Take a look at the most popular endurance sport drinks, and you'll notice a surprising similarity in ingredients.
There are carbohydrates (usually in the form of sugar), sodium, potassium and sometimes a touch of protein.
You'll notice something else -- these drinks are expensive.
It can cost $1.75 or more to fill one 24-ounce water bottle -- and you have to drink a bottle an hour to keep up a good flow of nutrients and liquid while you work out.
There's an easy way around the expense: making your own endurance drink. It may not have all the bells and whistles of the top brands, but it should be more than enough for a long ride or run into the mountains. After all, water is the most crucial ingredient, and it's free.