Always hydrate before a workout, but then drink throughout, too, to keep your energy up and your body balanced, explains Rebecca Gahan, CPT, owner and founder of Kick@55 Fitness in Chicago. "You want to stay ahead of hydration versus chasing it," she says, as that's where it can leave you susceptible to heat exhaustion, early fatigue, and even heat stroke in extreme cases.
"While the exact amount [to drink] for you will depend on several factors, the daily recommendation is eight 8-ounce cups of water per day. You'll need more if you're working out regularly though, especially in the heat. So, during your workout, try to consume at least eight ounces every 15-30 minutes," adds Lindsey Mathews, CSCS, head trainer at IdealFit.