According to the National Athletic Trainers' Association (NATA), Research shows that relying on thirst may cause athletes to underestimate fluid needs and replace on average only about 50% of the fluid lost in sweat. Therefore, the NATA recommends athletes drink on a schedule based on their individual sweat rate, regardless of thirst, to ensure that they are replacing sweat losses.
NATA recently convened an Inter-Association Task Force comprised of 18 sports medicine groups and injury prevention and health professional organizations to release an Exertional Heat Illnesses Consensus Statement. The Consensus Statement, which applies to activity at all levels of intensity, states:
THIRST IS NOT ENOUGH: There is scientific research to support the idea that thirst is not an optimal way to determine when and how much an athlete should drink. By the time an athlete is thirsty, they are already somewhat dehydrated and in most cases will not drink enough to fully replace the fluids lost in sweat.
TO BE SAFE, KNOW YOUR SWEAT RATE: Rather than relying on thirst or simply drinking as much as you can tolerate (which can also be dangerous), knowing how much you sweat is the best way to determine hydration needs. To figure out how much you sweat, weigh yourself before and after exercise. The weight you lost in ounces represents fluid and that amount is how much should be consumed (in total) before, during and after exercise to adequately replace sweat and keep the body balanced.
REPLACE FLUIDS & ELECTROLYTES LOST: Optimal hydration is the replacement of fluids and electrolytes based on individual needs. Drinking a sports drink helps replace the key electrolytes lost in sweat.
For more information, please visit the National Athletic Trainers' Association website.