Fluid loss And dehydration- Do we really need that much water?

For so many of us particular marathon and ultra runners, the message that drinking too little could lead to serious dehydration and poor performance  is a big part of race day preparation. For years, the ACSM (American College of Sports Medicine) has been telling us to drink as much as 125ml-250ml of water every 15 minutes of running. The fear? That if our water levels drop too low (more than 2% of your body weight below normal) then we will develop symptoms of dehydration- confusion, headaches, weakness, dizziness and eventually the risk of hyperthermia

This constant message both from coaches and drinks companies has now resulted in quite the opposite; people are over hydrating in an effort to avoid a poor performance. Head to any road race longer than 5k and you will see water stations dotted along the course, crowded with keen athletes trying to get as much fluid into their system

So do we actually NEED to consume so much water?

Well, let’s take a look at the work of Dr. Trim Noakes, author of the Lore Of Running and a hugely acclaimed scientist in running physiology. Noakes suggests that there is actually isn’t evidence of ill effects of poor performances from athletes who drink little of nothing. In fact the author goes on to say that the athletes who suffer the most dehydration are typically the elite guys at the front of the races, the ones with the better performances, who are working at a considerably higher intensity than the rest of the field. So why is this the case?

Noakes suggests that the symptoms of dehydration that we would normally expect are not actually from the lack of water at all, but instead from a reduction of blood sodium levels (called hyponatraemia) and that this reduction can happen no matter how much water we drink. It is this reduction in blood salts that causes the small number of race day facilities you may have witnessed in the big city marathons. Eventually hyponatraemia can result in brain swelling, fluid build-ups in the lungs, and cardiorespiratory arrest if it reaches dangerous levels

So if it’s nothing to do with dehydration, then why do runners still suffer some of these symptoms with the elite athlete doesn’t? This is mainly because better trained athletes are much better able to regulate their own body temperature ( a mechanism  that doesn’t actually require much water to regulate), and they lose less sodium due to lower sweating rate than moderately trained runners. The overriding message from Noakes is that you should only drink when thirsty, and even then in moderation. Instead consider the use of isotonic fluids or salts replacement products, couple with a moderate amount of water on race day, and avoid the excessive water consumption that we typically use

Putting this into practice

1. Experiment with different volumes of fluids and see how you respond. Everyone is different, so find what works for you through your own experimentation and not just based on some recommendations, you have been given or read
2. Be aware of the early signs of hyponatraemia; the only fatigue from exercise should be from the muscles working too hard or laboured breathing and not any signs of weakness, dizziness or lack of concentration. If you have ever reached this stage, it’s time to seriously reconsider your preparation for races and training.
3. Avoid taking any fluids that don’t contain salts during longer races. This is also a good opportunity to supplement your body with carbohydrates using sports drinks that contain both sugar and salts. Try not to drink water alone
4. As with everything in sport science, there are expectations to the rule. If you find your previous practices have been working fine, think twice before making any big changes, There is still an opportunity to experiment in training however, so consider trying both options in moderation and see how the you respond in each case.

By Joe Warne