National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active

NATA's 2017 statement on hydration updates its 2000 statement on fluid replacement for athletes. Its starting point is that both drinking too little (hypohydration) and drinking too much (hyperhydration) can hurt performance and become dangerous, so the aim is enough fluid but not too much.

Because sweat rates, thirst and drinking habits vary widely from person to person, it recommends individualized hydration plans built from each person's measured sweat rate, the environment, heat acclimatization, body size and the length and intensity of exercise. It asks athletic trainers to aim for athletes to start exercise close to their normal hydration and to lose less than 2% of body mass by the end, and warns that no one should gain weight during exercise: drinking more than is lost, especially of low-sodium fluids, is what causes exercise-associated hyponatremia.

For day-to-day practice it recommends educating athletes, parents and coaches; keeping palatable fluids easy to reach; refueling with fluid, electrolytes, carbohydrate and protein within 2 hours after activity; tracking hydration with body-mass changes against a baseline and first-morning urine; and individualizing sodium intake. It finds that moderate caffeine does not cause fluid loss during exercise and does not recommend glycerol hyperhydration.