Staying Hydrated or Over-Hydrating

Most people are aware of the importance of staying hydrated, with some research stating that a 2% drop in hydration will result in an 11% drop in physical performance. However a lot of these studies are funded by drinks companies and sometimes can be somewhat biased or one sided. Contrasting research has shown that hydration levels don’t have quite the dramatic effect on performance as stated in previous studies and that the main issue is over-hydrating.     

The majority of our body is made up from water and our body needs water to function properly. It creates an aqueous environment for many of our bodily functions to take place but is also a key contributor in expelling waste or by-products produced by the body. As discussed before, becoming dehydrated can have a dramatic effect on physical performance; however to what degree is questionable. Research has shown that dehydration can affect the mobility of joints through reduced flexibility and joint stiffness. Starret talks about hydration, by comparing it to a well-oiled car engine, as the body needs water so that the body’s tissues can slide over each other and move more freely. Studies have also shown that dehydration can effect cognitive performance as the brain needs a constant supply of blood to function properly. So it makes sense to stay hydrated; however can you be too hydrated?

A number of studies by Noakes suggested that actually dehydration isn’t the major threat but that over-hydrating (hyponatremia) is a much bigger and more serious issue.  When Noakes looked at the hydration levels of ultra-marathon runners, he found that the top runners were coming in dehydrated but also found that there a number of severe cases of hyponatremia. Our bodies can only absorb between 800-1000ml of water an hour, and any more taken in will simply start collecting in the body. This will dilute the electrolytes (salts and minerals), which can affect our muscular contractions but also reduce the further absorption of water through the kidneys.  The mistake a lot of people make on a hot day, is to wait until they are super thirsty then start quickly knocking back large volumes of water thereby potentially becoming over hydrated.

Some of the symptoms for dehydration are headaches, dizziness, tiredness, muscle fatigue and cramps. However these are the same symptoms of hyponatremia. Therefore, some people could mistake these symptoms of hyponatremia for dehydration and start drinking even more water making the situation even worse. This is especially because of the public’s perception of hydration on performance, which is based by the marketing of a number of drinks companies.

An indicator that the British Army use to identify dehydration is the colour of your urine, stating that clear colour urine is a good indicator for being hydrated. However clear urine could also indicate that your electrolytes have become too diluted for the kidneys to absorb the amount of water drunk. Constantly urinating with clear urine could be an indicator of over-hydrating. This is why it is recommended that you add a pinch of salt or electrolytes to water you consume without a meal. A good way to test hydration levels through urine is to use a pH urine stick and look at the SG marker. This indicates the solution density of the urine identifying your level of electrolytes. Normal hydration status is 1.005 to 1.015, slightly dehydrated around 1.020 and dehydrated over 1.025.

Thirst and a dry mouth can be a good early indicators for being dehydrated, but thirst can be a bit subjective. As the body becomes more dehydrated it will start to draw water from the skin and bones making the skin less elastic and the bones softer. A good test for identifying dehydration is to pinch the skin, if you are hydrated the skin will spring back into place quickly however if dehydrated the skin will slowly move back into place. Another test is to push down on the tibia bone (bone at the front of the shin) if you leave a dent then this can be an indicator for dehydration.


During long endurance events or in hot conditions it is best to drink little and often, as opposed to drinking in large volumes at once. This is to avoid our kidneys being other worked and enable to absorb the water.

Add electrolytes or a pinch of salt to water you consume without a meal. This is so that there is a balance of electrolytes to water so that it can be absorbed by the kidneys.

Experiment with the volume of water consumed and the degree of electrolytes consumed in your training and how you feel. You can also link this to your performance in your training.

If you are urinating clear urine frequently, there is a good chance that you’re over-hydrated and your kidneys are not absorbing the water. If you think that this is likely, it might be advisable to add some electrolytes or salts to your drink.  

When you're exercising, you should only drink what you lose in sweat. One way to assess this is to conduct a sweat test to give you an idea of your sweat rate per hour. This can give you a rough idea of your sweat rate if you can recreate the environment and intensity of your task, although a major issue is that there are a number of different factors that can affect the rate at which you sweat and it varies between individuals.

Sweat Test Procedure

Weigh yourself in your underwear, and then train for 1hr in the session specific to your task. Weigh yourself in your underwear after the session and work out your difference in weight.

1g of weight = 1ml of water lost

The most important thing when it comes to staying hydrated is to create the right balance between water and electrolytes. However this can be easier said than done



Barr, Susan I. "Effects of dehydration on exercise performance." Canadian Journal of Applied Physiology 24.2 (1999): 164-172.

Grandjean, Ann C., and Nicole R. Grandjean. "Dehydration and cognitive performance." Journal of the American College of Nutrition 26.sup5 (2007): 549S-554S.

Joyce LeFever Kee. “Fluids and Electrolytes with Clinical Application." 2010 

Murray, Bob. "Hydration and physical performance." Journal of the American College of Nutrition 26.sup5 (2007): 542S-548S.

Noakes, Timothy David. "Dehydration During Exercise: What Are the Real Dangers?" Clinical Journal of Sport Medicine 5.2 (1995): 123-128.

Noakes, Timothy D. "Hyponatremia in distance athletes: pulling the IV on the ‘dehydration myth’." The Physician and Sports Medicine 28.9 (2000): 71-76.

Noakes, Timothy D. "The hyponatremia of exercise." International journal of sport nutrition 2.3 (1992): 205-228.

Starret, Kelly. “Ready to Run.” Victory Belt Publishing. 2014