Getting in a good workout really gets the blood flowing. It also results in lost fluids which can lead to dehydration. That's a big deal because losing as little as 2% of your body weight through fluids can negatively impact your performance. A study published in the International Journal of Sport Nutrition and Exercise Metabolism reports that cool or cold performance beverages promote hydration much more effectively than warm ones.
Analyzing 14 different studies investigating the relationship between beverage temperature and drinking habits, researchers found that during exercise active adults tend to consume half the volume of liquids when the beverage is warm (70 degrees or higher) compared to how much they drink when the beverage is cold (50 degrees) or cool (below 70 degrees).
Because subjects given warm beverages drank 50% less during exercise they lost 1.3% of their body weight. Those given cool or cold beverages better maintained their hydration status. Grabbing a performance beverage straight from your gym's cooler is probably even more important during the hot summer months.