Recent research has pushed back on widely perpetuated hydration myths that would lead you to believe that guzzling two liters a day is absolutely required, finding instead that simply replacing the water that is displaced in urine and sweat will keep the body functioning properly.
“With an hour of moderately intense activity, with a temperature in the mid-80s, and moderate humidity, it’s not uncommon to lose a little over 2 pounds of water,” lead investigator Mindy Millard-Stanford said in a statement from July.
“If you do 12-hour fluid restriction, nothing by mouth, for medical tests, you’ll go down about 1.5 percent,” she said. “Twenty-four hours fluid restriction takes most people about 3 percent down. If you drop 4 or 5 percent, you’re going to feel really crummy."
Hoping to add upon the current literature, Millard-Stanford’s team at the Georgia Institute of Technology initiated a new study exploring whether exercise and heat stress alone can impact cognition, and how dehydration would exacerbate the matter.
The series of experiments, documented in Physiological Reports, involved 13 volunteers asked to perform a simple attention and motor function test over a 20-minute period while inside an fMRI scanner. Before the test, they engaged in one of three activity sessions: in the control, subjects lounged in a temperate room for about 90 minutes, and for the other two, they completed a 150-minute-long session of walk-rest cycles on a treadmill in a hot, 45°C (113°F) room, either with access to enough water to replace lost fluid or with no water (achieving ~3 percent loss).
All three sessions were conducted on separate days, and the fMRI tests were administered in air-conditioned rooms after a 45-minute cool-down.