Enlytens are electrolyte strips. They come in little cartridges that you carry while running. You pull them out and tuck them up between your gum and cheek. If you cramp up during long runs these may be the solution. At least I found that they work quite well. I used to get terrible calf cramps during marathons. No more! It takes some practice to get the hang of pulling them out so make sure you try them out a few times during training. Since each has a pretty small dose you can keep taking them as you feel necessary without any real risk. I generally start races with two (one in each cheek) and then use two or three at a time every few miles. I introduced two of my racing friends to them and now both use them regularly.