There are days when I’m so rushed to get to the office that I completely forget to drink a glass or two of water after my morning workout (especially if it’s cold out). Hours will go by before I realize—often in the middle of furiously typing yet another email—that my mouth is painfully dry. And, if you’re guilty of the same negligence, it turns out that our forgetfulness could actually be diminishing some of the heart-healthy benefits regular exercise provides.
Several studies have shown that after an intense workout, your body’s ability to regulate your heart rate is suppressed, which can increase the risk of lethal arrhythmias and cardiovascular mortality after vigorous exercise, even if you’re healthy. However, researchers from Brazil’s Federal University of Juiz de Fora recently discovered that drinking a few glasses of water after a high-intensity workout can slow your heart back down to its normal tempo in less time, which means it won’t be forced to work as hard to pump blood through your system, reducing the risk of complications.
So how do a few glasses of H2O make such a difference? During an intense workout session, you’ll sweat out anywhere from 1 to 4% of your body weight every hour, says William Adams, director of sports safety policy initiatives at the Korey Stringer Institute. That fluid’s coming from inside your cells and from the plasma in your blood. So as you sweat more and more, your plasma volume continues to decrease, Adams explains, and so there’s actually less blood for your heart to distribute around your body. And to maintain the blood flow your body needs, your heart rate speeds up by about 3 to 6 beats per minute.
To figure out the exact amount of water you’ll need to rehydrate, Adams suggests weighing yourself immediately before and after a workout, without drinking anything in between. You’ll want to drink about 150% of the water weight you just lost (that extra 50% is to make up for all the stuff you’ll inevitably pee out, he says). So if you weigh 1 pound less after an hour-long workout, you’ll need to drink 1.5 pounds of water or about 3 cups. You don’t need to force yourself to down it all immediately, says Adams, but the sooner you drink it, the sooner you’ll slow your heart rate back down to normal.