Whatever the true explanation may be, it is now certain that thirst-based drinking is the best drinking strategy for runners regardless of how much or how little fluid intake results from the use of this strategy and regardless of its effect on dehydration levels. The best proof comes from recent field studies involving elite runners in real races. In a 2012 study, for example, researchers estimated that the male winners of thirteen recent major marathons—all of whom appeared to drink by thirst—consumed only 18.4 ounces of fluid per hour on average and lost 8.8 percent of their body weight, reaching nearly five times the amount of dehydration that is often said to be detrimental to performance. Indeed, the winner of any given race is usually the most dehydrated finisher, because faster runners sweat more and are not able to drink as much. Drinking by thirst, drinking relatively little, and becoming significantly dehydrated clearly do not stop the best runners from winning races.
Whether or not you are in contention to win any races, drinking by thirst is the strategy you should use during races and training runs as well. This approach even works on the hottest days when the sweat rate is highest because runners naturally become thirstier and drink more in warmer environments, so there’s no need to consciously adjust your drinking rate based on the weather. Simply listening to your body is always sufficient. Here are the two basic guidelines:
1.There is no need to drink in runs lasting less than one hour. You can if you like as there’s no “crutch” effect associated with heavy reliance on fluid intake in the training process as there is with carbohydrate. But because drinking during runs lasting less than an hour does not aid performance and carrying fluid is a slight inconvenience, it is sensible to default to not drinking in these workouts.
2.Always have plenty of fluid available and drink according to your thirst in higher-intensity runs lasting longer than one hour and in all runs lasting longer than two hours. You will perform better and therefore get a greater training effect. In low- and moderate-intensity runs of between one and two hours’ duration, drinking probably won’t aid your performance but you may be more comfortable if you do drink by thirst in these instances. I typically do not drink in easy runs of less than ninety minutes.