Drowning in hydration advice

The past couple of weeks have seen our first taste of real summer weather, with temperatures climbing to nearly 30°C in the Scottish Highlands! While training in fine summer weather is undoubtedly more enjoyable than slogging through long, cold and dismal winter, it does bring its own challenges – the main one being to keep properly hydrated.Back in the early 2000s, the conventional advice for athletes was to drink ample fluid during exercise – enough to ensure that any losses in body mass incurred through sweating and respiration were minimal, and certainly less than 2% of body mass (i.e. 1.5 litres in a 75kg athlete). This basically meant following a pre-prescribed drinking programme.


Issue number: 305 June 5, 2017



However, this advice has come under increasing attack from a number of sports nutritionists and exercise physiologists who believe that the “hydrate at all costs” approach is at best misguided and at worst, downright dangerous. Indeed, as early as 2006, the renowned exercise physiologist Professor Tim Noakes claimed in a hard-hitting leading article in the British Journal of Sports Medicine that case against “over-drinking” was proven 20 years previously, and that official advice has been influenced by the marketing needs of the sports drink industry.

In the last decade, new findings have emerged that indeed suggest a new approach is needed. For example, a 2011, a review study looked at a large number of previous studies on hydration during time-trial cycling and pooled the data to try and assess the relationship between varying degrees of dehydration and cycling performance(1).

The three key findings that emerged were:

  • When the cyclists drank freely according to their thirst, they tended to perform significantly better than when they didn’t drink enough to meet their thirst needs OR when they drank in excess of their thirst needs (eg when following a prescribed drinking programme).
  • Compared with full hydration, losing up to 4% of bodyweight in fluid loss did not alter cycling performances during out-of-door exercise conditions.
  • Exercise intensity and duration had a much greater impact on cycling performance than did exercise-induced dehydration.

Other recent studies on single groups of athletes provide good evidence that following a prescriptive drinking formula might not be best for performance after all. For example, researchers studied half-marathon performance in runners who followed either a thirst-driven drinking programme, or a prescriptive drinking programme designed to ensure that the runners lost no more than 2% of their bodyweight(2). The results showed that there were no differences in half-marathon times, running pace, average heart rates or core temperatures in the two trials.

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Does dehydration really matter?

The finding that significant dehydration during shorter events (i.e. that drinking is unnecessary) doesn’t really have any negative impact on performance is at odds with the conventional advice, but there are other recent studies that have produced similar results.

In a landmark study, researchers asked 10 cyclists to undergo three separate trials(3). In each trial, the cyclists were dehydrated by 3% of body mass by performing two hours of sub-maximal exercise (walking and cycling) in the heat. Then, the cyclists were infused with a saline solution to replace 100%, 33% or 0% of fluid losses. This left them fully hydrated, 2% dehydrated or 3% dehydrated, respectively.

Why use this procedure you might ask?

The reason is that the cyclists weren’t aware how much fluid was infused, which meant they had no idea of how well/badly hydrated they were (i.e. Any placebo effect was effectively removed!) The cyclists then completed a 25km time trial in the heat (33°C) but with an ambient wind speed of 32kmh to simulate real, outdoors conditions.

During this 25km time trial, their starting hydration status was maintained by infusing saline at a rate equal to their sweat rate. The results showed that although core temperatures in the later stages of the 3% dehydration trial were higher, there was absolutely no difference in performances across all three trials.

We’ll be returning to this topic in the July issue of Peak Performance, where we report on some fascinating new research on the relationship between your rate of fluid consumption and your potential performance gains. In the meantime, if you’re feeling somewhat confused, have no fear – below are some practical guidelines, which incorporates the current best thinking to stay hydrated this summer, with the minimum of fuss!

Yours in fitness,

Andrew Hamilton signature

Andrew Hamilton,
Editor, Peak Performance

P.S. See below for a summary of best practice when it comes to hydration. If you’re serious about achieving your maximum potential, you can find more on the latest research and best practice from Peak Performance, our monthly issue. Trial or subscribe right here.


  1. Br J Sports Med. 2011 Nov;45(14):1149-56
  2. Eur J Appl Physiol. 2013 Dec;113(12):3011-20
  3. Br J Sports Med. 2013 Sep 20. doi: 10.1136/bjsports-2013-092417. [Epub ahead of print]

Best practice
The most recent evidence suggests that in real-world conditions (i.e. outdoors with a degree of wind cooling – not in artificial laboratory conditions), more than 2% dehydration is NOT a problem for endurance athletes. This is contrary to a number of existing guidelines. Likewise, new research throws into doubt the recommendation that you “should not rely on your thirst and instead to follow a regular drinking plan”.

Shorter events (under 2 hours)

  • Rather than following a rigid programme of drinking, choosing when and how much to drink is likely to be as equally effective for performance – and less hassle too!
  • Contrary to popular opinion, using your sensation of thirst IS a useful way of ensuring you take in sufficient fluid.
  • Although the evidence suggests that athletes can be more flexible about drinking on the move, you should always aim to start your training/competition well hydrated.

Longer events

  • With more opportunity to become significantly dehydrated (over 3%) a more considered approach may be required in warm/hot conditions. Using training sessions as a guideline where you drink as you please, compare your body mass before and after 2-3 hours of training. If you’ve lost no more than 2% of body mass, your “freely chosen” drinking strategy is likely to be suitable for longer events. If you’re already 3% or more dehydrated, you might want to consider a more structured fluid intake.
  • For very long events where simply staying positive and finishing is the goal, drinking plenty to minimise thirst may help lift your mood by reducing perceived exertion and thermal stress!
  • Always start your training/competition well hydrated.


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Race pacing for runners: Rick Lovett looks at the science and art of race pacing for runners. In this article he:

  • Explores successful pacing strategies used by elite runners
  • Explains the role of the brain and psychology in race pacing
  • Examines useful mental techniques for use in race situations

Coming up short, hamstring tightness: In this article, Alicia Filley explains hot to measure your hamstrings and how their flexibility impacts your running.

No fear! Returning to sport after injury: Adam Nicholls provides you with a nuber of psychological strategies to make your return to sport much less daunting.

Yes or no to ketto? In our Dietary optimisation chapter, I take a close look at the scientific evidence behind the keto diet along with practical recommendations for athletes wishing to maximise performance.

Peak Performance Hotline: I look at some of the latest findings from the world of sport performance science where I discuss strength and endurance, riboflavin recovery and time-trial feedback.

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About Andrew Hamilton
I am the editor of Peak Performance and commissioning editor of and contributor for Peak Performance.

I am a sports science writer and researcher, specialising in sports nutrition and I’ve worked in the field of fitness and sports performance for over 30 years, helping athletes to reach their true potential. I am also a lifelong endurance athlete myself.


Andrew Hamilton
Andrew Hamilton
I’m dedicated to helping you improve your performance by unravelling the latest sports science and translating it into plain English and by giving you practical training recommendations that you can start using straight away.

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