Dehydration is defined as the loss of body water and important ions (blood salts like potassium and magnesium).
Over the years advice on hydration has changed to what it is now of "Drink to Thirst". It can be a tricky balance especially in very hot weather where fluid intake and sweat rates are high. In this situation if electrolytes aren't replaced, they can become diluted / depleted if all you are drinking is plain water.
This from an article found in Nutrition News section from "The Sport Factory" written by Llana Katz MS, RD, LD titled "To Salt or Not To Salt"
Athletes will lose copious amounts of sodium through sweat in high intensity and/or heated conditions. Athletes training for long endurance events in hot and humid environments may require extra sodium as a part of their hydration strategies. Sodium is the “gate keeper” of fluid in your body. It enables the body to hold onto water for hydration, plays a role in hydration on the cellular level, and the normal function of glucose entry into cells to be used as energy.
For those training for a spring marathon during the cooler autumn and winter months, electrolyte balance is less of an issue although you still need to bear it mind. If training through the hot summer months, it is something that you must factor in. If your electrolyte balance slips it's likely there will be several outcomes. One will be nausea which will then have a knock on effect to your fuelling strategy because you wont feel like fuelling. You can then get stuck in a bit of a vicious cycle. Another will be cramping.
While running you lose electrolytes through your sweat, mainly sodium and potassium. Potassium permits the movement of fluids and nutrients across your cells’ membranes, thus allowing them to carry on their metabolic activities such as contacting muscles. Without sufficient potassium, your muscles cells can’t generate the necessary nerve impulses that control muscle contraction. Cramping is the body’s way of letting you know the electrolyte tank is empty and it cannot continue; it’s like a car running out of gas. Even you’ve never experienced cramping, electrolytes need to be replenished after sessions longer than a hour to facilitate optimal recovery. More on electrolytes in general in this great article from Abby Housefield, resident nutritionist at Runners Connect.
Read the full article - Click Here
There are various options for taking electrolytes. One is by using products such as nuun or zero (others are available) which are dissolved in water and then drunk. One thing to bear in mind with these products is that they contain artificial sweetener, flavouring and what ever else they contain that makes them fizz. Prolonged use may cause issues of their own.
While not wanting to promote any product, a good option is to use an electrolyte tablet such a Succeed S!caps. These are simply taken one per hour (or more or less depending on temperature / sweat rate) with water. These tablets contain 100% pure electrolytes in the correct balance with no fillers / sugars etc. Other brands are available. Another recommended product is "SOS Rehydrate" which is now the official rehydration partner of England Athletics.
Of course eating proper food as fuel while on a long run may provide you with some natural electrolytes.
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