Research points to a link between dehydration and mental performance.
People who like to work up a sweat should definitely have proper hydration practices on their mind. A review in Medicine & Science in Sports & Exercise found strong evidence that athletes who lose more than 2% of their body weight in fluids—all too common in prolonged bouts of sweaty exercise—suffer noticeable declines in mental performance. The review (a meta-analysis of previously published research) noted declines in attention, motor coordination, and the executive functioning your brain needs to focus, organize and remember details.
Dehydration can be particularly detrimental to people in sports like tennis and mountain biking, as these activities need a certain level of brain power and coordination. But also think about group fitness participants who sweat buckets in an indoor cycling class and don’t drink enough before or afterward. Following class, they may have to tackle tasks like driving and work projects that require mental ability. This is a good reminder of why education about sound hydration practices should be part of any exercise program.