plain water.  More will be addressed in our article about hydration drinks.


Hopefully you now have a better understanding of hydration needs and realise that there is no ‘one size fits all’ approach when it comes to drinking during exercise. Here’s a quick summary of tips for optimising your hydration plan:

  • Consume as much fluid than can be tolerated immediately (500ml) after exercise
  • 250ml every 15 minutes for 3 hours after
  • Post exercise fluids should contain both sodium and carbs
  • Know how much you lose during your session.
  • Aim for pale yellow urine over the day

Watch out our space for hydration drinks and sports drinks next.




  1. The importance of good hydration for work and exercise performance. Nutr Rev. https://www.ncbi.nlm.nih.gov/pubmed/16028568.


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