When athletes become dehydrated they need both glucose and salts as well as water. Why the salts?
As previously mentioned, when an athlete sweats they loose both salt and water. This can leave blood and plasma of the preferred salt concentration but not enough of it. The other components of the blood are too concentrated to work well. If the athlete then drinks water without salts the water is absorbed into the blood and the blood then is not concentrated enough. The movement of substances to muscles is affected as is the pH and osmotic balance of the blood. The kidneys will respond by removing the “excess” water recreating the dehydration. This cycle forces the athlete to urinate. Eventually the athlete will collapse. The process is worse if the athlete has not eaten that morning since food contains salts. There are coaches who actually recommend pure water, I don’t think much of them.
