The history of drinking during endurance exercise is an interesting one. It serves as a wonderful lesson for two reasons. First, it demonstrates a concept I’ve discussed at length before called the Hype cycle where a particular concept or method goes through a cycle of first overemphasis, then under emphasis, before eventually settling into its rightful place. This cycle can be seen almost anywhere, but in terms of training you’ve seen it with such things as “core” training, mileage, and interval training.
Secondly, the history of hydration demonstrates that we tend to overemphasize what we can measure and to ascribe more meaning initially than we deserve. As you’ll soon see, there was nothing wrong with the scientific measurements taken throughout the study of hydration, the problem has been the interpretation of those measurements.