When we go for a run our body temperature increases and this is when we normally start to sweat. One of the reasons we sweat is so our bodies can cool down.
 

When we sweat we need to think about replacing the fluid that we lose during this process.  One of the big questions that has been explored over the years is how much fluid should we be replacing when we are exercising and should we be having any special types of drinks to replace what we are losing from sweating. This is an interesting topic which has been influenced a lot by marketers trying to sell you products that tell you will perform better if you buy their product. 
 

The current scientific research may surprise you. The way to measure how much you drink when you exercise is your thirst and that we don't actually need electrolytes. Electrolytes have no effect on performance, they are basically a waste of your money, so how do you use this knowledge? The key thing is to make sure you don't go into a session feeling thirsty, make sure you have had a drink within 30mins of the start of your session and choose a drink that has carbohydrates which will provide you with some energy but there's no need to go hard out with electrolytes.
 

Drinking is important for athletes but it's not as complicated as we once thought. Stick to the rule that thirst is your gauge and you will be fine.