I was thinking about this yesterday. After riding around 50 miles and seeing my performance drop off around mile 35 I was contemplating a few things, mainly why? Paris Roubaix was yesterday as well, dozens of water bottles were used, but what was in them?
Is it really possible in this day and age to race, or train hard on water alone?
I do think it is possible to train on water alone. In that, there is a drop in performance, and that if planned for, you can adapt and overcome those aspects. It is training after all, not where you have to see the performance of a lifetime. You are to gain fitness. So another question is will you gain more fitness on water, or some type of replacement drink?
Can you actually use a replacement drink too much to where it become ineffective? I do believe so. Your stomach can only handle so much, and is not 100% efficient. When using a replacement drink during exercise, we expect the stomach to transfer into our system those liquid contents, some of which do hit the intestines with hopes we derive benefits at some point. The reality is that the stomach cant pass all of that liquid, sugars and other goodies through at a massive rate. It really shouldn't after all, because if it passed all sugar through, we would have massive sugar blues afterwards.
So why would we have troubles on water alone? Well part of this is that we have to access stored reserves. Some of these reserves are in the muscle, and others held in other areas of the body. Again we are not terribly efficient in accessing those stores, so at some point we pay the price.
To combat this, we train for endurance, as well as recovery time so we can complete a high workload using less energy. It may not be as comfortable to do so, but using water only at this point should help to emphasize the natural systems in place, and build increased efficiency.
So perhaps the best thing we can do is to train on water alone, to emphasize the body's systems of building endurance, removing lactic acid and accessing energy stores. On event day, supplementing with a replacement is a great idea since we can capitalize on our training, and provide a supply of energy to prevent full use of muscle stores. In between, light use of replacement drinks to where you do not become saturated, but can tolerate and perform well is to be highlighted.