Most gridiron warriors are significantly dehydrated even before stepping between the sidelines, according to a new study out of Indiana State University.

The researchers found that as many as four out of five members of one college squad showed signs of dehydration during preseason physical exams. With such grueling workouts, sometimes twice a day, it’s no wonder that approximately 80 percent of NCAA Division I football players and 50 percent of NFL’ers were found to be dehydrated.

The aftermath: “It's going to affect an athlete’s physical performance—they’re not going to have the dexterity to catch the ball correctly, they’re also going to have cognitive effects such as trouble remembering plays,” the study’s author explains. “And physiologically, their core body temperature could be higher than it should have been if they were hydrated. Their heart rate will be higher, and they’re going to perceive that they’re working harder than they actually are.”

Interestingly, when the scientists studied athletes from other sports, the dehydration rate was much lower.

To make sure you’re well hydrated, drink enough water so that your urine color is clear—dark yellow or brown indicates trouble.