However, most of the time and for most individuals it does not matter. What is more, overhydration and hyponatremia are much more prevalent and a whole lot more problematic. Whereas dehydration in normal individuals under normal race conditions may lead to some loss of performance and maybe (maybe!) some cramping, hyponatremia can cause permanent brain damage and death. Even individuals who do not develop neurological symptoms will suffer more performance loss from gastro-intestinal ills due to overhydration (full stomach, fluid sloshing around, bloating) than they ever would from dehydration.
|Sodium chloride, aka table salt or NaCl|
Most of the ills attributed to dehydration have other causes. Cramping is a prime example. It is extremely common in marathon runners (40% according to one study) and its true cause is unknown. One thing is for sure: it has never been show to be caused by dehydration. Those who were dehydrated were no more likely to suffer cramps than those who were well hydrated. If anything cramping correlates better with training. Undertrained individuals are much more likely to suffer cramps than well trained athletes.
Eighteen percent (58) of the 330 finishers of the 1997 Ironman New Zealand were hyponatremic. A 2002 study in the Boston marathon found that 13% of non-elite competitors suffered from hyponatremia. That same year a Boston runner died of hyponatremia. Hyponatremia is so prevalent that the B.A.A. and W.T.C. started sending out flyers warning people of the dangers of hyponatremia.
Several symptoms of hyponatremia (i.e. overhydration) are similar to those of dehydration.
The best thing you can do to prevent dehydration in sunny locations is to cover your skin with clothing.
There is a strong belief out there that people need to drink before they feel thirsty. Many believe that poor performance can be fixed instantaneously by appropriate hydration. I have been with a lot of coaches in road races who yell at dropped athletes to drink more as if that would miraculously solve their problem.
Most people also believe that one needs to replace all the fluid (and calorie) losses sustained in a race, during that race. This notion is mistaken and makes no sense. One reason we developed a digestive system is so that we can interrupt our food and drink intake to take care of other matters -like running away from predators or searching for more food and water.
The longer the race the more modest your fluid needs (per unit time) will be as your body will adjust to initial losses and prevent further losses to the extent possible. The better trained you are the better it will work. Here are some things I learned about food and drink during a long race.