Up until 1965 athletes rarely drank during exercise. Even elite runners would complete entire marathons without swallowing a drop. This changed quickly, however, when the University of Florida did their study and created Gatorade and the first sports drinks hit the market. Along with these products came a flood of scientific research demonstrating that drinking during exercise not only limited dehydration itself but helped body temperature regulation and even enhanced performance. However much of the study was flawed and since then many studies have been performed the create very little validation to either side of the argument.
One of the original seminal studies led by sports drink inventor Robert Cade found that subjects undertaking a seven-mile walk in a hot environment stayed cooler and finished 3 percent faster when they drank a sports drink than when they drank nothing.
Studies like this one led to the notion that people should aim to completely prevent dehydration during exercise, which requires drinking the same amount of fluid that is lost through sweating.
Studies recently have called this idea into question. What scientists discovered was that, in many circumstances, it’s really hard — if not impossible — to drink enough to completely prevent dehydration during exercise. Forcing it results in symptoms of gastrointestinal distress such as sloshing, bloating, and nausea. During exercise the body tries to reserve its blood supply for the muscle groups. When excess fluids are consumed, blood must flood the stomach to help digest or absorb the fluids.
In recent studies, when individuals are allowed to choose their own drinking rate during exercise, they typically replace only 30 to 70 percent of the fluid they lose through sweating. As a result, they become dehydrated — not as dehydrated as they would if they didn’t drink at all, but more than they would if they tried to drink enough to match their sweat losses.
However, recent studies have shown that people perform better when they drink according to their thirst than they do when they are required to drink more, despite being more dehydrated when they finish.
In a 2012 study conducted by English researchers, experienced runners completed a 10-mile time trial 58 seconds faster, on average, when they drank by thirst than when they drank more. And when they drank more, their ratings of gastrointestinal discomfort were much higher. When athletes were 20% dehydrated they found their performance was above when they were 90% or 100% hydrated.
These findings jive with data from field studies involving athletes in real races. In 2015, French scientists reported that participants in a half-ironman triathlon lost more than 8 pounds between the start and finish due to failure to fully replace fluid lost through sweating. But there was no relationship between how dehydrated athletes became individually and their performance.
Does this mean that dehydration doesn’t matter? Not exactly. It just means that becoming a little dehydrated during exercise is not as costly as drinking more than you can tolerate in an effort to completely prevent dehydration.
We need to change the perception hydration to the focus of thirst and not loss. With objective measures that will enable exercisers to pinpoint their own personal optimums for hydration level and drinking rate in different circumstances.
It is important to recognize what most exercisers overlook: that your hydration status at the start of exercise matters more than your hydration status at the end of exercise.
Research has consistently shown that regardless of how little or how much people drink during exercise, they stay cooler and perform better if they are fully hydrated at the start. In a 2013 study, for example, Greek researchers found that cyclists took 5.8 percent longer to complete a 5 km hill climb when they started it in a state of mild dehydration compared to when they started it fully hydrated.
Here’s the bottom line: When it comes to hydrating your workouts, where you start is more important than how you finish. Drink throughout exercise. This will help you stay cooler and feel and perform better. But give equal attention to your hydration during the rest of the day so that you begin your workouts full hydrated and ready to give your best effort.