Soweto Marathon

Fluid intake during a marathon

2015-10-20 08:45
running,marathon,runners,race,fluid,fluid intake,

Sometimes a figure is given along with this advice: at least 1 litre of fluid per hour should be ingested during a long distance race. However, ingesting such a large volume is unnecessary and may even be dangerous.

The common belief is that it is essential to avoid becoming dehydrated during a marathon, as this is a very dangerous condition. However, dehydration is seldom a problem. Nevertheless, runners force themselves to drink as much as possible. In the majority of runners this will result in an excess fluid intake and they will stop and urinate during the race.


In a small percentage of runners, however, the fluid will accumulate and a condition called hyponatraemia will develop. This is when the concentration of sodium in the body becomes very low due to the extra fluid and is therefore also known as water intoxication.

Slower runners, and runners who stop and walk frequently during the race, are the most likely to develop hyponatraemia because their sweat rates are fairly low and they have ample time to ingest sufficiently large volumes of fluid to potentially cause the development of the condition. Ironically, hyponatraemia is more dangerous than dehydration.

Handy Tips

There are various ways to combine both fluid ingestion and carbohydrate ingestion.

  • One is to ingest approximately 600 ml per hour of undiluted “Coke”, which is a 10% carbohydrate drink or “Powerade” during the race, therefore supplying about 60g of carbohydrate per hour. These drinks will be supplied at the seconding tables.
  • A second regimen to use if you do not tolerate undiluted Coke or Powerade very well, is to ingest a mixture of Coke and water. Since this will not supply sufficient carbohydrate, supplementation with additional carbohydrate in the form of corn syrup, or equivalent, will be necessary.
  • Thirdly, if only water is ingested, then a large amount of additional carbohydrate must be supplied from other sources to give a total carbohydrate ingestion of around 70g per hour. Typically, one sachet of corn syrup will provide approximately 20 g of carbohydrate.

Whichever fluid replacement regimen is followed, it is important to test it before the race.

By Exercise Physiologist, Dr Andrew Bosch - Head of Running Division of the Discovery Health High Performance Centre of the Sports Science Institute of South Africa.


Read News24’s Comments Policy publishes all comments posted on articles provided that they adhere to our Comments Policy. Should you wish to report a comment for editorial review, please do so by clicking the 'Report Comment' button to the right of each comment.

Comment on this story
Comments have been closed for this article.


Besides the 'Big 3' of rugby, cricket and soccer, which of the 'smaller' sports in South Africa do you enjoy the most?

Love 2 Meet
English Premiership flutter

Take Sport24's "expert" tips at your peril...

Sport24 on Twitter

Follow Sport24 news on Twitter


The 2018/19 Absa Premiership season is in full swing. Will Mamelodi Sundowns retain their title? Or can one of Kaizer Chiefs, Orlando Pirates, Wits, SuperSport United - or another team perhaps - snatch glory from the Brazilians? Be sure to visit Sport24 for all the latest news!

Latest blogs

Twitter Follow Sport24 on Twitter

Facebook "Like" Sport24's Facebook page

WIN Enter and win with Sport24!

BlackBerry Stay in the loop on your BlackBerry

RSS Feeds Sport news delivered really simply.

There are new stories on the homepage. Click here to see them.