If you have been running for a while, you have almost certainly heard that it is essential to remain well hydrated. Dehydration has been blamed for premature fatigue, pulled muscles, cramps, dizziness, nausea and heat exhaustion. But what are the facts?

I have recently been reading The Runner's Body by Tucker and Dugas , and it is interesting to read their view on this subject. They note that runners who finish marathons in the fastest times are those who lose the most weight – typically about eight pounds. The proponents of avoiding dehydration recommend that you should attempt to replace the water you use during a run.

Do you really believe that elite runners would finish faster if they drank a gallon of water during a marathon? If so, I wonder why nobody has tried it yet!

The truth is that all this talk about dehydration is greatly exaggerated. Marathoners, and even ultra-marathoners, showed little concern about hydration until recently. Even now, there are more issues with hyponatremia (due to too much water in the bloodstream) while running than with dehydration.

Hyponatremia is the main reason behind the promotion of sports drinks for runners. It all started with Gatorade back in the 1960s, when researchers found that most professional football teams played better in the first half than the second half of the game. So sports drinks, starting with Gatorade, were developed to solve the problem of second-half fatigue.

There is a huge difference between professional footballers (moving in short, fast bursts with long breaks and carrying several pounds of extra equipment) and long distance runners!

I shall discuss this subject in depth in my next newsletter, due Friday January 1, 2010. In this letter I'll give you my recommendations on what to drink (water or sports drinks) and how much, for both training runs and races.

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Runner's World The Runner's Body: How the Latest Exercise Science Can Help You Run Stronger, Longer, and Faster (Runners World)