Since I now live in the desert, the higher altitude fringe of the Las Vegas Valley, I’ve gained a lot of experience in running in these hot and dry conditions. To do well running in these conditions, i obviously had to learn how to hydrate effectively.
Workout hydration is a delicate balance. You need to hydrate to avoid the performance (and possibly health) damaging effects of dehydration. But if you consume more fluid than you need, you’re simply going to end up needing the restroom/toilet too often too soon to be worth the trouble.
Over my years of running I have through trial and error developed a useful approach to hydration that running in the hot Vegas desert has helped me fine tune into a reliable methodology.
It is worth noting that training with some degree of very mild dehydration can be useful for developing aerobic fitness. The line between useful and detrimental is very fine, not to mention the line between proper hydration and needlessly overloading your kidneys and bladder. You also must bear in mind that carrying hydration adds weight to your body and will to some subtle degree slow you down on your run.
Thus I don’t mind being a little “dry” during a training run, whether it’s an easy run, a harder speed workout, or a long run. However, I want to avoid tipping over the edge into performance loss from dehydration.
So, my objective is to go into a training session with a rudimentary amount of pre-run hydration, then hydrate as needed during or after the workout.