Stay Hydrated

I drink water almost exclusively—save my current addiction to homemade smoothies and the occasional margarita—but you have to know how to best use this source of hydration to benefit your body if you hope to reap it's numerous benefits:

Before a long run, a race, or a training workout, drink plenty of fluids. The day before an event, drink extra water, 100 percent juice and/or other nutrient-rich fluids such as nonfat or 1 percent milk. Monitor the color of your urine. The goal is pale yellow, not clear... 

...Every athlete has unique hydration needs. By weighing yourself before and after exercise, you can estimate the volume of fluid your body requires to remain hydrated during exercise... 

...To help you determine the amount of fluid you lose during exercise, you can weigh yourself before and after exercise. For each pound lost during activity, drink 24 oz. of fluid. If your body weight increased, you have overhydrated and you should drink less fluid in future exercise sessions. (Katie Jeffrey-Lunn, "How to Hydrate Before, During, and After a Workout", Active.com)

The most important aspect of this article...STAY HYDRATED. It's very important, particularly if you're training in high temperatures, to keep the water bottle handy. If you're feeling sluggish or light-headed, chances are you've not had enough food or water. Training minus the appropriate amount of either is counter-productive to reaching/maintaining your fitness goals.