Smart hydration for endurance athletes

“How much is enough?” Hydration is an issue that every athlete has faced leading up to an endurance event. Looking at both ends of the spectrum, ongoing debates surround the theories of overhydration and dehydration. Inspired by the research of sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, MD, we reveal ways to find your balance.

hydration, Sbonelo Khwela, Dusi Canoe Marathon

Sbonelo Khwela at the finish line on Day 3 of the 2017 Dusi Canoe Marathon, in KwaZulu-Natal. Photo: Red Bull Content Pool


“We used to be so afraid of dehydration that we told runners to drink before they got thirsty. Now we understand that when you run long distances, a certain amount of dehydration is part of the process. And you don’t need to start sipping fluids until you feel thirsty. The days of chugging water are over.”- Mary Coordt  in Tim Noakes‘ book Waterlogged: The Serious Problem of Overhydration in Endurance Sports.

The first article that we will focus on is Dr Mirkin’s Mild Dehydration Does Not Impair Exercise” which was released in February 2017. He explains that in most cases, over hydration happens to an inexperienced athlete that moves at a very slow pace in an endurance event.

He then outlines the physiology behind overhydration, which is based on the mineral levels in your bloodstream. Ideally, the mineral levels in your blood and your cells should be the same to prevent fluid imbalances. When you are over hydrated (drink too much water without taking in enough minerals) the mineral concentration in your blood lessens and as a result fluid shifts into the intracellular spaces (tissues) and causes tissue swelling. When massive amounts of fluid are taken in, a potentially fatal condition called hyponatremia can occur (which he explains in detail in his article). This can have serious manifestations in the brain especially, and can result in in unconsciousness and seizures.

He brings to our attention, however, that competitive athletes seldom have sufficient time to overhydrate as they are too focused on pushing the pace. He also suggests that fit people can generally tolerate significant levels of fluid loss before their performance suffers.


Numerous controlled laboratory and field studies that have demonstrated that a body water deficit as small as 1.5% can reduce performance in prolonged endurance exercise.  In the journal study titled “Mild Hypohydration Decreases Cycling Performance in the Heat” (Costas et al., 2013), it was revealed  that a 2% loss of body mass due to fluid deficit can lower the heart rate, leading to a diminished ability to pump oxygen to the muscles, and compromised exercise performance.

We will now focus on another article by Dr Mirkin which he published in 2013: “Drink Before Thirst to Avoid Dehydration.” He explains that an athlete should drink before they feel thirsty, because they slow down and lose power long before receiving any signals to tell them that they are dehydrated. He highlights that an athlete won’t even feel thirsty during exercise until they have lost between two and four pints (just under 1-2 litres) of fluid. He suggests that drinking to thirst is no longer an accurate indicator for optimal hydration, and that thirst is a very late sign of dehydration.

So what should you be drinking then?

hydration, Leire Fernandez, Pyrenees, trail running

Leire Fernandez performs in Pyrenees, Spain in August 2016. Photo: Red Bull Content Pool.

From my personal experience as an endurance athlete, I have come to understand that there is no coming back after I have passed the point of dehydration during a race. It is therefore recommended that for those athletes who are competitive and wish to keep performance at a peak during an endurance event, they should rather hydrate as often as possible, taking care to include sufficient minerals in either drinks or food. As mentioned, the risk of overhydration only really applies to those athletes who are not as competitive or who are under trained for an event.

Nutrition sums it up perfectly, whatever the opinion on the matter: “Proper hydration during training or competition will enhance performance, avoid ensuing thermal stress, maintain plasma volume, delay fatigue, and prevent injuries associated with dehydration and sweat loss”

Hydration plan

It is easy to over-complicate your strategy. Dr Mirkin simply suggests that the ideal drink to have during an event is one that tastes good to you, because if it tastes better, you will be more likely to drink more of it. He explains that it also only really necessary to replace sugars and your ordinary table salt during exercise. Water or your favourite drink, plus food containing sugar and salt are effective in maintaining endurance and preventing heat exhaustion.

It is vital to refine your hydration strategy during training. If you are serious about performing at your peak on race day, there are a few things that you can do during training to hone in on your ideal hydration plan:

For those who lean more on the side of drinking to prevent thirst and replace fluid loss, a general and well-known guideline is to weigh yourself before and after exercise, and the difference should not exceed 1-2% (a loss of greater than 2% body mass indicates that you did not sufficiently rehydrate yourself).

Another useful method is to wear a black shirt during training – if you notice salty sweat marks afterwards it could be a sign of excess fluid loss. A sensitive indicator of hydration status is urine colour. You should not be aiming for your pee to be as pale as possible, but on the other end of the scale, you should not be noticing that your urine is coloured dark gold, which is associated with dehydration. A complete absence of urine passage, of course, is indicative of pretty significant dehydration.

For those who agree more with the argument that mild dehydration has minimal effects on an athlete’s performance, sports nutritionist Matt Fitzgerald gives the following, simple advice for endurance athletes:

“Instead of drinking to completely replace the fluid you sweat out during exercise, aim for keeping thirst at bay. Respond to your thirst right away with small amounts of sports drink (instead of water), but don’t allow your thirst to build to the point that you’re forced to guzzle down a full bottle at one time. Taking a few sips about every 10 to 12 minutes will help you stay hydrated and avoid stomach upset.”

He extensively emphasises using sports drinks instead of water: “In short, sports drinks simply hydrate better than water does. Your body absorbs fluids through the gut and into the bloodstream faster when their osmolality, the concentration of dissolved particles in a fluid, more closely matches the osmolality of body fluids such as blood.”

According to the “International Journal of Sport Nutrition and Exercise Metabolism (2014)” a fluid intake in the range of 300 to 500 ml/h may be adequate to remain hydrated during ultra-endurance events under common circumstances. The upper limit of hydration per hour is considered to be around 750-800ml/h.

Back to Dr. Mirkin:

Having looked at both arguments, at the end of Dr.Mirkin’s article about mild dehydration, he encourages the recommendations of the National Athletic Trainers’ Association (Journal of Athletic Training, 2000;35(2):212–224):

• 2-3 hours before competitions lasting longer than an hour: 500 to 600ml of water or sugared drink
• 10-20 minutes before competition: 200 to 300ml of water or a sugared drink
• during the event: 200 to 300ml every 20 minutes.

So go out and find what works best for you, and take deliberate steps to avoid hydration issues that will keep you from performing at your peak.

Read more Dr Mirkin articles at




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