You know how it feels to exercise in 90-degree heat if you skimped on water beforehand. Now, new research has quantified dehydration’s actual physical effect on performance and led to a new way to think about watering up pre-workout.
According to the Journal of Strength and Conditioning Research, for every 1% body mass you lose through sweat, your heart rate ticks up three beats a minute, which means it has to work harder. Not good. On the flip side, “staying hydrated helps hold in more water, so your heart has to work less to pump the blood to muscles,” says study author William Adams, M.S., A.T.C., so “keeping your heart rate low allows you to exercise with a higher intensity.”
The key is to hydrate before your workout, not just during, Adams says. As for how much to drink, use your next workout to figure it out: Weigh yourself before and after exercise, and note how much “sweat weight” you lost then, before your next workout, be sure to take in that weight in liquid.