I'm not super athletic, so I can't speak for this thing in marathons. But I did take them hiking w/ me. They work like a charm. I can be dead tired and not able to take another step, pop one or two, chew, add water, and off I go again. My personal favorite is the blueberry pomegranate. Also I've found that if I open a pack and come back to it tomorrow (or even a few days after), it's still good, just the outside dries slightly, making it less chewy.