听力原文：As a personal fitness trainer, I have to tell you that one of the worst things you can do when you're working out at the gym is drink soda. Aside from making you feel bloated, the sugars in the soda keep your body from absorbing water, which can make your muscles cramp up. I mean, I don't even recommend those so-called juice 'drinks' that contain a bunch of added sweeteners. Stick to the natural stuff: one hundred percent juice is great—it contains fructose, which helps you rebuild your muscles, and vitamins and... like that. If you want, you can make your own sports drink by diluting some juice and adding a little salt— I add about a teaspoon for every quart of diluted juice. This helps keep you hydrated, and helps you replenish the salts you sweat out. What does the speaker say to avoid before exercise?