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​​Fluid replacement   - how much do we really need to drink during exercise?


The popular misconception of players having to drink copious amounts of water to counteract the risk of dehydration can be dangerous in itself...


Contrary to the popular image portrayed in the media, fluid replacement isn’t just about throwing water bottles on to the field.  It’s more about managing fluid intake overall. 

Instead of just concentrating on match days, the emphasis needs to be on getting the fluid intake right during the week as well.  Players also sweat in training too, don’t they? 

So by ensuring that fluid replacement is addressed continuously, by the time match day comes around, the body will be properly hydrated.

However, it’s not all about drinking water for drinking’s sake.  Although taking in adequate amounts of water is vital if dehydration is to be avoided; the thinking on how much water to actually drink has changed in recent times. 

For years we were told that by the time you feel thirsty, then you are already dehydrated.  Now this is being questioned.

The potentially fatal condition referred to as Exercise-Associated Hyponatremia (EAH) is known to occur as a result of consuming fluid far in excess of what is needed during exercise or sport (Hew-Butler et al, 2015).

But since the first scientific description of EAH by Noakes et al in 1985, interest in the subject has gathered momentum and previous concepts have been queried.

Management plans have been developed as our knowledge of the condition has evolved. These include recognition of the condition by medical professionals and prevention through increased awareness of fluid consumption levels by athletes and coaches.

As a topic, the correct amount of fluid required to be ingested during sport or exercise has been debated at length.  Central to the discussion has been the statement by Noakes et al (2005) that EAH can be prevented by ensuring that athletes do not drink to excess during exercise. 

On behalf of the Hyponatraemia Guideline Development Group, Spasovski et al (2014) defined hyponatremia primarily as a disorder of the body’s water balance, with a relative excess of total body water compared to total body sodium and potassium content.

This results in the body having a reduced concentration of sodium and potassium in the blood; and as the excess fluid moves into the tissues this can lead to swelling.   

Symptoms of hyponatremia can vary from relatively mild to severe and life-threatening.  In severe cases, swelling of the brain can occur together with increased inter-cranial pressure.  Deaths attributed to EAH have been recorded in marathon running and in American Football (Hew-Butler, 2018).

Players being made to “drink to order” can be a risky practice based on current evidence stating that the biggest risk of sustaining Exercise-Associated Hyponatremia is excessive fluid consumption over and above that dictated by the body’s own thirst mechanisms (Hew-Butler et al, 2017).

The Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, (2015) gives clear recommendations with regards to fluid intake. 

The main recommendation from that conference, and subsequent scientific updates, is to be to be guided by your own individual thirst levels as to how much fluid is needed.

So the key, then, is to apply common sense instead of drinking for the sake of it. 

Education, as always, plays a huge part in this but getting the message across to players and coaches can sometimes be the most difficult part. 

We now know that the popular misconception of players having to drink copious amounts of water to counteract the risk of dehydration can be dangerous in itself.

Based on current and recent research, therefore, although it’s important to drink and rehydrate during exercise; it’s equally important not to drink too much.

References:


Dreyfus JH, (2015).  Every year more athletes are injured by hyponatremia than dehydration.  Available from:  http://www.mdalert.com/article/every-year-more-athletes-are-injured-by-hyponatremia-than-dehydration   Accessed 12th August, 2018.

Hew-Butler T (2018).  Young athletes should stay hydrated, but too much water can be deadly.  The Conversation.  Available at:  https://theconversation.com/overhydrating-presents-health-hazards-for-young-football-players-100365  Accessed 12th August, 2018.

Hew-Butler T, Dugas, JP,  Fowkes-Godek S, Hoffman MD, Lewis DP, Maughan RJ, Miller KC, Montain SJ, Rehrer NJ, Roberts WO, Rogers IR, Rosner MH, Siegel AJ, Stuempfle KJ, Verbalis JG, Winger JM, (2015).  Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015.   Clinical Journal of Sports Medicine.  Vol. 25 (4); 303 – 320.

Hew-Butler T, Loi V, Pani A, Rosner MH (2017).  Exercise-Associated Hyponatremia   - 2017 Update.  Frontiers in Medicine (Lausanne). Vol.4; 21.

Noakes TD, Goodwin N, Rayner BL, Branken T, Taylor RK (1985).  Water intoxication: a possible complication during endurance exercise.  Medicine and Science in Sports and Exercise.  Vol. 17 (3); 370 - 375

Noakes TD, Sharwood K, Speedy D, Hew T, Reid S, Dugas J, Almond C, Wharam P, Weschler L (2005). Three independent biological mechanisms cause exercise-associated hyponatremia: Evidence from 2,135 weighed competitive athletic performances. Proceedings of the National Academy of Sciences of the United States of America.  Vol. 102 (51); 18550 – 18555.

Spasovski G, Vanholder R, Allolio B, Annane D, Ball S, Bichet D, Decaux G, Fenske W, Hoorn EJ, Ichai C, Joannidis M, Soupart A, Zietse R, Haller M, Van der Veer S, Van Biesen W, Nagler E (2014).  Clinical practice guideline on diagnosis and treatment of hyponatraemia.  European Journal of Endocrinology. Vol. 170; G1 - G47.


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